publicationDate,title,abstract,id 2007-05-25,Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys,"Half-metallic Heusler alloys are among the most promising materials for future applications in spintronic devices. Although most Heusler alloys are ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated ferrimagnetic) alloys would be more desirable for applications due to the lower external fields. Ferrimagnetism can be either found in perfect Heusler compounds or achieved through the creation of defects in ferromagnetic Heusler alloys.",0705.3731v1 2005-10-11,Introduction to half-metallic Heusler alloys: Electronic Structure and Magnetic Properties,"Intermetallic Heusler alloys are amongst the most attractive half-metallic systems due to the high Curie temperatures and the structural similarity to the binary semiconductors. In this review we present an overview of the basic electronic and magnetic properties of both Heusler families: the so-called half-Heusler alloys like NiMnSb and the the full-Heusler alloys like Co$_2$MnGe. \textit{Ab-initio} results suggest that both the electronic and magnetic properties in these compounds are intrinsically related to the appearance of the minority-spin gap. The total spin magnetic moment $M_t$ scales linearly with the number of the valence electrons $Z_t$, such that $M_t=Z_t-24$ for the full-Heusler and $M_t=Z_t-18$ for the half-Heusler alloys, thus opening the way to engineer new half-metallic alloys with the desired magnetic properties.",0510276v1 2022-08-07,A machine learning approach to predict the structural and magnetic properties of Heusler alloy families,"Random forest (RF) regression model is used to predict the lattice constant, magnetic moment and formation energies of full Heusler alloys, half Heusler alloys, inverse Heusler alloys and quaternary Heusler alloys based on existing as well as indigenously prepared databases. Prior analysis was carried out to check the distribution of the data points of the response variables and found that in most of the cases, the data is not normally distributed. The outcome of the RF model performance is sufficiently accurate to predict the response variables on the test data and also shows its robustness against overfitting, outliers, multicollinearity and distribution of data points. The parity plots between the machine learning predicted values against the computed values using density functional theory (DFT) shows linear behavior with adjusted R2 values lying in the range of 0.80 to 0.94 for all the predicted properties for different types of Heusler alloys. Feature importance analysis shows that the valence electron numbers plays an important feature role in the prediction for most of the predicted outcomes. Case studies with one full Heusler alloy and one quaternary Heusler alloy were also mentioned comparing the machine learning predicted results with our earlier theoretical calculated values and experimentally measured results, suggesting high accuracy of the model predicted results.",2208.12705v1 2007-11-15,Characterization of half-metallic L2_1-phase Co_2FeSi full-Heusler alloy films formed by rapid thermal annealing,"The authors developed a preparation technique of Co_2FeSi full-Heusler alloy films with the L2_1-ordered structure on silicon-on-insulator (SOI) substrates, employing rapid thermal annealing (RTA). The Co_2FeSi full-Heusler alloy films were successfully formed by RTA-induced silicidation reaction between an ultrathin SOI (001) layer and Fe/Co layers deposited on it. The highly (110)-oriented L2_1-phase polycrystalline full-Heusler alloy films were obtained at the RTA temperature of 700 C. Crystallographic and magnetic properties of the RTA-formed full-Heusler alloy films were qualitatively the same as those of bulk full-Heusler alloy. This technique is compatible with metal source/drain formation process in advanced CMOS technology and would be applicable to the fabrication of the half-metallic source/drain of MOSFET type of spin transistors.",0711.2404v1 2023-02-13,"Structural, magnetic and elastic properties on stoichometric $Ni-Mn-Cu$ Heusler alloys","Heusler alloys with $Ni-Mn-Cu$ (all d-transition metal) composition have been studied; equilibrium structures for different magnetic configurations are found. Elastic constants and tetragonal distortion are analyzed. Distortion effect on densities of electronic state peaks are characterized. For this ternary family of alloys, we find that the one with the most interesting properties and mechanical stability is $Ni_2MnCu$.",2302.06472v2 2015-01-16,A first-principle study on some quanternary Heusler alloys with 4d and 3d transition metal elements,"In this letter, we investigate the magnetic properties, electronic structures, Slater-Pauling behaviours of some quanternary Heusler alloys with 4d and 3d transition metal elements. The energy levels of the minority-spin electronic band structures for all our calculated alloys are discussed. We have summaried 21 quanternary Heusler alloys. Our calculations indicate that the half metals ZrCoCrSi, ZrCoCrIn, ZrCoFeSi, ZrFeVAl, ZrFeVGa and NbFeCrAl have large spin-flip gaps.",1501.03871v1 2023-06-29,High-throughput design of all-d-metal Heusler alloys for magnetocaloric applications,"Due to their versatile composition and customizable properties, A$_2$BC Heusler alloys have found applications in magnetic refrigeration, magnetic shape memory effects, permanent magnets, and spintronic devices. The discovery of all-$d$-metal Heusler alloys with improved mechanical properties compared to those containing main group elements, presents an opportunity to engineer Heuslers alloys for energy-related applications. Using high-throughput density functional theory calculations, we screened magnetic all-$d$-metal Heusler compounds and identified 686 (meta)stable compounds. Our detailed analysis revealed that the inverse Heusler structure is preferred when the electronegativity difference between the A and B/C atoms is small, contrary to conventional Heusler alloys. Additionally, our calculations of Pugh ratios and Cauchy pressures demonstrated that ductile and metallic bonding are widespread in all-$d$-metal Heuslers, supporting their enhanced mechanical behaviour. We identified 49 compounds with a double-well energy surface based on Bain path calculations and magnetic ground states, indicating their potential as candidates for magnetocaloric and shape memory applications. Furthermore, by calculating the free energies, we propose that 11 compounds exhibit structural phase transitions, and propose isostructural substitution to enhance the magnetocaloric effect.",2306.17092v1 2008-01-15,Fundamentals of half-metallic Full-Heusler alloys,"Intermetallic Heusler alloys are amongst the most attractive half-metallic systems due to the high Curie temperatures and the structural similarity to the binary semiconductors. In this review we present an overview of the basic electronic and magnetic properties of the half-metallic full-Heusler alloys like Co$_2$MnGe. Ab-initio results suggest that the electronic and magnetic properties in these compounds are intrinsically related to the appearance of the minority-spin gap. The total spin magnetic moment in the unit cell, $M_t$, scales linearly with the number of the valence electrons, $Z_t$, such that $M_t=Z_t-24$ for the full-Heusler alloys opening the way to engineer new half-metallic alloys with the desired magnetic properties. Moreover we present analytical results on the disorder in Co$_2$Cr(Mn)Al(Si) alloys, which is susceptible to destroy the perfect half-metallicity of the bulk compounds and thus degrade the performance of devices. Finally we discuss the appearance of the half-metallic ferrimagnetism due to the creation of Cr(Mn) antisites in these compounds and the Co-doping in Mn$_2$VAl(Si) alloys which leads to the fully-compensated half-metallic ferrimagnetism.",0801.2252v1 2018-12-18,Atomistic study of an ideal metal/thermoelectric contact: the full-Heusler/half-Heusler interface,"Half-Heusler alloys such as the (Zr,Hf)NiSn intermetallic compounds are important thermoelectric materials for converting waste heat into electricity. Reduced electrical resistivity at the hot interface between the half-Heusler material and a metal contact is critical for device performance, however this has yet to be achieved in practice. Recent experimental work suggests that a coherent interface between half-Heusler and full-Heusler compounds can form due to diffusion of transition metal atoms into the vacant sublattice of the half-Heusler lattice. We study theoretically the structural and electronic properties of such an interface using a first-principles based approach that combines {\it ab initio} calculations with macroscopic modeling. We find that the prototypical interface HfNi$_2$Sn/HfNiSn provides very low contact resistivity and almost ohmic behavior over a wide range of temperatures and doping levels. Given the potential of these interfaces to remain stable over a wide range of temperatures, our study suggests that full-Heuslers might provide nearly ideal electrical contacts to half-Heuslers that can be harnessed for efficient thermoelectric generator devices.",1812.07189v1 2020-10-09,Structural and magnetic properties of epitaxial films of CoIrMnAl equiatomic quaternary Heusler alloy designed from first-principles calculation,"MgO-barrier magnetic tunnel junctions with half-metallic Heusler alloy electrodes attracted much attentions for spintronics applications. However, a couples of issues related to materials still remain to be resolved for practical uses. Recently, quarterly equiatomic Heusler alloys attracted attentions as advanced Heusler alloys. CoIrMnZ (Z = Al, Si, Ga, and Ge) half-metallic Heusler alloys were designed and predicted to have moderate Curie temperatures and to be a lattice-matched with the MgO barrier, being advantageous to traditional Co2 Heusler alloys [T. Roy et al., J. Magn. Magn. Mater. 498, 166092 (2020)]. Here we experimentally investigated structure and magnetic properties for thin films of one of those alloys, CoIrMnAl with a sputtering deposition. We successfully obtained the films with the B2 chemical ordering even with no post-annealing process. The lattice constant for the films annealed at 500-600$^\circ$C approximates the predicted values. The magnetization at 10 K was near 500 kA/m and the Curie temperature was approximately 400 K were observed, which were about 70% of the values predicted for the fully ordered structure. The magnetic properties observed in those B2 ordered films were well explained by ferrimagnetism appeared in B2 ordered CoIrMnAl with full-swap disorders of Co-Ir and Mn-Al and almost full-swap disorder of Co-Mn, predicted from the first-principles calculations.",2010.04369v1 2018-02-20,Ultrafast magnetization dynamics in pure and doped Heusler and inverse Heusler alloys,"By using a multiscale approach based on first-principles density functional theory combined with atomistic spin dynamics, we investigate the electronic structure and magnetization dynamics of an inverse Heusler and a Heusler compound and their alloys, i. e. Mn$_{2-x}Z_x$CoAl and Mn$_{2-x}Z_x$VAl, where $Z$ = Mo, W, Os and Ru, respectively. A signature of the ferrimagnetic ordering of Mn$_{2}$CoAl and Mn$_{2}$VAl Heusler alloys is reflected in the calculated Heisenberg exchange constants. They decay very rapidly with the interatomic distance and have short range, which is a consequence of the existence of the finite gap in the minority spin band. The calculated Gilbert damping parameter of both Mn$_2$CoAl and Mn$_2$VAl is high compared to other half-metals, but interestingly in the particular case of the inverse Mn$_{2}$CoAl alloys and due to the spin-gapless semiconducting property, the damping parameters decrease with the doping concentration in clear contradiction to the general trend. Atomistic spin dynamics simulations predict ultrafast magnetisation switching in Mn$_{2}$CoAl and Mn$_{2}$VAl under the influence of an external magnetic field, starting from a threshold field of $2\text{T}$. Our overall finding extends with Heusler and inverse Heusler alloys, the class of materials that exhibits laser induced magnetic switching.",1802.07195v1 2021-08-11,DFT and Monte Carlo simulations of the equiatomic quaternary Heusler Alloy CoFeCrP,"In this work, we study the equiatomic quaternary Heusler Alloy CoFeCrP using two methods: DFT and Monte Carlo simulations. The DFT method allowed us to illustrate the structural, electronic and magnetic properties of this alloy. The ground state phase diagrams have been presented to show the stable configurations in different physical parameter planes. On the other hand, the Monte Carlo simulations, performed under the Metropolis algorithm, permitted to deduce the critical the behavior of the equiatomic quaternary Heusler alloy CoFeCrP. The structural properties results show that the phase of type I, of this alloy is the most stable configuration. In addition, the band structures, and density of states calculations results show that this compound exhibits a half-metallic character with a 100 % of spin polarization (SP) at the Fermi-level. The total magnetic moment of the Heusler compound is found to be 4.00 mu_B. Moreover, it is found that the Slater-Pauling is well described for this alloy. Our results show that this material is a potential candidate for the spintronic applications. This is due to its half-metallicity, its high spin moments, its complete SP polarization and its high Curie temperature.",2108.05160v1 2002-09-24,On Order-Disorder ($L2_1 \to B2^\prime$) Phase Transition in Ni$_{2+x}Mn_{1-x}$Ga Heusler Alloys,"Order-disorder phase transition in Ni$_{2+x}Mn_{1-x}$Ga Heusler alloys has been studied. It was found that the $L2_1 \to B2^{\prime}$ phase transition in Ni2+xMn1-xGa (x = 0.16 - 0.20) Heusler alloys is of second order and the temperature of this transition decreases with Ni excess.",0209547v1 2004-08-03,Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys,"Introductory chapter for the book ""Halfmetallic Alloys - Fundamentals and Applications"" to be published in the series Springer Lecture Notes on Physics, P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical work on the half-metallic Heusler alloys.",0408068v1 2002-05-07,Slater-Pauling Behavior of the Half-Ferromagnetic Full-Heusler Alloys,"Using the full-potential screened Korringa-Kohn-Rostoker method we study the full-Heusler alloys based on Co, Fe, Rh and Ru. We show that many of these compounds show a half-metallic behavior, however in contrast to the half-Heusler alloys the energy gap in the minority band is extremely small. These full-Heusler compounds show a Slater-Pauling behavior and the total spin-magnetic moment per unit cell (M_t) scales with the total number of valence electrons (Z_t) following the rule: M_t=Z_t-24. We explain why the spin-down band contains exactly 12 electrons using arguments based on the group theory and show that this rule holds also for compounds with less than 24 valence electrons. Finally we discuss the deviations from this rule and the differences compared to the half-Heusler alloys.",0205129v2 2016-08-10,Equiatomic quaternary Heusler alloys: a material perspective for spintronic applications,"Half-metallic ferromagnetic (HMF) materials show high spin polarization and are therefore interesting to researchers due to their possible applications in spintronic devices. In these materials, while one spin sub band has a finite density of states at the Fermi level, the other sub band has a gap. Because of their high Curie temperature and tunable electronic structure, HMF Heusler alloys have a special importance among the HMF materials. Full Heusler alloys with the stoichiometric composition X2YZ (where X and Y are the transition metals and Z is a sp element) have the cubic structure with four interpenetrating fcc sublattices. When each of these four fcc sublattices is occupied by different atoms, a quaternary Heusler structure with different structural symmetry is obtained. Recently, these equiatomic quaternary Heusler alloys (EQHAs) with 1:1:1:1 stoichiometry have attracted a lot of attention due to their superior magnetic and transport properties.",1608.03088v1 2021-02-22,High T$_C$ ferromagnetic inverse Heusler alloys: A comparative study of Fe$_2$RhSi and Fe$_2$RhGe,"We report the results of experimental investigations on structural, magnetic, resistivity, caloric properties of Fe$_2$RhZ (Z=Si,Ge) along with \textit{ab-initio} band structure calculations using first principle simulations. Both these alloys are found to crystallize in inverse Heusler structure but with disorder in tetrahedral sites between Fe and Rh. Fe$_2$RhSi has saturation moment of 5.00 $\mu_B$ and while its counterpart has 5.19 $\mu_B$. Resistivity measurement reveals metallic nature in both of them. Theoretical simulations using generalized gradient approximation(GGA) predict inverse Heusler structure with ferromagnetic ordering as ground state for both the alloys. However it underestimates the experimentally observed moments. GGA+$U$ approach, with Hubbard $U$ values estimated from density functional perturbation theory helps to improve the comparison of the experimental results. Fe$_2$RhSi is found to be half metallic ferromagnet while Fe$_2$RhGe is not. Varying $U$ values on Fe and Rh sites does not change the net moment much in Fe$_2$RhSi, unlike in Fe$_2$RhGe. Relatively small exchange splitting of orbitals in Fe$_2$RhGe compared to that of Fe$_2$RhSi is the reason for not opening the band gap in the minority spin channel in the former. High ordering temperature and moment make Fe$_2$RhSi useful for spintronics applications.",2102.10967v1 2004-07-21,Orbital magnetism in the half-metallic Heusler alloys,"Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are almost completely quenched and they are negligible with respect to the spin moments. The change in the atomic-resolved orbital moments can be easily explained in terms of the spin-orbit strength and hybridization effects. Finally I discuss the orbital and spin moments derived from X-ray magnetic circular dichroism experiments.",0407560v1 2014-09-23,The shifts X-Ray Mn Kα and 2p spectra of Mn-Heusler alloys,"X-ray emission K{\alpha}1,2 spectra of Mn in Heusler alloys Co2MnMe (Me = Al, Ga, Sb), Ni2MnIn, Cu2MnAl were studied. Shifts of Mn K{\alpha}1,2 lines relatively pure Mn in high-energy region and low-energy shifts of binding energy Mn 2p XPS is detected. X-ray emission and XPS shifts are in qualitative agreement.",1409.6375v1 2014-10-08,Direct Measurement of Magnetocaloric Effect in Metamagnetic Ni43Mn37.9In12.1Co7 Heusler Alloy,"The magnetocaloric effect in the metamagnetic Ni43Mn37.9In12.1Co7 Heusler alloy is directly studied experimentally under the adiabatic and quasi-isothermal conditions in a magnetic field with induction of up to 14 T.",1410.2139v1 2019-10-29,Perpendicular magnetic anisotropy in Pt/Co-based full Heusler alloy/MgO thin films structures,"Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a key ingredient for the development of electrically controlled spintronic devices. Due to their relatively large spin-polarization, high Curie temperature and low Gilbert damping the Co-based full Heusler alloys are of special importance from a scientific and applications point of view. Here, we study the mechanisms responsible for the PMA in Pt/Co-based full Heusler alloy/MgO thin films structures. We show that the ultrathin Heusler films exhibit strong PMA even in the absence of magnetic annealing. By means of ferromagnetic resonance experiments, we demonstrate that the effective magnetization shows a two-regime behavior depending on the thickness of the Heusler layers. Using Auger spectroscopy measurements, we evidence interdiffusion at the underlayer/Heusler interface and the formation of an interfacial CoFe-rich layer which causes the two-regime behavior. In the case of the ultrathin films, the interfacial CoFe-rich layer promotes the strong PMA through the electronic hybridization of the metal alloy and oxygen orbitals across the ferromagnet/MgO interface. In addition, the interfacial CoFe-rich layer it is also generating an increase of the Gilbert damping for the ultrathin films beyond the spin-pumping effect. Our results illustrate that the strong PMA is not an intrinsic property of the Heusler/MgO interface but it is actively influenced by the interdiffusion, which can be tuned by a proper choice of the underlayer material, as we show for the case of the Pt, Ta and Cr underlayers.",1910.13107v1 2017-11-01,Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering,"We report a systematic investigation on the magnetization relaxation properties of iron-based half-metallic Heusler alloy Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved ferromagnetic resonance. Band structure engineering through Co doping (x) demonstrated by first-principles calculations is shown to tune the intrinsic magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the intrinsic damping constants for samples with high Co concentration are among the lowest reported for Heusler alloys and even comparable to magnetic insulator yttrium iron garnet. Furthermore, a significant reduction of both isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys was found in the FCCS films with x=0.5-0.75, which is of particular importance for applications. These results demonstrate a practical recipe to tailor functional magnetization for Heusler alloy-based spintronics at room temperature",1711.00406v1 2022-04-13,Influence of Co and Mn on Electronic and Magnetic properties of Ni2MnGa Heusler alloy,"The ferromagnetic Heusler alloy $Ni_2MnGa$ had been of major interest in the past few years because of its magnetic properties which can be easily tuned. The $Ni_2MnGa$ Heusler alloys are intermetallic alloy with $L2_1$ structure. Here we report a detailed investigation of the effect of doping of Co and Mn in Ni2MnGa. Magnetic properties and electronic structure of $Ni_{2-x}Co_xMnGa_{1-y}Mn_y$ Heusler alloys have been studied by using Green's function-based KKR-CPA method based DFT calculations. We will show the magnetization can be tuned depending on the Co and Mn occumencies. We will also discuss the critical temperature, magnetic interactions and magnetic stability of the systems.",2204.06140v4 2023-06-25,"First-principles study of disordered half-Heusler alloys \textit{X}Fe$_{0.5}$Ni$_{0.5}$Sn (\textit{X} = Nb, Ta) as thermoelectric prospects","High lattice thermal conductivity in half-Heusler alloys has been the major bottleneck in thermoelectric applications. Disordered half-Heusler alloys could be a plausible alternative to this predicament. In this paper, utilizing first-principles simulations, we have demonstrated the low lattice thermal conductivity in two such phases, NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn, in comparison to well-known half-Heusler alloy TiCoSb. We trace the low thermal conductivity to their short phonon lifetime, originating from the interaction among acoustic and low-lying optical phonons. We recommend nanostructuring as an effective route in further diminishing the lattice thermal conductivity. We further predict that these alloys can be best used in the temperature range 400-600~K and carrier concentration of less than 10$^{21}$ carriers cm$^{-3}$. We found $\sim$35\% and $\sim$17\% enhancement in $ZT$ for NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn, respectively, as compared to TiCoSb. We are optimistic of the findings and believe these materials would attract experimental investigations.",2306.14234v1 2014-11-27,$Ab$ $intito$ study on some new spin-gapless semiconductors: The Zr-based quanternary Heusler alloys,"Employing $ab$ $intito$ electronic structure calculations, we have investigated electronic and magnetic properties of the Zr-based quanternary Heusler alloys: ZrCoVIn, ZrFeVGe, ZrCoFeP, ZrCoCrBe and ZrFeCrZ (Z=In and Ga). Our $ab$ $intito$ calculation results show that all the alloys are (or nearly) spin-gapless semiconductors. All the alloys have large band gaps, indicating the stability of them at room temperature. The Slater-Pauling behaviours of these alloys are discussed as well. The values of Curie temperature of all the alloys are estimated. And it is found that the values of the Curie temperature for all our calculated quanternary Heusler alloys are higher than that of room temperature.",1411.7570v2 2002-11-14,"Preparation and structural properties of thin films and multilayers of the Heusler compounds Cu2MnAl, Co2MnSn, Co2MnSi and Co2MnGe","We report on the preparation of thin films and multilayers of the intermetallic Heusler compound CuMnAl, Co2MnSn, Co2MnSi and Co2MnGe by rf-sputtering on MgO and Al2O3 substrates. Cu2MnAl can be grown epitaxially with (100)-orientation on MgO (100) and in (110)-orientation on Al2O3 a-plane. The Co based Heusler alloys need metallic seedlayers to induce high quality textured growth. We also have prepared multilayers with smooth interfaces by combining the Heusler compounds with Au and V. An analysis of the ferromagnetic saturation magnetization of the films indicates that the Cu2MnAl-compound tends to grow in the disordered B2-type structure whereas the Co-based Heusler alloy thin films grow in the ordered L21 structure. All multilayers with thin layers of the Heusler compounds exhibit a definitely reduced ferromagnetic magnetization indicating substantial disorder and intermixing at the interfaces.",0211271v1 2015-07-21,Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases,"Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of transition-group d-metals and main-group p-elements. Here, we report the realization of FSMAs in Heusler phases that completely consist of d metals. By introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is obtained and the martensitic transformation temperature is decreased efficiently. Strong ferromagnetism is established by further doping Co atoms into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the magnetic-field-induced martensitic transformations, collective multifunctional properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only facilitate the formation of B2-type Heusler phases, but also establish strong ferromagnetic coupling and offer the possibility to tune the martensitic transformation.",1507.05907v1 2015-01-03,"First-principles study of four quaternary Heusler alloys ZrMnVZ and ZrCoFeZ (Z=Si, Ge)","We investigate the electronic structure and magnetic properties of four quaternary Heusler alloys ZrMnVZ and ZrCoFeZ (Z=Si, Ge) by using first-principle calculations. It is shown that ZrMnVSi, ZrMnVGe and ZrCoFeSi are half-metallic ferromagnets with considerable half-metallic gaps of 0.14, 0.18 and 0.22 eV, respectively. ZrCoFeGe is a nearly half-metallic, the changes of properties for this alloy under pressure is investigated, the spin polarization of this alloy is 98.99\% at equilibrium lattice constant.",1501.00542v1 2010-10-14,Pressure dependence of Curie temperature and resistivity in complex Heusler alloys,"Using first-principles electronic structure calculations, we have studied the dependence of the Curie temperature on external hydrostatic pressure for random Ni2MnSn Heusler alloys doped with Cu and Pd atoms, over the entire range of dopant concentrations. The Curie temperatures are calculated by applying random-phase approximation to the Heisenberg Hamiltonian whose parameters are determined using the linear response and multiple scattering methods, based on density-functional theory. In (Ni1-x,Pdx)2MnSn alloys, the Curie temperature is found to increase with applied pressure over the whole concentration range. The crossover from the increase to the decrease of the Curie temperature with pressure takes place for Cu concentrations larger than about 70% in (Ni1-x,Cux)2MnSn Heusler alloys. The results for the reference Ni2MnSn Heusler alloy agree well with a previous theoretical study of E. Sasioglu, L. M. Sandratskii and P. Bruno Phys. Rev. B 71 214412 (2005) and also reasonably well with available experimental data. Results for the spin-disorder-induced part of the resistivity in (Ni1-x,Pdx)2MnSn Heusler alloys, calculated by using the disordered local moment model, are also presented. Finally, a qualitative understanding of the results, based on Anderson's superexchange interaction and Stearn's model of the indirect exchange interaction between localized and itinerant d electrons, is provided.",1010.3025v2 2019-03-28,Inducing half metallicity with alloying in Heusler Compound CoFeMnSb,"First principles studies were performed in order to find out the possibility of inducing half-metallicity in Heusler Compound CoFeMnSb, by means of alloying it with 3d-transition metal elements. Proper alloying element is selected through the calculations of formation energies. These calculations were tested with different concentrations of alloying elements at different atomic sites. Among the selected transition metal elements Sc and Ti are proposed to be excellent alloying elements particularly at Mn site. By using these alloying elements complete half metallic behaviour is obtained in CoFeMn0.25Sc0.75Sb, CoFeMn0.75Ti0.25Sb, CoFeMn0.625Ti0.375Sb, CoFeMn0.50Ti0.50Sb, CoFeMn0.25Ti0.75Sb and CoFeTiSb alloys. Shifting of Co-Fe d-states towards lower energy region leads to zero density of states at Fermi level for the spin minority channel. Alloying effects on the electronic structure and magnetization are discussed in details. Thermodynamical stability of these new alloys are major part of this study. The Curie temperatures of CoFeMn0.25Sc0.75Sb and CoFeMn0.75Ti0.25Sb were found to be 324.5 K and 682 K; respectively, showing good candidature for spintronics applications. For understanding the bonding nature of constituent atom of CoFeMnSb, crystal orbital Hamiltonian populations have been analysed.",1903.11799v1 2007-09-26,Role of defects and disorder in the half-metallic full-Heusler compounds,"Half-metallic ferromagnets and especially the full-Heusler alloys containing Co are at the center of scientific research due to their potential applications in spintronics. For realistic devices it is important to control accurately the creation of defects in these alloys. We review some of our late results on the role of defects and impurities in these compounds. More precisely we present results for the following cases (i) doping and disorder in Co$_2$Cr(Mn)Al(Si) alloys, (ii) half-metallic ferrimagnetism appeared due to the creation of Cr(Mn) antisites in these alloys, (iii) Co-doping in Mn$_2$VAl(Si) alloys leading to half-metallic antiferromagnetism, and finally (iv) the occurrence of vacancies in the full-Heusler alloys containing Co and Mn. These results are susceptible of encouraging further theoretical and experimental research in the properties of these compounds.",0709.4183v2 2005-07-28,Exchange interactions and temperature dependence of the magnetization in half--metallic Heusler alloys,"We study the exchange interactions in half-metallic Heusler alloys using first-principles calculations in conjunction with the frozen-magnon approximation. The Curie temperature is estimated within both mean-field (MF) and random-phase-approximation (RPA) approaches. For the half-Heusler alloys NiMnSb and CoMnSb the dominant interaction is between the nearest Mn atoms. In this case the MF and RPA estimations differ strongly. The RPA approach provides better agreement with experiment. The exchange interactions are more complex in the case of full-Heusler alloys Co$_2$MnSi and Co$_2$CrAl where the dominant effects are the inter-sublattice interactions between the Mn(Cr) and Co atoms and between Co atoms at different sublattices. For these compounds we find that both MF and RPA give very close values of the Curie temperature slightly underestimating experimental quantities. We study the influence of the lattice compression on the magnetic properties. The temperature dependence of the magnetization is calculated using the RPA method within both quantum mechanical and classical approaches.",0507697v2 2007-02-19,Defects-driven appearance of half-metallic ferrimagnetism in Co-Mn--based Heusler alloys,"Half-metallic ferromagnetic full-Heusler alloys containing Co and Mn, having the formula Co$_2$MnZ where Z a sp element, are among the most studied Heusler alloys due to their stable ferromagnetism and the high Curie temperatures which they present. Using state-of-the-art electronic structure calculations we show that when Mn atoms migrate to sites occupied in the perfect alloys by Co, these Mn atoms have spin moments antiparallel to the other transition metal atoms. The ferrimagnetic compounds, which result from this procedure, keep the half-metallic character of the parent compounds and the large exchange-splitting of the Mn impurities atoms only marginally affects the width of the gap in the minority-spin band. The case of [Co$_{1-x}$Mn$_x$]$_2$MnSi is of particular interest since Mn$_3$Si is known to crystallize in the Heusler $L2_1$ lattice structure of Co$_2$MnZ compounds. Robust half-metallic ferrimagnets are highly desirable for realistic applications since they lead to smaller energy losses due to the lower external magnetic fields created with respect to their ferromagnetic counterparts.",0702437v1 2010-02-08,Quantitative analysis of atomic disorders in full-Heusler Co2FeSi alloy thin films using x-ray diffraction with Co-Ka and Cu-Ka sources,"The authors developed a new analysis technique for atomic disorder structures in full-Heusler alloys using x-ray diffraction (XRD) with Co-Ka and Cu-Ka sources. The developed technique can quantitatively evaluate all the atomic disorders for the exchanges between X, Y, and Z atoms in full-Heusler X2YZ alloys. In particular, the technique can treat the DO3 disorder that cannot be analyzed by ordinary Cu-Ka XRD. By applying this technique to full-Heusler Co2FeSi alloy thin films formed by rapid thermal annealing (RTA), RTA-temperature (TA) dependence of the atomic disorders was revealed. The site occupancies of Co, Fe, and Si atoms on their original sites were 98 %, 90 %, and 93 %, respectively, for the film formed at TA = 800 degree C, indicating that the RTA-formed Co2FeSi film had the L21 structure with the extremely high degree of ordering.",1002.1564v1 2015-05-28,"Uncovering High Thermoelectric Figure of Merit in (Hf,Zr)NiSn Half-Heusler Alloys","Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler phases (R=Hf, Zr, Ti) are the most studied in view of their thermal stability. The highest dimensionless figure of merit (ZT) obtained is ~1 in the temperature range ~450-900oC, primarily achieved in nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an appreciable increase in the power factor, decrease in charge carrier density, and increase in carrier mobility. The findings are attributed to the improvement of structural order. Present approach may be applied to optimize the functional properties of Heusler-type alloys.",1505.07773v2 2020-04-02,Reversible adiabatic temperature change in the shape memory Heusler alloy Ni2.2Mn0.8Ga: An effect of structural compatibility,"The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory Heusler alloys put them forward to use in magnetic refrigeration technology. It is associated with a first-order magnetostructural (martensitic) phase transition. We conducted a comprehensive study of the MCE for the off-stoichiometric Heusler alloy Ni$_{2.2}$Mn$_{0.8}$Ga in the vicinity of its first-order magnetostructural phase transition. We found a reversible MCE under repeated magnetic field cycles. The reversible behavior can be attributed to the small thermal hysteresis of the martensitic phase transition. Based on the analysis of our detailed temperature dependent X-ray diffraction data, we demonstrate the geometric compatibility of the cubic austenite and tetragonal martensite phases. This finding directly relates the reversible MCE behavior to an improved geometric compatibility condition between cubic austenite and tetragonal martensite phases. The approach will help to design shape-memory Heusler alloys with a large reversible MCE taking advantage of the first-order martensitic phase transition.",2004.00949v1 2017-06-14,Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order,"Half-metallicity and low magnetic damping are perpetually sought for in spintronics materials and full Heusler alloys in this respect provide outstanding properties. However, it is challenging to obtain the well-ordered half-metallic phase in as-deposited full Heusler alloys thin films and theory has struggled to establish a fundamentals understanding of the temperature dependent Gilbert damping in these systems. Here we present a study of the temperature dependent Gilbert damping of differently ordered as-deposited Co2FeAl full Heusler alloy thin films. The sum of inter- and intraband electron scattering in conjunction with the finite electron lifetime in Bloch states govern the Gilbert damping for the well-ordered phase in contrast to the damping of partially-ordered and disordered phases which is governed by interband electronic scattering alone. These results, especially the ultralow room temperature intrinsic damping observed for the well-ordered phase provide new fundamental insights to the physical origin of the Gilbert damping in full Heusler alloy thin films.",1706.04670v2 2021-08-04,Theory of Huge Thermoelectric Effect Based on Magnon Drag Mechanism: Application to Thin-Film Heusler Alloy,"To understand the unexpectedly high thermoelectric performance observed in the thin-film Heusler alloy Fe$_2$V$_{0.8}$W$_{0.2}$Al, we study the magnon drag effect, generated by the tungsten based impurity band, as a possible source of this enhancement, in analogy to the phonon drag observed in FeSb$_2$. Assuming that the thin-film Heusler alloy has a conduction band integrating with the impurity band, originated by the tungsten substitution, we derive the electrical conductivity $L_{11}$ based on the self-consistent t-matrix approximation and the thermoelectric conductivity $L_{12}$ due to magnon drag, based on the linear response theory, and estimate the temperature dependent electrical resistivity, Seebeck coefficient and power factor. Finally, we compare the theoretical results with the experimental results of the thin-film Heusler alloy to show that the origin of the exceptional thermoelectric properties is likely to be due to the magnon drag related with the tungsten-based impurity band.",2108.01880v1 2023-05-04,Experimental observation of spin glass state in highly disordered quaternary Heusler alloy FeRuMnGa,"The realization of spin-glass (S-G) state in Heusler alloys is very rare despite the presence of inherent structural and elemental disorder in those compounds. Although a few half and full Heusler alloys are known to exhibit S-G state, there is hardly any manifestation of the same in cases of quaternary Heusler compounds. Here we report the observation of S-G state in a highly disordered equiatomic quaternary Heusler compound: FeRuMnGa, where the S-G state is in between of canonical S-G and cluster glass. Different intricate features of S-G state including non-equilibrium magnetic dynamics at low temperature in the compound are unveiled through our comprehensive magnetic, heat capacity and neutron diffraction studies. The structural disorder in the sample is neither conventional \textit{A2}- nor \textit{B2}-type while those two types are commonly observed for Heusler compounds. The presence of disorder also plays a significant role in electron transport properties of the alloy, which is reflected in its exhibition of semi-metallic behavior and anomalous Hall effect at low temperature.",2305.03093v1 2021-11-09,"Effect of substitutional doping and disorder on the phase stability, magnetism, and half-metallicity of Heusler alloys","Spintronics is the fast growing field that will play a key role in optimizing power consumption, memory, and processing capabilities of nanoelectronic devices. Heusler alloys are potential candidates for application in spintronics due to their room temperature (RT) half-metallicity, high Curie temperature, low lattice mismatch with most substrates, and strong control on electronic density of states at Fermi level. In this work, we investigate the effect of {substitutional doping and disorder} on the half-metallicity, phase stability, and magnetism of Heusler alloys using density functional theory methods. Our study shows that electronic and magnetic properties of half/full-Heusler alloys can be tuned by changing electron-count through controlled variation of chemical compositions of alloying elements. We provide a detailed discussion on the effect of substitutional doping and disorder on the tunability of half-metallic nature of Co$_{2}$MnX and NiMnX based Heusler alloys, where X represents group 13\textendash 16 and period 3\textendash 6 elements of the periodic table. {Based on the idea of electron count and disorder, we predicted a possible existence of thermodynamically stable half-metallic multicomponent bismuthides, for example, (CuNi$_{3}$)Mn$_{4}$Bi$_{4}$ and (ZnNi$_{7}$)Mn$_{8}$Bi$_{8}$, through substitution doping at Ni site by specific Cu and Zn composition in half-Heusler NiMnBi.} We believe that the design guide {based on electron-counts} presented for half-metals will play a key role in electronic-structure engineering of novel Heusler alloys for spintronic application, which will accelerate the development and synthesis of novel materials.",2111.05179v1 2016-11-24,Thermophysical and magnetic properties of p- and n-type Ti-Ni-Sn based half-Heusler alloys,"A total of 5 different half-Heusler alloys, two p-type and two n-type with the fifth a charge compensated alloy have been designed and synthesized. The thermophysical properties of these alloys have been investigated in the range 10 K to 1000 K while the magnetic behavior has been studied up to 300 K. The electrical resistivity of all the alloys varies within the range 0.06 to 5 m{\Omega} cm indicating that they are in the degenerate semiconductor limits. The temperature dependence of p-type alloys exhibits a transition from metallic to semiconducting behavior, typical of topological insulators. The transition is found to occur in the range 300 K to 500 K. The n-type and compensated alloys exhibit a weak metallic behavior in the complete temperature range. The Seebeck coefficient in the p-type alloys increases with temperature reaching a maximum value of 50 microV K-1 while that of the n-type alloys increases continuously reaching a value of 45 microV K-1 at ~ 800 K. The corresponding power factor of the n-type alloy reaches 900 microW m-1 K-2 at ~ 900 K compared to a maximum of ~ 250 microW m-1 K-2 at 700 K for the p-type alloy. Magnetically the p-type and n-type alloys are found to be paramagnetic while the compensated alloy exhibits a ferromagnetic behavior.",1611.08148v1 2014-08-19,Phase formation characteristics and magnetic properties of bulk Ni2MnGe Heusler alloy,"We have systemically studied the effects of annealing temperature and alloy composition on the structural and magnetic properties of bulk Ni$_{2}$MnGe and Ni$_{2.1}$Mn$_{0.9}$Ge Heusler alloys. We have observed that both annealing temperature and the alloy composition drastically alter the phases found in the samples due to the presence of competing ternary phases. Annealing at 900 and 950 $^{\circ}$C for both alloy compositions facilitate the formation of L2$_{1}$ Heusler phase. Nevertheless, formation of Ni$_{5}$Mn$_{4}$Ge$_{3}$ and Ni$_{16}$Mn$_{6}$Ge$_{7}$ phases cannot be prevented for Ni$_{2}$MnGe and Ni$_{2.1}$Mn$_{0.9}$Ge alloys, respectively. In order to estimate the magnetic contribution of the Ni$_{5}$Mn$_{4}$Ge$_{3}$ impurity phase to that of the parent Ni$_{2}$MnGe, we have also synthesized pure Ni$_{5}$Mn$_{4}$Ge$_{3}$ alloy. Antiferromagnetic nature of Ni$_{5}$Mn$_{4}$Ge$_{3}$ with low magnetization response allows us to reveal the magnetic response of the stoichiometric bulk Ni$_{2}$MnGe. Bulk Ni$_{2}$MnGe shows simple ferromagnetic behavior with a Curie temperature of 300 K, in agreement with the previous results on thin films. Despite the divergence of magnetization curves between field cooled (FC) and field heated (FH) modes, stoichiometric Ni$_{2}$MnGe alloy does not undergo a martensitic phase transition based on our variable temperature x-ray diffraction experiments.",1408.4241v1 2015-11-30,Band structure and transport studies of half Heusler compound DyPdBi: An efficient thermoelectric material,"The discovery of Heusler alloys has revolutionized the research field of intermetallics due to the ease with which one can derive potential candidates for multifunctional applications. During recent years, many half Heusler alloys have been investigated for their thermoelectric properties. The f electron based rare earth ternary half Heusler compound DyPdBi has its f energy levels located close to the Fermi energy level. Other research efforts have emphasized that such materials have good thermoelectric capabilities. We have explored using first principles the electronic band structure of DyPdBi by use of different exchange correlation potentials in the density functional theoretical framework. Transport coefficients that arise in the study of thermoelectric properties of DyPdBi have been calculated and illustrate its potential as an efficient thermoelectric material. Both the theoretically estimated Seebeck coefficient and the power factor agree well with the available experimental results. Our calculations illustrate that it is essential to include spin-orbit coupling in these models of f electron half Heusler materials.",1511.09187v1 2006-10-30,Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first-principles,"Half-metallic Heusler alloys are amongst the most promising materials for future magnetoelectronic applications. We review some recent results on the electronic properties of these compounds. The origin of the gap in these half-metallic alloys and its connection to the magnetic properties are well understood. Changing the lattice parameter shifts slightly the Fermi level. Spin-orbit coupling induces states within the gap but the alloys keep a very high degree of spin-polarization at the Fermi level. Small degrees of doping and disorder as well as defects with low formation energy have little effect on the properties of the gap, while temperature effects can lead to a quick loss of half-metallicity. Finally we discuss two special issues; the case of quaternary Heusler alloys and the half-metallic ferrimagnets.",0610827v1 2008-11-10,Tuning the magnetic properties of half-metallic semi-Heusler alloys by sp-electron substitution: The case of AuMnSn$_{1-x}$Sb$_x$ quaternary alloys,"We study the electronic and magnetic properties of the quaternary AuMnSn$_{1-x}$Sb$_{x}$ Heusler alloys using first principles calculations. We determine their magnetic phase diagram and we show that they present a phase transition from a ferromagnetic to an antiferromagnetic state with increasing Sb concentration. For large Sb concentrations the antiferromagnetic superexchange coupling dominates over the ferromagnetic RKKY-like exchange mechanism. This behavior is similar to the one demonstrated by the isovalent Ni$_{1-x}$Cu$_x$MnSb alloy studied recently by the authors [I. Galanakis et al, Phys. Rev. B. \textbf{77}, 214417 (2008)]. Thus the variation of the concentration of the \textit{sp}-electrons (Sn and Sb atoms) and the variation of the concentration of the non-magnetic \textit{3d} atoms (Cu) lead to a similar tuning of the the magnetic properties of the Heusler alloys. We show that the inclusion of correlation effects does not alter the phase diagram. Calculated results are in good agreement with the available experimental data.",0811.1408v1 2011-10-25,"Half-metallic properties for the Ti2YZ (Y=Fe,Co,Ni,Z=Al,Ga,In) Hesuler alloys: A first-principles study","Using the full-potential local orbital minimum-basis method,the Ti2-based full-Heusler alloys are studied. The results show that these compounds exhibit a half-metallic behavior, however, in contrast to the conventional full-Heusler alloys,the full-Heusler alloys show a Slater-Pauling behavior and the total spin magnetic moment per unit cell(Mt) following the rule Mt=Zt-18. The origin of the gap in these half-metallic alloys are well understood. It is found that the half-metallic properties of Ti2-based compounds are insensitive to the lattice distortion and a fully spin polarization can be obtained within a wide range of lattice parameters. This is favorable in practical application.",1110.5411v1 2014-10-07,"Anti-site disorder and improved functionality of Mn$_{2}$Ni{\it X} ({\it X}= Al, Ga, In, Sn) inverse Heusler alloys","Recent first-principles calculations have predicted Mn$_{2}$Ni{\it X} ({\it X}=Al, Ga, In, Sn) alloys to be magnetic shape memory alloys. Moreover, experiments on Mn$_{2}$NiGa and Mn$_{2}$NiSn suggest that the alloys deviate from the perfect inverse Heusler arrangement and that there is chemical disorder at the sublattices with tetrahedral symmetry. In this work, we investigate the effects of such chemical disorder on phase stabilities and magnetic properties using first-principles electronic structure methods. We find that except Mn$_{2}$NiAl, all other alloys show signatures of martensitic transformations in presence of anti-site disorder at the sublattices with tetrahedral symmetry. This improves the possibilities of realizing martensitic transformations at relatively low fields and the possibilities of obtaining significantly large inverse magneto-caloric effects, in comparison to perfect inverse Heusler arrangement of atoms. We analyze the origin of such improvements in functional properties by investigating electronic structures and magnetic exchange interactions.",1410.1690v1 2019-12-23,Peculiarities of electronic transport and magnetic state in half-metallic ferromagnetic and spin gapless semiconducting Heusler alloys,"A brief survey of experimental and theoretical studies of half-metallic ferromagnets (HMFs) and spin gapless semiconductors is given, the possible candidates being the X$_2$YZ (X = Mn, Fe, Co; Y = Ti, V, Cr, Mn, Fe, Co, Ni; Z = Al, Si, Ga, Ge, In, Sn, Sb) Heusler alloys. The data on the electrical resistivity, normal and anomalous Hall Effect, and magnetic properties are presented. It is shown that the Co$_2$FeZ alloys demonstrate properties of conventional ferromagnets, the HMF properties being also manifested at the variation of the Z-component. The Fe$_2$YAl and Mn$_2$YAl alloys show at the variation of the Y-component both metallic and semiconducting electronic characteristics, the magnetic properties, changing from the ferromagnetic to compensated ferrimagnetic state. The HMF and spin gapless semiconductor states are supposed to exist in these Heusler alloys systems.",1912.10771v1 2020-06-05,Anomalous dependence of thermoelectric parameters on carrier concentration and electronic structure in Mn-substituted Fe2CrAl Heusler alloy,"We investigate the high temperature thermoelectric properties of Heusler alloys Fe2-xMnxCrAl (0$ 400 K. It crystallises in the L2$_1$ structure with 50$\%$ antisite disorder between Fe and Rh. Below 300 K, it shows a weakly temperature dependent electrical resistivity with negative temperature coefficient, indicating the normal semimetal or spin semimetal behavior. Anomalous magnetoresistance data reveals dominant contribution from asymmetric part, a clear signature of spin-valve nature, which is retained even at room temperature. \textcolor{black}{The asymmetric part of magneto-resistance shows an unusual increase with increasing temperature.} Hall measurements confirm the anomalous nature of conductivity originating from the intrinsic Berry curvature, with holes being the majority carriers. Ab-initio simulation confirms a unique long-range ferrimagnetic ordering to be the ground state, explaining the origin behind the unexpected low saturation moment. The ferrimagnetic disordered structure confirms the spin semimetallic feature of FeRhCrSi, as observed experimentally.",2212.00924v2 2022-12-15,Exploration of all-3d Heusler alloys for permanent magnets: an ab initio based high-throughput study,"Heusler alloys have attracted interest in various fields of functional materials since their properties can quite easily be tuned by composition. Here, we have investigated the relatively new class of all-3d Heusler alloys in view of its potential as permanent magnets. To identify suitable candidates, we performed a high-throughput study using an electronic structure database to search for X$_2$YZ-type Heusler systems with tetragonal symmetry and high magnetization. For the alloys which passed our selection filters, we have used a combination of density functional theory calculations and spin dynamics modelling to investigate their magnetic properties including the magnetocrystalline anisotropy energy and exchange interactions. The candidates which fulfilled all the search criteria served as input for the investigation of the temperature dependence of the magnetization and determination of Curie temperature. Based on our results, we suggest that Fe$_2$NiZn, Fe$_2$NiTi and Ni$_2$CoFe are potential candidates for permanent magnets with large out-of-plane magnetic anisotropy (1.23, 0.97 and 0.82 MJ/m$^3$ respectively) and high Curie temperatures lying more than 200 K above the room temperature. We further show that the magnitude and direction of anisotropy is very sensitive to the strain by calculating the values of anisotropy energy for several tetragonal phases. Thus, application of strain can be used to tune the anisotropy in these compounds.",2212.07845v3 2017-01-28,"Half-metallicity versus Symmetry in Pt, Ni and Co-based Half Heusler Alloys: A First-principles Calculation","Using first principles calculations based on density functional theory, we study the geometric, electronic, and magnetic properties of Pt, Ni and Co-based half Heusler alloys, namely, Pt$BC$, Ni$BC$ and Co$BC$ ($B$ = Cr, Mn and Fe; $C$ = Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te). We calculate the formation energy of these alloys in various crystal symmetries, which include, the (face-centered) cubic $C1_{b}$ ($F\bar{4}$3m), orthorhombic ($Pnma$), as well as hexagonal ($P\bar{6}2m$ and $P6_{3}/mmc$) structures. It has been observed that out of all the 108 structures, studied here, energetically stable cubic structure is observed for only 18 materials. These alloys are primarily having either a $C$ atom or an $A$ atom with a high atomic number. We also observe that along with the alloys with $C$ atoms from group IIIA, IVA and VA -- alloys with $C$ atoms from group VIA are also found to be, by and large, energetically stable. To examine the relative stabilities of different symmetries in order to search for the respective lowest energy state for each of the above-mentioned systems, as well as to find whether a material in the ground state is half-metallic or not, we analyze the formation energy, and the electronic density of states, in detail. Based on these analyses, the possibility of existence of any {\it one-to-one relationship} between the {\it cubic symmetry} and the {\it half-metallicity} in these half Heusler alloys is probed. Subsequently, we predict about the existence of a few new {\it non-cubic} half Heusler alloys with substantially low density of states at one of the spin channels and reasonably {\it high spin polarization at the Fermi level}",1701.08282v2 2014-06-03,Phase coexistence and interrupted 1st order transition in magnetic shape memory alloys,"Current theoretical studies on structural and magnetic properties of functional Ni-Mn-Z (Z = Ga, In, Sn) Heusler alloys address the origin of the structural transition from the austenite to martensite, and also address the dominant contribution to the latent heat associated with this magneto-structural transition. This should help understand the origin of kinetic arrest of 1st order magnetic transitions.",1406.0627v1 2003-05-07,Appearance of Half-Metallicity in the Quaternary Heusler Alloys,"I report systematic first-principle calculations of the quaternary Heusler alloys like Co$_2$[Cr$_{1-x}$Mn$_x$]Al, Co$_2$Mn[Al$_{1-x}$Sn$_x$] and [Fe$_{1-x}$Co$_x$]$_2$MnAl. I show that when the two limiting cases (x=0 or 1) correspond to a half-metallic compound, so do the intermediate cases. Moreover the total spin moment $M_t$ in $\mu_B$ scales linearly with the total number of valence electrons $Z_t$ (and thus with the concentration $x$) following the relation $M_t=Z_t-24$, independently of the origin of the extra valence electrons, confirming the Slater-Pauling behavior of the normal Heusler alloys. Finally I discuss in all cases the trends in the atomic projected DOSs and in the atomic spin moments.",0305134v1 2009-02-09,Analysis of L21-ordering in full-Heusler Co2FeSi alloy thin films formed by rapid thermal annealing,"The authors developed a new analysis approach for evaluation of atomic ordering in full-Heusler alloys, which is extension of the commonly used Webster model. Our model can give accurate physical formalism for the degree of atomic ordering in the L21 structure, including correction with respect to the fully disordered A2 structure, i.e., the model can directly evaluate the degree of L21-ordering under a lower ordering structure than the complete B2-ordering structure. The proposed model was applied to full-Heusler Co2FeSi alloy thin films formed by rapid thermal annealing. The film formed at TA = 800 C showed a relatively high degree of L21-ordering of 83 % under a high degree of B2-ordering of 97 %.",0902.1438v1 2009-06-16,Epitaxial Growth of a Full-Heusler Alloy Co$_{2}$FeSi on Silicon by Low-Temperature Molecular Beam Epitaxy,"For electrical spin injection and detection of spin-polarized electrons in silicon, we explore highly epitaxial growth of ferromagnetic full-Heusler-alloy Co2FeSi thin films on silicon substrates using low-temperature molecular beam epitaxy (LTMBE). Although in-situ reflection high energy electron diffraction images clearly show two-dimensional epitaxial growth for growth temperatures T_G of 60, 130, and 200 C, cross-sectional transmission electron microscopy experiments reveal that there are single-crystal phases other than Heusler alloys near the interface between Co_2FeSi and Si for T_G = 130 and 200 C. On the other hand, almost perfect heterointerfaces are achieved for T_G = 60 C. These results and magnetic measurements indicate that highly epitaxial growth of Co_2FeSi thin films on Si is demonstrated only for T_G = 60 C.",0906.2840v1 2010-06-01,Observation of enhanced exchange bias behavior in NiCoMnSb Heusler alloys,"We report the observation of large exchange bias in Ni50-xCoxMn38Sb12 Heusler alloys with x=0, 2, 3, 4, 5, which is attributed to the coexistence of ferromagnetic and antiferromagnetic phases in the martensitic phase. The phase coexistence is possibly due to the supercooling of the high temperature ferromagnetic phase and the predominant antiferromagnetic component in the martensitic phase. The presence of exchange bias is well supported by the observation of training effect. The exchange bias field increases with Co concentration. The maximum value of 480 Oe at T=3K is observed in x=5 after field cooling in 50 kOe, which is almost double the highest value reported so far in any Heusler alloy system. Increase in the antiferromagnetic coupling after Co substitution is found to be responsible for the increase in the exchange bias.",1006.0071v1 2012-06-11,Crossover from antiferromagnetic to ferromagnetic ordering in semi-Heusler alloys Cu1-xNixMnSb with increasing Ni concentration,"The magnetic properties and transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state in semi Heusler alloys Cu1-xNixMnSb, with x < 0.3 have been investigated in details by dc magnetization, neutron diffraction, and neutron depolarization. We observe that for x < 0.05, the system Cu1-xNixMnSb is mainly in the AFM state. In the region 0.05 \leq x \leq 0.2, with decrease in temperature, there is a transition from a paramagnetic to a FM state and below ~50 K both AFM and FM phases coexist. With an increase in Ni substitution, the FM phase grows at the expense of the AFM phase and for x > 0.2, the system fully transforms to the FM phase. Based on the results obtained, we have performed a quantitative analysis of both magnetic phases and propose a magnetic phase diagram for the Cu1-xNixMnSb series in the region x < 0.3. Our study gives a microscopic understanding of the observed crossover from the AFM to FM ordering in the studied semi Heusler alloys Cu1-xNixMnSb.",1206.2243v1 2013-11-22,Full-Heusler Co2FeSi alloy thin films with perpendicular magnetic anisotropy induced by MgO-interface,"The authors demonstrated that L21-ordered full-Heusler Co2FeSi (CFS) alloy film with thickness of 100 nm were formed by facing targets sputtering (FTS) method at a substrate temperature TS = 300 deg C. Degrees of L21- and B2- order for the film were 0.37, and 0.96, respectively. Furthermore, full-Heusler CFS alloy thin films with perpendicular magnetic anisotropy (PMA) induced by MgO-interface magnetic anisotropy were successfully formed by the FTS method. The CFS/MgO stacking layers showed PMA when dCFS was 0.6 nm <= dCFS <= 1.0 nm. The PMA in these structures resulted from the CFS/MgO interfacial perpendicular magnetic anisotropy.",1311.5670v2 2015-08-07,Multifunctional Heusler alloy: experimental evidences of enhanced magnetocaloric properties at room temperature and half-metallicity,"Heusler alloys are widely studied due to their interesting structural and magnetic properties, like magnetic memory shape ability, coupled magneto-structural phase transitions and half-metallicity; ruled, for many cases, by the valence electrons number ($N_v$). The present work focuses on the magnetocaloric potentials of half-metals, exploring the effect of $N_v$ on the magnetic entropy change, preserving half-metallicity. The test bench is the Si-rich side of the half-metallic series Fe$_2$MnSi$_{1-x}$Ga$_x$. From the obtained experimental results it was possible to obtain $|\Delta S|_{max}=\Delta H^{0.8}(\alpha+\beta N_v)$, i.e., the maximum magnetic entropy change depends in a linear fashion on $N_v$, weighted by a power law on the magnetic field change $\Delta H$ ($\alpha$ and $\beta$ are constants experimentally determined). In addition, it was also possible to predict a new multifunctional Heusler alloy, with enhanced magnetocaloric effect, Curie temperature close to 300 K and half-metallicity.",1508.01828v1 2018-09-19,Quaternary Heusler Alloy: An Ideal Platform to Realize Triple Point Fermion,"The existence of three fold rotational, mirror and time reversal symmetries often give rise to the triply degenerate nodal point (TP) in the band structure of a material. Based on point group symmetry analysis and first principle electronic structure, we predict, in this article, a series of quaternary Heusler alloys host an ideal platform for the occurrence of TP. We simulated, the projection of these TPs onto the (111) and (100) surfaces lead to form topological Fermi arcs, which may further be detected by scanning tunneling spectroscopy and angle resolved photoemission spectroscopy. These Fermi arcs arise due to the symmetry protected band degeneracies, which are robust and can not be avoided due to the non-trivial band topology. Interestingly the TPs, in these class of Heusler alloys are far away from the $\Gamma$ point along C$_3$ axes, which allow to overcome the experimental difficulties over previously studied hexagonal and HgTe-type compounds.",1809.07026v1 2019-11-22,Superconducting spin-valve effect in heterostructures with ferromagnetic Heusler alloy layers,"We report a comparative analysis and theoretical description of the superconducting properties of two spin-valve-valve structures containing the Heusler alloy Co$_2$Cr$_{1-x}$Fe$_x$Al$_{y}$ as one of two ferromagnetic (F1 or F2) layers of the F1/F2/S structure, where S stands for the superconducting Pb layer. In our experiments we used the Heusler alloy layer in two roles: as a weak ferromagnet on the place of the F2 layer and as a half-metal on the place of the F1 layer. In the first case, we obtained a large ordinary superconducting spin-valve effect $\Delta T_c$ assisted by the triplet superconducting spin-valve effect $\Delta T_c^{trip}$. In the second case, we observed a giant magnitude of $\Delta T_c^{trip}$ reaching 0.5 K. An underlying theory based on the solution of the Usadel equations using Kupriyanov-Lukichev boundary conditions with arbitrary material parameters for all layers and arbitrary boundary parameters for all interfaces is presented in Appendix. We find a good agreement between our experimental data and theoretical results.",1911.09984v1 2017-04-03,Half-Heusler alloy LiBaBi: A new topological semimetal with five-fold band degeneracy,"Based on first-principles study, we report the finding of a new topological semimetal LiBaBi in half-Heusler phase. The remarkable feature of this nonmagnetic, inversion-symmetry-breaking material is that it consists of only simple $s$- and $p$-block elements. Interestingly, the material is ordinary insulator in the absence of spin-orbit coupling (SOC) and becomes nodal-surface topological semimetal showing drumhead states when SOC is included. This is in stark contrast to other nodal-line and nodal-surface semimetals, where the extended nodal structure is destroyed once SOC is included. Importantly, the linear band crossings host three-, four-, five- and six-fold degeneracies near the Fermi level, making this compound very attractive for the study of `unconventional' fermions. The band crossing points form a three-dimensional nodal structure around the zone center at the Fermi level. We identify the surface states responsible for the appearance of the drumhead states. The alloy also shows a phase transition from topological semimetal to a trivial insulator on application of pressure. In addition to revealing an intriguing effect of SOC on the nodal structure, our findings introduce a new half-Heusler alloy in the family of topological semimetals, thus creating more avenues for experimental exploration.",1704.00697v1 2018-07-17,Ferromagnetically correlated clusters in semi-metallic Ru2NbAl Heusler alloy,"In this work, we report the structural, magnetic and electrical and thermal transport properties of the Heusler-type alloy Ru2NbAl. From the detailed analysis of magnetization data, we infer the presence of superparamagnetically interacting clusters with a Pauli paramagnetic background, while short-range ferromagnetic interaction is developed among the clusters below 5 K. The presence of this ferromagnetic interaction is confirmed through heat capacity measurements. The relatively small value of electronic contribution to specific heat, gamma (~2.7 mJ/mol-K2), as well as the linear nature of temperature dependence of Seebeck coefficient indicate a semi-metallic ground state with a pseudo-gap that is also supported by our electronic structure calculations. The activated nature of resistivity is reflected in the observed negative temperature coefficient and has its origin in the charge carrier localization due to antisite defects, inferred from magnetic measurements as well as structural analysis. Although the absolute value of thermoelectric figure of merit is rather low (ZT = 5.2*10-3) in Ru2NbAl, it is the largest among all the reported non-doped full Heusler alloys.",1807.06608v1 2019-04-25,Low damping magnetic properties and perpendicular magnetic anisotropy with strong volume contribution in the Heusler alloy Fe1.5CoGe,"We present a study of the dynamic magnetic properties of TiN-buffered epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series annealed at different temperatures are prepared and the magnetic damping is measured, a lowest value of $\alpha=2.18\times 10^{-3}$ is obtained. The perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also characterized. The evolution of the interfacial perpendicular anisotropy constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and compared with the widely used CoFeB/MgO interface. A large volume contribution to the perpendicular anisotropy of $(4.3\pm0.5)\times 10^{5}$ $\rm J/m^3$ is also found, in contrast with vanishing bulk contribution in common Co- and Fe-based Heusler alloys.",1904.11247v1 2018-02-07,"Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy","Future spintronics requires the realization of thin film of half-metallic ferromagnets having high Curie temperature and 100\% spin polarization at the Fermi level for potential spintronics applications. In this paper, we report the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO (001) substrate using pulsed laser deposition system, along with the study of structural, magnetic and transport properties. The magnetic property measurements of the thin film suggest a soft ferromagnetic state at room temperature with an in-plane magnetic anisotropy and a Curie temperature well above the room temperature. Anisotropic magnetoresistance (AMR) ratio and temperature dependent electrical resistivity measurements of the thin film indicate the compound to be half-metallic in nature and therefore suitable for the fabrications of spintronics devices.",1802.02413v1 2018-02-17,FeTaSb and FeMnTiSb as promising thermoelectric materials: An ab initio approach,"Thermoelectricity in principle provides a pathway to put waste heat to good use. Motivated by this we investigate thermal and electrical transport properties of two new Fe-based Heusler alloys, FeTaSb and FeMnTiSb, by a first principles approach and semiclassical Boltzmann transport theory within the constant relaxation-time approximation. We find a high power factor of \textit{p}-doped FeTaSb, competitive with best performing Heusler alloy FeNbSb at 1100 K. The obtained power factor of \textit{n}-doped FeMnTiSb at room temperature is higher than that of both FeNbSb and FeTaSb. Remarkably, FeMnTiSb can be used for both \textit{n}-type and \textit{p}-type legs in a thermoelectric module. The Seebeck coefficients of the two proposed systems are in line with those of earlier reported Heusler alloys. We also provide conservative estimates of the figure of merit for the two systems. Overall, our findings suggest a high temperature thermoelectric potential of FeTaSb while the low cost FeMnTiSb is a viable room temperature thermoelectric candidate material.",1802.06254v1 2018-12-13,Current-induced nucleation and dynamics of skyrmions in a Co-based Heusler alloy,"We demonstrate room-temperature stabilization of dipolar magnetic skyrmions with diameters in the range of $100$ nm in a single ultrathin layer of the Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy magnetometer operating in the photoluminescence quenching mode. We first demonstrate skyrmion nucleation by spin-orbit torque and show that its efficiency can be significantly improved using tilted magnetic fields, an effect which is not specific to Heusler alloys and could be advantageous for future skyrmion-based devices. We then show that current-induced skyrmion motion remains limited by strong pinning effects, even though CFA is a magnetic material with a low magnetic damping parameter.",1812.05345v1 2020-04-03,Improved magnetostructural and magnetocaloric reversibility in magnetic Ni-Mn-In shape-memory Heusler alloy by optimizing the geometric compatibility condition,"We report an improved reversibility of magnetostriction and inverse magnetocaloric effect (MCE) for the magnetic shape-memory Heusler alloy Ni$_{1.8}$Mn$_{1.8}$In$_{0.4}$. We show that the magnetostriction and MCE crucially depends on the geometrical compatibility of the austenite and martensite phases. Detailed information on the compatibility of both phases has been obtained from the transformation matrix calculated from x-ray diffraction data. The uniqueness of the lattice parameters results in an improved reversibility of the magnetostriction and the MCE. In the thermal hysteresis region of the martensitic transformation, the maximum relative length change is 0.3% and the adiabatic temperature change $\Delta T_{ad}\approx -10$ K in pulsed magnetic fields. Our results reveal that the approach of geometric compatibility will allow one to design materials with reversible magnetostriction and reversible inverse MCE at a first-order magnetostructural phase transition in shape-memory Heusler alloys.",2004.01527v1 2019-08-20,Coexistence of spin frustration and spin unfrustration induced spontaneous exchange bias in Heusler alloys,"The mechanism of spontaneous exchange bias (SEB) and the dominant factor of its blocking temperature are still unclear in Heusler alloys. Here, the related investigations are performed in Mn2Ni1.5Al0.5 Heusler alloys with SEB. The results of both magnetic measurements and first-principles calculations confirmed that spin frustrated and unfrustrated antiferromagnetic (AFM) states coexist there and they have different magnetic anisotropies, which are essential for SEB. Based on a series of measurement strategies, we demonstrate that the frustrated AFM state undergoes a first-order magnetic transition to the superferromagnet (SFM) state with the help of an external magnetic field, and SFM is retained due to the first-order property of the magnetic transition. SEB originates from the interface coupling of multiple sublattices between the unfrustrated AFM state and SFM state. By analyzing the Arrott plot using the Landau model, we found that the internal field of the system dominates the blocking temperature of SEB, which paves the way for improving the blocking temperature.",1908.07149v1 2020-09-09,"Structural, Elastic, Electronic and Magnetic Properties of MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) Semi-Heusler Alloys","The study of structural, electronic, magnetic, and elastic properties of new series of semi-Heusler alloys MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) has been performed by density functional theory. The magnetic phase and hence the structural stability of the alloys were considered wherein ferromagnetic state is found to stable. The half-metallic states are observed from the density of states and band structure calculations. The total magnetic moments found for all studied compounds are 1 $\mu_B$/f.u., which obey Slating-Pauling rule for semi-Heusler with ferromagnetic behavior. The calculated elastic constant C$_{ij}$, cohesive energy, and formation energy confirmed that these materials are mechanically stable. Among the four system, MnNbAs is found to have the highest ductility while the remaining systems are found to be brittle in nature. These properties confirmed that among others, MnNbAs is one of the novel candidate for spintronic devices applications.",2009.04123v1 2020-12-22,"Structural insight using anomalous XRD into Mn2CoAl Heusler alloy films grown by magnetron sputtering, IBAS and MBE techniques","Inverse Heusler alloy Mn2CoAl thin films, known as a spin-gapless semiconductor (SGS), grown by three different methods: ultra-high vacuum magnetron spattering, Ar-ion beam assisted sputtering, and molecular beam epitaxy, are investigated by comparing their electric transport properties, microstructures and atomic-level structures. Of the samples, the Mn2CoAl thin film grown by MBE consists of Mn- and Co-rich phases, the structures of which are determined to be the L21B-type and disordered L21-type, respectively, according to anomalous XRD analysis. None of them forms the XA-type structure expected for SGS Heusler alloy, although they all show SGS characteristics. We suggest, to validate SGS characteristics, it is necessary to extract not only magnetic and electric transport properties but also information about microstructures and atomic-scale structures of the films including defects such as atomic swap.",2012.12282v1 2021-02-01,"Electronic, magnetic and galvanomagnetic properties of Co-based Heusler alloys: possible states of a half-metallic ferromagnet and spin gapless semiconductor","Parameters of the energy gap and, consequently, electronic, magnetic and galvanomagnetic properties in different X$_2$YZ Heusler alloys can vary quite strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless semiconductors (SGSs) with almost 100% spin polarization of charge carriers are promising materials for spintronics. The changes in the electrical, magnetic and galvanomagnetic properties of the Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and Co$_2$MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF and/or SGS states were followed and their interconnection was established. Significant changes in the values of the magnetization and residual resistivity were found. At the same time, the correlations between the changes in these electronic and magnetic characteristics depending on the number of valence electrons and spin polarization are observed.",2102.00952v1 2021-09-23,Tuning magnetic antiskyrmion stability in tetragonal inverse Heusler alloys,"The identification of materials supporting complex, tunable magnetic order at ambient temperatures is foundational to the development of new magnetic device architectures. We report the design of Mn2XY tetragonal inverse Heusler alloys that are capable of hosting magnetic antiskyrmions whose stability is sensitive to elastic strain. We first construct a universal magnetic Hamiltonian capturing the short- and long- range magnetic order which can be expected in these materials. This model reveals critical combinations of magnetic interactions that are necessary to approach a magnetic phase boundary, where the magnetic structure is highly susceptible to small perturbations such as elastic strain. We then computationally search for quaternary Mn2(X1,X2)Y alloys where these critical interactions may be realized and which are likely to be synthesizable in the inverse Heusler structure. We identify the Mn2Pt(1-z)X(z)Ga family of materials with X=Au, Ir, Ni as an ideal system for accessing all possible magnetic phases, with several critical compositions where magnetic phase transitions may be actuated mechanically.",2109.11423v1 2007-07-03,Effect of Co and Fe on the inverse magnetocaloric properties of Ni-Mn-Sn,"At certain compositions Ni-Mn-$X$ Heusler alloys ($X$: group IIIA-VA elements) undergo martensitic transformations, and many of them exhibit inverse magnetocaloric effects. In alloys where $X$ is Sn, the isothermal entropy change is largest among the Heusler alloys, particularly in Ni$_{50}$Mn$_{37}$Sn$_{13}$ where it reaches a value of 20 Jkg$^{-1}$K$^{-1}$ for a field of 5T. We substitute Ni with Fe and Co in this alloy, each in amounts of 1 at% and 3 at% to perturb the electronic concentration and examine the resulting changes in the magnetocaloric properties. Increasing both Fe and Co concentrations causes the martensitic transition temperature to decrease, whereby the substitution by Co at both compositions or substituting 1 at% Fe leads to a decrease in the magnetocaloric effect. On the other hand, the magnetocaloric effect in the alloy with 3 at% Fe leads to an increase in the value of the entropy change to about 30 Jkg$^{-1}$K$^{-1}$ at 5T.",0707.0360v1 2015-01-21,"Antiferromagnetism in Ru2MnZ (Z=Sn, Sb, Ge, Si) full Heusler alloys: effects of magnetic frustration and chemical disorder","We present systematic theoretical investigations to explore the microscopic mechanisms leading to the formation of antiferromagnetism in Ru2MnZ (Z= Sn,Sb,Ge,Si) full Heusler alloys. Our study is based on first-principles calculations of inter-atomic Mn-Mn exchange interactions to set up a suitable Heisenberg spin-model and on subsequent Monte-Carlo simulations of the magnetic properties at finite temperature. The exchange interactions are derived from the paramagnetic state, while a realistic account of long-range chemical disorder is made in the framework of the Coherent Potential Approximation. We find that in case of the highly ordered alloys (Z=Sn and Sb) the exchange interactions derived from the perfectly ordered L21 structure lead to N\'eel temperatures in excellent agreement with the experiments, whereas, in particular, in case of Si the consideration of chemical disorder is essential to reproduce the experimental N\'eel temperatures. Our numerical results suggest that improving a heat treatment of the samples to suppress the intermixing between the Mn and Si atoms, the N\'eel temperature of the Si-based alloys can potentially be increased by more than 30%. Furthermore, we show that in strongly disordered Ru2MnSi alloys a distinct change in the antiferromagnetic ordering occurs.",1501.05116v1 2015-06-10,A first-principle study of half-Heusler alloys CKMg and SiKMg,"The structural, electronic, and magnetic properties of half-Heusler alloys CKMg and SiKMg are studied by using first-principle density functional theory. The calculations reveal the SiKMg alloy is a half-metallic ferromagnet with the magnetic moment of 1 $\mu_B$ per formula unit at equilibrium lattice constant. The magnetic moment mainly originates from the strong spin-polarization of $p$ electrons of Si atom and partial involvement of $d$ electrons of K atom. The half-metallic gap is 0.105 eV. The robustness of half-metallic against the lattice constants for SiKMg is also calculated. CKMg alloy is nearly half-metallic with a spin polarization of 99.99 \%\ at equilibrium lattice constant, but it is a good half-metallic alloy when a low pressure is applied. This shows CKMg is a very promising spintronic functional material.",1506.03297v1 2015-09-16,Structural and magnetic properties of a new and ordered quaternary alloy MnNiCuSb (SG: F-43m),"We have synthesized a new crystallographically ordered quaternary Heusler alloy, MnNiCuSb. The crystal structure of the alloy has been determined by Rietveld refinement of the powder x-ray diffraction data. This alloy crystallizes in the LiMgPdSb type structure with F-43m space group. MnNiCuSb is a ferromagnet with a high TC ~ 690K and magnetic moment of 3.85MuB/f.u. Besides this we have also studied two other off-stoichiometric compositions; one Cu rich and the other Ni rich (MnNi0.9Cu1.1Sb and MnNi1.1Cu0.9Sb) which are also ferromagnets. It must be stressed that MnNiCuSb is one of the very few known, non-Fe containing quaternary Heusler alloys with 1: 1: 1: 1 composition.",1509.04833v1 2022-05-07,First-principle calculations on Li2CuSb: A novel material for lithium-ion batteries,"We investigate the Li2CuSb full-Heusler alloy using the first-principles electronic structure calculations and propose the electrochemical lithiation in this alloy. Band structure calculations suggest the presence of metallic nature in this alloy contrary to half-metallic nature as predicted for most of the members of the full-Heusler alloy family. This alloy is found to be a promising anode material for high-capacity rechargeable batteries based on lithium-ion. We found a removal voltage of 2.48 V for lithium ions in the Li2CuSb/Cu cell, which is in good agreement with the experimentally obtained result for a similar kind of material Cu3Sb. During charge and discharge cycles of the Li2CuSb/Cu cell, the formation of a non-stoichiometric compound Li2-yCu1+xSb having a similar structure as Li2CuSb suggests a better performance as well as stabilitty of this cell.",2205.03631v1 2020-07-15,Experimentally correlating thermal hysteresis and phase compatibility in multifunctional Heusler alloys,"Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural and magnetic properties of the Ni2Mn1-xCuxGa0.84Al0.16 Heusler alloys. The alloys present a thermal hysteresis reduction of ~60% when the Cu content in the compound varies from x = 0.10 to x = 0.25, with a minimum hysteresis width of 6 K being achieved. We applied the geometric non-linear theory of martensite to address the phase compatibility, quantified by the parameter lambda2, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (lambda2 closer to 1) between the austenite and martensite phases. In addition, we show that the valley-like properties of hysteresis found in the Ni2Mn1-xCuxGa0.84Al0.16 compounds is present in several other alloys in the literature. These results provide new pathways to understand as well as to masters the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys.",2007.07485v1 2023-05-04,4d-element induced improvement of structural disorder and development of weakly re-entrant spin-glass behaviour in NiRuMnSn,"The pursuit of efficient spin-polarization in quaternary Heusler alloys with the general formula $XX'YZ$ (where X, $X'$, and Y are transition metals and Z is a p-block element), has been a subject of significant scientific interest. While previous studies shows that isoelectronic substitution of 4d element in place of 3d element in quaternary Heusler alloy, improves the half-metallic ferromagnetic characteristics, our research on the quaternary Heusler alloy NiRuMnSn reveals a strikingly different scenario. In this study, we present a detailed structural analysis of the material using X-ray absorption fine structure (EXAFS) and neutron diffraction (ND) techniques, which confirms the formation of a single-phase compound with 50:50 site disorder between Ni/Ru atoms at 4c/4d sites. Contrary to expectations, our DFT calculations suggests a considerable decrease in spin-polarization even in the ordered structure. Additionally, we report on the compound's exceptional behavior, displaying a rare re-entrant spin glass property below $\sim$60 K, a unique and intriguing feature for quaternary Heusler-type compounds.",2305.03087v1 2012-10-22,"Structure, magnetism and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys","The structure, magnetism, magnetic compensation behavior, exchange interaction and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 (x=0-25) alloys have been systematically investigated by both experiments and first-principles calculations. We found that all the samples exhibited body centered cubic structures with a high degree of atomic ordering. With increasing Ga content, the composition dependence of lattice parameters shows a kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be attributed to the enhanced covalent effect between the Ga and the transition metals. Furthermore, a complicated magnetic competition has been revealed in Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically decrease and results in a magnetic moment compensation behavior. In Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional ferrimagnetic configuration was established in the native ferromagnetic matrix, which causes the molecular moment monotonously decreases and the exchange interaction enhances gradually. The electronic structure calculations indicate that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the itinerant and localized magnetism. Our study will be helpful to understand the nature of magnetic ordering as well as to tune magnetic compensation and electronic properties of Heusler alloys.",1210.5810v1 2019-02-20,Effect of the temperature and magnetic field induced martensitic transformation in bulk Fe$_{45}$Mn$_{26}$Ga$_{29}$ alloy on its electronic structure and physical properties,"Effect of the temperature and magnetic field induced martensitic transformation (MT) on the electronic structure and some physical properties of bulk Fe$_{45.2}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy has been investigated. {According to the experimental results of DSC, magnetic and transport measurements direct and reverse martensitic transformation without external magnetic field takes place within 194 $\leq T \leq$ 328 K temperature range with a hysteresis up to $\Delta T \approx$ 100 K defined as $\Delta T$ = $A_{f,s}$ - $M_{s,f}$, where $A_{f,s}$ and $M_{s,f}$ are the critical temperatures of direct and reverse martensitic transformation. External magnetic field of $\mu_{0}H$ = 5 T causes a high-temperature shift of MT temperatures.} MT from parent austenite L2$_{1}$ phase to martensitic tetragonally distorted L2$_{1}$ one (i. e. to L1$_{0}$) causes significant changes in the electronic structure of alloy, a drastic increase in alloy magnetization, a decrease in the alloy resistivity, and a reversal of the sign of the temperature coefficient of resistivity from negative to positive. At the same time experimentally determined optical properties of Fe$_{45.6}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy in austenitic and martensitic states look visually rather similar being noticeable different in microscopic nature as can be concluded from first-principle calculations. Experimentally observed changes in the physical properties of the alloy are discussed in terms of the electronic structures of an austenite and martensite phases.",1902.07462v1 2007-06-29,"Role of the exchange and correlation potential into calculating the x-ray absorption spectra of half-metallic alloys: the case of Mn and Cu K-edge XANES in Cu$_2$MnM (M = Al, Sn, In) Heusler alloys","This work reports a theoretical study of the x-ray absorption near-edge structure spectra at both the Cu and the Mn K-edge in several Cu$_2$MnM (M= Al, Sn and In) Heusler alloys. Our results show that {\it ab-initio} single-channel multiple-scattering calculations are able of reproducing the experimental spectra. Moreover, an extensive discussion is presented concerning the role of the final state potential needed to reproduce the experimental data of these half-metallic alloys. In particular, the effects of the cluster-size and of the exchange and correlation potential needed in reproducing all the experimental XANES features are discussed.",0706.4370v3 2011-04-21,"Effect of Fe substitution on the magnetic, transport, thermal and magnetocaloric properties in Ni50Mn38-xFexSb12 Heusler alloys","The structural, magnetic, transport, thermal and magnetothermal properties of quaternary Heusler alloys Ni50Mn38-xFexSb12 have been studied. Powder x-ray diffraction and temperature dependence of magnetization studies reveal that with addition of Fe in Mn site, the martensitic transition shifts to lower temperatures. It is also found that the martensitic transition becomes broader for the higher Fe concentrations. The metamagnetic transition in M(H) isotherms becomes very prominent in x=2 and vanishes for x=3 and 4. A maximum positive magnetic entropy change of 14.2 J/kg K is observed for x=2 at 288 K for 50 kOe. Resistivity shows an abrupt decrease across the martensitic transition in all the alloys, except x=6, which does not have the martensitic transition. Maximum negative magnetoresistance of 21% has been obtained for x=2 at 50 kOe. The same alloy also shows an exchange bias field of 288 Oe.",1104.4214v1 2012-12-08,$Ab~initio$ studies of Co$_2$FeAl$_{1-x}$Si$_x$ Heusler alloys,"We present results of extensive theoretical studies of Co$_2$FeAl$_{1-x}$Si$_x$ Heusler alloys, which have been performed in the framework of density functional theory employing the all-electron full-potential linearized augmented plane-wave scheme. It is shown that the Si-rich alloys are more resistive to structural disorder and as a consequence Si stabilizes the $L2_1$ structure. Si alloying changes position of the Fermi level, pushing it into the gap of the minority spin-band. It is also shown that the hyperfine field on Co nuclei increases with the Si concentration, and this increase originates mostly from the changes in the electronic density of the valence electrons.",1212.1781v2 2013-07-08,Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds,"Half-Heusler (HH) alloys have attracted considerable interest as promising thermoelectric (TE) materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties of HH alloys. Next, we review the details of HH nanocomposites as obtained by different techniques. Finally, the review closes by highlighting several promising strategies for further research directions in these very promising TE materials.",1307.2156v1 2015-10-17,Direct evidence for minority spin gap in the Co2MnSi Heusler alloy,"Half Metal Magnets are of great interest in the field of spintronics because of their potential full spin-polarization at the Fermi level and low magnetization damping. The high Curie temperature and predicted 0.7eV minority spin gap make the Heusler alloy Co2MnSi very promising for applications.We investigated the half-metallic magnetic character of this alloy using spin-resolved photoemission, ab initio calculation and ferromagnetic resonance. At the surface of Co2MnSi, a gap in the minority spin channel is observed, leading to 100% spin polarization. However, this gap is 0.3 eV below the Fermi level and a minority spin state is observed at the Fermi level. We show that a minority spin gap at the Fermi energy can nevertheless be recovered either by changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi or MgO. This results in extremely small damping coefficients reaching values as low as 7x 10-4.",1510.05085v1 2018-02-28,Magnetocaloric effect in some magnetic materials in alternating magnetic fields up to 22 Hz,"Direct measurements of the magnetocaloric effect (MCE) in different materials (Gd, Fe48Rh52, Ni43Mn37.9In12.1Co7 and Ni2.07Co0.09Mn0.84Ga) in alternating magnetic fields with frequencies f < 22 Hz and an amplitude deltaH = 6.2 kOe are carried out. The MCE in Gd shows inconsiderable changes with field frequency. Near paramagnetic-ferromagnetic phase transition in Ni43Mn37.9In12.1Co7 Heusler alloy a slight reduction of MCE with frequency is observed. In weak alternating fields in materials with AFM-FM magneto-structural phase transitions (Fe48Rh52, Ni43Mn37.9In12.1Co7) it is not possible to get a structural contribution to overall MCE because of irreversibility of the transitions in these fields. Near magneto-structural phase transitions the MCE in these alloys has only magnetic contribution, and does not show a significant dependence on the magnetic field frequency. In Ni2.07Co0.09Mn0.84Ga Heusler alloy the MCE vanishes at frequencies about 20 Hz. The obtained results show the increase of frequencies of operating cycles is one of the powerful methods to improve the efficiency of magnetic refrigerators in case of Gd as a refrigerant.",1802.10391v1 2020-04-13,Half-metallic compositional ranges for selected Heusler alloys,"For a material that is a half-metal, there should exist a range of compositions for half-metallicity. This compositional range can be expressed in terms of electron count and computed. We investigate electronic and magnetic properties of doped full- and half-Heusler alloys (stoichiometry XYZ2 and XYZ, respectively) with elements X from groups 13-16 and periods 3-6 of the Periodic Table, Y={Mn, Fe}, and Z={Co, Ni}. Using spin density functional theory, we predict shifts of the Fermi energy in the doped and solid-solution alloys. These predictions can be used for band-gap engineering of multicomponent half-metals and provide the viable range of compositions, such as for a range of n=x+y+z in (Co$_{2-z}Ni_z)$(Mn$_{1-y}$Fe$_{y}$)(Sn$_{1-x}$Sb$_{x}$). This methodology for doped and chemically disordered half-metallic alloys offers a design approach to electronic-structure engineering that can accelerate development of half-metals for novel electronic and spintronic applications.",2004.06233v1 2016-12-21,Volume dependence of magnetic properties in Co2Cr1-xYxGa (Y=Ti-Ni) Heusler alloys: a first-principles study,"The magnetic properties tuning and volume dependence in the series of quaternary full Heusler alloys with formula Co2Cr1-xYGa (Y = Ti, V, Mn, Fe, Co, Ni) were studied with a detailed first-principles exploration. We employ the density functional KKR method with the coherent potential approximation, estimating effective Heisenberg exchange constants via the magnetic force theorem together with mean-field Curie temperature (TC) and magnetic moment for compositions in the whole concentration range. The volumetric dependency of these magnetic properties is studied, particularly the pressure derivatives of TC at equilibrium. Our ternary alloy calculations show good agreement with local-density and generalized gradient approximations in the literature. The quaternary alloys show a wide range of tunable magnetic properties, where magnetic moments range from 0.8 to 4.9 mu_B, TC from 130 K to 1250 K, and dTC/dV values range from -7 to +6.3 K A-3.",1612.07071v1 2017-10-07,Effect of multinary substitution on electronic and transport properties of TiCoSb based half-Heusler alloys,"The electronic structures of TixZrx/2CoPbxTex, TixZrx/2Hfx/2CoPbxTex (x = 0.5), and the parent compound TiCoSb were investigated using the full potential linearized augmented plane wave method. The thermoelectric transport properties of these alloys are calculated on the basis of semi-classical Boltzmann transport theory. From the band structure calculations we show that the substitution of Zr,Hf in the Ti site and Pb and Te in the Sb site lower the band gap value and also change the indirect band (IB) gap of TiCoSb to the direct band (DB) gap. The calculated band gap of TiCoSb, TixZrx/2CoPbxTex, and TixZrx/2Hfx/2CoPbxTex are 1.04 eV (IB), 0.92 eV (DB), and 0.93 eV (DB), respectively. All these alloys follow the empirical rule of 18 valence-electron content which is essential for bringing semiconductivity in half Heusler alloys. It is shown that the substitution of Hf at the Ti site improve the ZT value (~1.05) at room temperature, whereas there is no significant difference in ZT is found at higher temperature. Based on the calculated thermoelectric transport properties, we conclude that the appropriate concentration of Hf substitution can further improve the thermoelectric performance of TixZrx/2Hfx/2CoPbxTex.",1710.02639v1 2020-10-19,"Investigation on structural, electronic and magnetic properties of Co2FeGe Heusler alloy: experiment and theory","Experimental and computational studies were performed on Co2FeGe Heusler alloy. It was found that the alloy has very high experimental magnetic moment of 6.1 muB/f.u., curie temperature of 1073K and very high spin-wave stiffness constant of 10.4 nm2-meV, which indicates that the magnetic moment is very high and do not vary with change in temperature in the range 0-300K. The alloy strictly follows Slater-Pauling (SP) rule and the minor experimental deviation from its SP value is justified by doing full-potential density functional calculations which gives more accurate result when electron-electron correlation parameter (U) is taken into account with conventional GGA method. Effect of lattice strain and electron correlation on individual atomic moments, total magnetic moment and spin-polarization is studied in detail and can be concluded that they have a role in the deviation of the experimental results from the expected theoretical values.",2010.09590v1 2021-06-18,Atomistic spin model of single pulse toggle switching in Mn$_2$Ru$_x$Ga Heusler alloys,"Single femtosecond pulse toggle switching of ferrimagnetic alloys is an essential building block for ultrafast spintronics. Very different element-specific demagnetization dynamics is believed to be a hard limit for switching in ferrimagnets. This suggests that ferrimagnets composed of two ions of different nature, such as rare earth transition metal alloys, are necessary for switching. However, experimental observation of toggle switching in Mn$_2$Ru$_x$Ga Heusler alloys, has contested this limit since Mn ions are of the same nature. To shed some light into this question, we present an atomistic spin model for the simulation of single pulse toggle switching of Mn$_2$Ru$_x$Ga. The magnetic parameters entering in our model are extracted from previous experimental observations. We show that our model is able to quantitatively reproduce measured magnetization dynamics of single pulse toggle switching. We demonstrate that differently to previous understanding toggle switching in Mn$_2$Ru$_x$Ga is possible even when both Mn sublattices demagnetization at very similar rate.",2106.10111v2 2021-07-24,Randomly packed Ni$_2$MnIn and NiMn structural units in off stoichiometric Ni$_2$Mn$_{2-y}$In$_y$ alloys,"Ni$_2$Mn$_{2-y}$In$_y$ alloys transform from the martensitic $L1_0$ antiferromagnetic ground state near $y = 0$ to austenitic ferromagnetic $L2_1$ Heusler phase near $y = 1$ due to doping of In impurity for Mn. The off stoichiometric alloys prepared by rapid quenching are structurally metastable and dissociate into a mixture of $L2_1$ (Ni$_2$MnIn) and $L1_0$ (NiMn) phases upon temper annealing. Despite this structural disintegration, the martensitic transformation temperature remains invariant in the temper annealed alloys. Investigations of the local structure of the constituent atoms reveal the presence of strongly coupled Ni$_2$MnIn and NiMn structural units in the temper annealed as well as the rapidly quenched off stoichiometric Ni$_2$Mn$_{2-y}$In$_y$ alloys irrespective of their crystal structure. This random packing of the $L2_1$ and $L1_0$ structural units seems to be responsible for invariance of martensitic transition temperature in the temper annealed alloys as well as the absence of strain glass transition in rapidly quenched alloys.",2107.11551v1 2006-03-24,Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films,"We investigate the structure and magneto-transport properties of thin films of the Co_2Cr_xFe_(1-x)Al full-Heusler compound, which is predicted to be a half-metal by first-principles theoretical calculations. Thin films are deposited by magnetron sputtering at room temperature on various substrates in order to tune the growth from polycrystalline on thermally oxidized Si substrates to highly textured and even epitaxial on MgO(001) substrates, respectively. Our Heusler films are magnetically very soft and ferromagnetic with Curie temperatures up to 630 K. The total magnetic moment is reduced compared to the theoretical bulk value, but still comparable to values reported for films grown at elevated temperature. Polycrystalline Heusler films combined with MgO barriers are incorporated into magnetic tunnel junctions and yield 37% magnetoresistance at room temperature.",0603649v1 2013-01-31,A New Spin Gapless Semiconductors Family: Quaternary Heusler Compounds,"Using first-principles calculations, we investigate the band structures of a series of quaternary LiMgPdSn-type Heusler compounds. Our calculation results show that five compounds CoFeMnSi, CoFeCrAl, CoMnCrSi, CoFeVSi and FeMnCrSb possess unique electronic structures characterized by a half-metallic gap in one spin direction while a zero-width gap in the other spin direction showing spin gapless semiconducting behavior. We further analysis the electronic and magnetic properties of all quaternary Heusler alloys involved, and reveal a semi-empirical general rule (total valence electrons number being 26 or 28) for indentifying spin gapless semiconductors in Heusler compounds. The influences of lattice distortion and main-group element change have also been discussed.",1301.7488v1 2016-03-17,Ultrafast Local Magnetization and Demagnetization in Heusler Alloys,"With the goal of pushing Spintronic devices towards faster and faster timescales, we demonstrate, using ab-intio time-dependent density functional theory simulations of bulk Heusler compounds subject to ultrashort intense laser pulses, that the local magnetic moment can increase or decrease in a few femtoseconds. This speed is due to the all optical nature of the process, which transfers spin moment from one sublattice to another. This transfer depends on easily tunable laser parameters. By comparing the spin dynamics of a variety of Heusler (or half-Heusler) compounds, we demonstrate that the density of states explains the observed moment transfer; most the physics of inter sublattice moment transfer is due to the flow of spin current which is governed by availability of states above the Fermi level.",1603.05603v1 2009-10-26,Direct determination of the surface termination in full Heusler alloys by means of low energy electron diffraction,"The performance of Heusler based magnetoresistive multilayer devices depends crucially on the spin polarization and thus on the structural details of the involved surfaces. Using low energy electron diffraction (LEED), one can non-destructively distinguish between important surface terminations of Co2XY full-Heusler alloys. We present an analysis of the LEED patterns of the Y-Z ,the vacancy-Z, the Co and the disordered B2 and A2 terminations. As an example, we show that the surface geometries of bulk L21 ordered Co2MnSi and bulk B2 disordered Co2Cr0.6Fe0.4Al can be determined by comparing the experimental LEED patterns with the presented reference patterns.",0910.4909v2 2013-04-09,Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi,"In this paper, we investigate the half-metallicity of Heusler alloys Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance measurements. It is found that, with the increase of Cr content x, the Fermi level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of conduction band, and a large half-metallic band gap of 0.75 eV is obtained for x=0.75. We then successfully synthesized a series Heusler Fe2Co1-xCrxSi polycrystalline ribbon samples. The results of X-ray diffraction indicate that the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order and the saturation magnetic moment follows half-metallic Slater-Pauling rule. Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, 0.75) show a negative value suggesting they are stable half-metallic ferromagnets.",1304.2602v1 2014-02-18,Interplay of growth mode and thermally induced spin accumulation in epitaxial Al/Co$_2$TiSi/Al and Al/Co$_2$TiGe/Al contacts,"The feasibility of thermally driven spin injectors built from half-metallic Heusler alloys inserted between aluminum leads was investigated by means of {\em ab initio} calculations of the thermodynamic equilibrium and electronic transport. We have focused on two main issues and found that: (i) the interface between Al and the closely lattice-matched Heusler alloys of type Co$_2$Ti$Z$ ($Z=$ Si or Ge) is stable under various growth conditions; and (ii) the conventional and spin-dependent Seebeck coefficients in such heterojunctions exhibit a strong dependence on both the spacer and the atomic composition of the Al/Heusler interface. The latter quantity gives a measure of the spin accumulation and varies between $+8$~$\mu$V/K and $-3$~$\mu$V/K near $300$~K, depending on whether a Ti-Ge or a Co-Co plane makes the contact between Al and Co$_2$TiGe in the trilayer. Our results show that it is in principle possible to tailor the spin-caloric effects by a targeted growth control of the samples.",1402.4396v2 2016-04-19,Half Heusler Alloys for Efficient Thermoelectric Power Conversion,"Half-Heusler (HH) phases (space group F43m, Clb) are increasingly gaining attention as promising thermoelectric materials in view of their thermal stability, scalability, and environmental benignity as well as efficient power output. Until recently, the verifiable dimensionless figure of merit (ZT) of HH phases has remained moderate near 1, which limits the power conversion efficiency of these materials. We report herein ZT~1.3 in n-type (Hf,Zr)NiSn alloys near 850 K developed through elemental substitution and simultaneously embedment of nanoparticles in the HH matrix, obtained by annealing the samples close to their melting temperatures. Introduction of mass fluctuation and scattering centers play a key role in the high ZT measured, as shown by the reduction of thermal conductivity and increase of thermopower. Based on computation, the power conversion efficiency of a n-p couple module based on the new n-type (Hf,Zr,Ti)NiSn particles-in-matrix composite and recently reported high-ZT p-type HH phases is expected to reach 13%, comparable to that of state-of-the-art materials, but with the mentioned additional materials and environmental attributes. Since the high efficiency is obtained without tuning the microstructure of the Half-Heusler phases, it leaves room for further optimization.",1604.05397v2 2016-12-29,Magnetovolume Effects in Heusler Compounds via First-Principles Calculations,"Heusler alloys are promising for several applications, including magnetic refrigeration, due to high magnetocaloric and magnetovolume effects. One way to optimize this potential is by increasing the magnetovolume effect. Using density functional theory with the Korringa-Kohn-Rostoker method, we calculate the effective exchange interaction energies and corresponding mean field Curie temperature as a function of the volume (hydrostatic pressure) in several L2 1 -type Co 2 YZ Heusler alloys. Different qualitative trends and signs of the pressure derivatives of the Curie temperature and moments are found among these compounds, discussed and compared with previous calculations and experiments.",1612.09133v1 2020-03-20,A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculations,"In the present work, the aspects of magnetic and structural properties of Ni-Mn-Ga alloys are described in the framework of fist-principles approach and mapped into ternary composition diagrams. The stable atomic arrangement and magnetic alignment for compositions with cubic austenite and tetragonal martensite structures across phase diagrams are predicted. It is shown that Ni- and Ga-rich compositions possess the regular Heusler structure in contrast to Mn-rich compositions with inverse Heusler structure as favorable one. Compositions with unstable austenite structure are concentrated in the left and right sides of diagram whereas compositions with unstable martensite structure are located in the low-middle part of diagram. The magnetic phase diagrams showing regions with the ferromagnetic order and the complex ferrimagnetic order for austenitic and martensitic compositions are obtained. The results of calculations are in a good agreement with available experimental data.",2003.09128v1 2020-09-24,Electronic Structure and Thermoelectric Properties of Half-Heusler Alloys NiTZ,"We have investigated the electronic and thermoelectric properties of half-Heusler alloys NiTZ (T = Sc, and Ti; Z = P, As, Sn, and Sb) having 18 valence electron. Calculations are performed by means of density functional theory and Boltzmann transport equation with constant relaxation time approximation, validated by NiTiSn. The chosen half-Heuslers are found to be an indirect band gap semiconductor, and the lattice thermal conductivity is comparable with the state-of-the-art thermoelectric materials. The estimated power factor for NiScP, NiScAs, and NiScSb reveals that their thermoelectric performance can be enhanced by appropriate doping rate. The value of ZT found for NiScP, NiScAs, and NiScSb are 0.46, 0.35, and 0.29, respectively at 1200 K.",2009.11916v4 2021-05-11,First-principles calculations and experimental studies on Co2FeGe Heusler alloy nanoparticles for spintronics applications,"Here, we report the synthesis and physical properties of Co2FeGe (CFG) Heusler alloy (HA) nanoparticles (NPs). The NPs of size 23 nm are prepared using the co-precipitation method. X-ray and selected area electron diffraction patterns have confirmed the cubic Heusler phase of the NPs with the A2-disorder. These NPs are soft ferromagnetic, and exhibit a high saturation magnetization (Ms) along with a very high Curie temperature (Tc) of 1060 K. The observed Tc value matches closely with the theoretically calculated one following a model provided by Wurmehl et al. [1]. The high Ms and Tc make the present system a potential candidate for magnetically activated nano-devices working at high temperatures. The near-integral value 5.9 mehoB/f.u. of Ms at low temperatures indicates that the half-metallic ferromagnetism is preserved even in the particles even on the 20 nm length scale. Additionally, we have facilitated the existing HA-NP preparation method, which can be used in synthesizing other HA-NPs. The first-principles density functional theory computations complement the experimental results.",2105.05200v1 2021-09-24,Impact of local arrangement of Fe and Ni on the phase stability and magnetocrystalline anisotropy in Fe-Ni-Al Heusler alloys,"On the basis of density functional calculations, we report on a comprehensive study of the influences of atomic arrangement and Ni substitution for Al on the ground state structural and magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss systematically the competition between five Heusler-type structures formed by shuffles of Fe and Ni atoms and their thermodynamic stability. All~Ni-rich Fe$_2$Ni$_{1+x}$Al$_{1-x}$ tend to decompose into a dual-phase mixture consisting of Fe$_2$NiAl and~FeNi. The~successive replacement of Ni by Al leads to a change of ground state structure and eventually an increase in magnetocrystalline anisotropy energy~(MAE). We predict for stoichiometric Fe$_2$NiAl a ground state structure with nearly cubic lattice parameters but alternating layers of Fe and Ni possessing an uniaxial MAE which is even larger than tetragonal L1$_0$-FeNi. This opens an alternative route for improving the phase stability and magnetic properties in FeNi-based permanent magnets.",2109.12005v2 2022-08-31,Unusual kinetic properties of usual Heusler alloys,"The review considers various groups of Heusler compounds, which can have the properties of a semiconductor, a half-metallic ferromagnet, a spin gapless semiconductor, a topological semimetal, and a noncollinear antiferromagnet. In these Heusler compounds, ""conventional"" from the point of view of the crystal structure, unusual kinetic and magnetic properties can be observed, which are caused by the features of their electronic structure (e.g., presence of an energy gap for one spin projection) and magnetic state (e.g., strong ferromagnetism, compensated ferrimagnetism, etc.). Their magnetic and kinetic characteristics are very sensitive to external influences. Depending on the alloy composition and external parameters, transitions between the considered states can be realized. All this opens up further prospects for controlling the electronic and magnetic characteristics of such compounds and their practical application.",2208.14868v1 2024-03-13,Study of Physical Characteristics of the New Half-Heusler Alloy BaHgSn by DFT Analysis,"To investigate the physical characteristics of the half-Heusler BaHgSn molecule, we used theoretical calculations within the Density Functional Theory (DFT) framework utilizing the LSDA+mBJ technique in this study. Using the optimal lattice parameters, we discover that half-Heusler BaHgSn exhibits a Dirac semimetal behavior with a band gap of 0.1 eV. Thomas Charpin's numerical first-principles calculation approach was applied to determine the elastic constants of hexagonal BaHgSn alloys. The material's optical characteristics verified its prospective use in infrared-visible devices. According to a thermo-electric properties analysis, at 20x10^18 {\Omega}-1.m-1.s-1, the electrical conductivity reaches its maximum after increasing gradually up to 500 K. Compared to other compounds, these results indicate that BaHgSn has potential for use in opto-electronic and thermo-electric devices.",2403.08483v1 2019-11-12,"Formation and magnetic properties of spark plasma sintered Mn$_{3-δ}$ ($δ$ = 0, 1) alloys","We present the synthesis of D0$_{22}$ Mn$_{3 - \delta}$Ga ($\delta$ = 0, 1) Heusler alloys by Spark Plasma Sintering method. The single phase Mn$_3$Ga (T$_\mathrm{c}$ $\simeq$ 780 K) is synthesized, while Mn$_2$Ga (T$_\mathrm{c}$ $\simeq$ 710 K) is found to coexist with a near-stoichiometric room temperature paramagnetic Mn$_9$Ga$_5$~($\approx$ 15 \%) phase due to its lower formation energy, as confirmed from our density functional theory (DFT) calculations. The alloys show hard magnetic behavior with large room temperature spontaneous magnetization m$_s$(80 kOe) = 1.63 (0.83) $\mu_\mathrm{B}$/f.u. and coercivity H$_\mathrm{c}$ = 4.28 (3.35) kOe for Mn$_3$Ga (Mn$_2$Ga). The magnetic properties are further investigated till T$_\mathrm{c}$ and the H$_\mathrm{c}$ (T) analysis by Stoner-Wohlfarth model shows the nucleation mechanism for the magnetization reversal. The experimental results are well supported by DFT calculations, which reveal that the ground state of D0$_{22}$ Mn$_2$Ga is achieved by the removal of Mn-atoms from full Heusler Mn$_3$Ga structure in accordance with half Heusler alloy picture.",1911.05040v1 1999-10-15,"Electronic structure and magnetism of Fe$_{3-x}$V$_{x}$X (X = Si, Ga and Al) alloys by the KKR-CPA method","We present first principles charge- and spin-selfconsistent electronic structure computations on the Heusler-type disordered alloys Fe$_{3-x}$V$_{x}$X for three different metalloids X=(Si, Ga and Al). In these calculations we use the methodology based on the Korringa-Kohn- Rostoker formalism and the coherent-potential approximation (KKR-CPA), generalized to treat disorder in multi-component complex alloys.",9910249v1 2003-09-11,An efficient control of Curie temperature $T_C$ in Ni-Mn-Ga alloys,"We have studied the influence of alloying with a fourth element on the temperature of ferromagnetic ordering $T_C$ in Ni-Mn-Ga Heusler alloys. It is found that $T_C$ increases or decreases, depending on the substitution. The increase of $T_C$ is observed when Ni is substituted by either Fe or Co. On the contrary, the substitution of Mn for V or Ga for In strongly reduces $T_C$.",0309271v1 2020-04-25,Mechanical and thermodynamical properties of $β-Cu-Al-Mn$ alloys along the $Cu_3Al \to Cu_2AlMn$ compositional line,"The elastic properties of $Cu-Al-Mn$ alloys with compositions along the $Cu_3Al \to Cu_2AlMn$ line and $bcc$-based structures, are studied by means of first-principles calculations. From the calculated elastic constants, the Zener's anisotropy, sound velocities and Debye temperature are determined. The theoretical results compare well with the available experimental data. The influence of vibrations is introduced through the quasi-harmonic Debye model, and different properties are studied as functions of temperature and composition.",2004.12253v1 2004-07-01,Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al,"The Heusler alloy is used as an electrode of magnetic tunneling junctions. The junctions are deposited by magnetron dc sputtering using shadow mask techniques with AlO_{x} as a barrier and cobalt as counter electrode. Measurements of the magnetoresistive differential conductivity in a temperature range between 4K and 300K are shown. An analysis of the barrier properties applying the Simmons model to the bias dependent junction conductivity is performed. VSM measurements were carried out to examine the magnetic properties of the samples.",0407034v1 2011-02-18,Perpendicular magnetic anisotropy of full-Heusler films in Pt/Co2FeAl/MgO trilayers,"We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is thermally stable that the anisotropy energy density Ku is 1.3{\times}106 erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 oC. The thicknesses of Co2FeAl and MgO layers greatly affect the PMA. Our results provide an effective way to realize relative thick perpendicularly magnetized Heusler alloy films.",1102.3802v1 2013-09-25,Prediction of half metallic properties in Ti\raisebox{-.2ex}{\scriptsize 2}CoSi Heusler alloy based on density functional theory,"The electronic and magnetic properties of Ti\raisebox{-.2ex}{\scriptsize 2}CoSi Heusler compound are investigated using density functional calculations. The optimized lattice constant is found to be 6.030 A. The compound is a half-metallic ferromagnet with an energy gap in minority spin channel of 0.652 eV at equilibrium lattice constant, which leads to a 100% spin-polarization. The obtained total magnetic moment from spin-polarized calculations is 3.0 $\mu_{B}$ for values of lattice constants higher than 5.941 A. The half-metallicity is spoiled for a compressed volume of 4%, suggesting a possible application as pressure sensitive material.",1309.6427v1 2013-12-20,Multiple phases in sputtered Cr2CoGa films,"By magnetron co-sputtering, thin films of a nominal Cr2CoGa compound were deposited on MgO and MgAl2O4. To achieve crystallisation in the inverse Heusler structure, different heat treatments were tested. Instead of the inverse Heusler structure, we observed phase separation and precipitate formation in dependence on the heat treatment. The main precipitate is Cr3Ga in A15 structure. The remainder forms Co-rich CoGa in the B2 structure and possibly Cr-rich CoCr in the sigma-phase.",1312.6014v2 2022-01-14,Antisite disorder and phase segregation in Mn$_{2}$NiSn,"A systematic study of crystal structure, local structure, magnetic and transport properties in quenched and temper annealed Ni$_{2-x}$Mn$_{1+x}$Sn alloys indicate the formation of Mn$_3$Sn type structural defects caused by an antisite disorder between Mn and Sn occupying the Y and Z sublattices of X$_2$YZ Heusler structure. The antisite disorder is caused by the substitution of Ni by Mn at the X sites. On temper annealing, these defects segregate and phase separate into $L2_1$ Heusler and $D0_{19}$ Mn$_3$Sn type phases.",2201.05283v1 2016-03-30,Probing the possibility of coexistence of martensite transition and half-metallicity in Ni and Co-based full Heusler Alloys : An ab initio Calculation,"Using first-principles calculations based on density functional theory, we have studied the mechanical, electronic, and magnetic properties of Heusler alloys, namely, Ni$_{2}BC$ and Co$_{2}BC$ ($B$ = Sc, Ti, V, Cr and Mn as well as Y, Zr, Nb, Mo and Tc; $C$ = Ga and Sn). On the basis of electronic structure (density of states) and mechanical properties (tetragonal shear constant), as well as magnetic interactions (Heisenberg exchange coupling parameters), we probe the properties of these materials in detail. We calculate the formation energy of these alloys in the (face-centered) cubic austenite structure to probe the stability of all these materials. From the energetic point of view, we have studied the possibility of the electronically stable alloys having a tetragonal phase lower in energy compared to the respective cubic phase. A large number of the magnetic alloys is found to have the cubic phase as their ground state. On the other hand, for another class of alloys, the tetragonal phase has been found to have lower energy compared to the cubic phase. Further, we find that the values of tetragonal shear constant show a consistent trend : a high positive value for materials not prone to tetragonal transition and low or negative for others. In the literature, materials, which have been seen to undergo the martensite transition, are found to be metallic in nature. We probe here if there is any Heusler alloy which has a tendency to undergo a tetragonal transition and at the same time possesses a high spin polarization at the Fermi level. From our study, it is found that out of the four materials, which exhibit a martensite phase as their ground state, three of these, namely, Ni$_{2}$MnGa, Ni$_{2}$MoGa and Co$_{2}$NbSn have a metallic nature; on the contrary, Co$_{2}$MoGa exhibits a high spin polarization.",1603.09112v1 2008-04-23,Hybridization Effects in Ni-Mn based Shape Memory Alloys: XAFS Study,"Martensitic and magnetic properties of ferromagnetic shape memory alloys are known to depend up on structural modulations and associated changes in the Fermi surface. These modulations although periodic and spanning over multiple unit cells, involve movement of atoms typically of the order of 0.01A. Therefore X-ray Absorption Fine Structure (XAFS) is an ideal tool to map both, local atomic movements and changes in density of states (DOS) due to changing hybridization as the system transforms from austenitic to martensitic phase. This paper presents a compilation of our XAFS studies on the Ni-Mn based shape memory alloys. A complete description of the changes in local structure around the constituent metal ions in the following alloy compositions: Ni2+xMn1-xGa, Ni2Mn1.4Sn0.6 and Ni2Mn1.4In0.6 in the austenitic and martensitic phases have been obtained. The results give the new experimental evidence for the crucial hybridization component that influences and leads to structural transition in these Ni-Mn based Heusler alloys.",0804.3663v1 2018-12-03,"Mn2V0.5Co0.5Z (Z= Ga, Al) Heusler alloys: Fully compensated ferrimagnets with high Tc and compensation temperature","High TC fully compensated ferrimagnets are potential candidates for spin transfer torque based spintronic devices. We report the structural and magnetic properties of high TC fully compensated ferrimagnets Mn2V0.5Co0.5Z where Z is Ga, Al, in the melt spun ribbon and arc melted bulk form. While the parent alloys Mn2YZ where Y is V, Co and Z is Ga, Al exhibits a magnetic moment value around 2 muB per f.u, the Mn2V0.5Co0.5Ga alloy exhibits room temperature nearly fully compensated moment value of 0.09 and 0.13 muB per f.u. in the bulk and ribbon form respectively. For Mn2V0.5Co0.5Al this turned out to be 0.04 and 0.08 muB per f.u. In Contrast to the bulk sample's Neel P type ferrimagnetic behaviour, ribbon samples exhibit Neel N type ferrimagnetic characteristic with a high compensation temperature of 420 K for Ga alloy and 275 K for Al alloy. The observed TC values are more than 640 K for all samples. The differences in the magnetic properties of arc melted and melt spun alloys indicates that even a slight variation in stoichiometry and sample preparation method can influence the physical properties of a compensated system.",1812.00714v1 2021-11-12,"First-principles investigations of the electronic, magnetic and thermoelectric properties of VTiRhZ (Z= Al, Ga, In) Quaternary Heusler Alloys","Calculations using density functional theory (DFT) were performed to investigate the structural, dynamical, mechanical, electronic, magnetic, and thermoelectric properties of VTiRhZ (Z = Al, Ga, In) alloys. The most stable structure of these alloys was found to be the type-I configuration. Using GGA-PBE functional, VTiRhGa, and VTiRhIn alloys are predicted as half-metallic ferromagnets with a 100% spin-polarization and a total magnetic moment of 3{\mu}B, which is promising for spintronic applications. The thermoelectric properties and lattice thermal conductivity of VTiRhZ alloys were obtained using the Boltzmann transport theory within the constant relaxation time and Slack equation, respectively. The figure-of-merit (ZT) values of VTiRhAl, VTiRhGa, and VTiRhIn alloys were found to be 0.96, 0.88 and 0.64, respectively, which are promising for future thermoelectric applications.",2111.06915v1 2022-10-24,Ab-initio calculation of the Hubbard $U$ and Hund exchange $J$ in local moment magnets: The case of Mn-based full Heusler compounds,"Mn-based full Heusler compounds possess well-defined local atomic Mn moments, and thus the correlation effects between localized d electrons are expected to play an important role in determining the electronic and magnetic properties of these materials. Employing ab-initio calculations in conjunction with the constrained random-phase approximation (cRPA) method, we calculate the strength of the effective on-site Coulomb interaction parameters (Hubbard U and Hund exchange J) in the case of X2MnZ full Heusler compounds with X being one of Ni, Pd or Cu, and Z being one of In, Sn, Sb or Te. We show that the Z element (or sp element) in Heusler compounds significantly reduces the strength of the Hubbard U parameter for Mn 3d electrons compared to the elementary bulk Mn. On the contrary, the effect of the sp-atom on the strength of the U parameter of Ni, Cu or Pd valence d electrons is not so substantial with respect to the elementary bulk values. The U values for all transition metal atoms decrease with increasing sp electron number in the In-Sn-Sb-Te sequence. Our cRPA calculations reveal that despite their well-defined local magnetic moments, the Mn-based full Heusler alloys fall into the category of the weakly correlated materials.",2210.13061v1 2023-03-04,Giant anomalous Hall and Nernst conductivities in magnetic all-$d$ metal Heusler alloys,"All-$d$ Heuslers are a category of novel compounds combining versatile functionalities such as caloric responses and spintronics with enhanced mechanical properties. Despite the promising transport properties (anomalous Hall (AHC) and anomalous Nernst (ANC) conductivities) shown in the conventional Co$_2$XY Heuslers with $p$-$d$ hybridization, the all-$d$ Heuslers with only $d$-$d$ hybridization open a new horizon to search for new candidates with outstanding transport properties. In this work, we evaluate the AHC and ANC for thermodynamically stable ferro/ferri-magnetic all-$d$-metal regular Heusler compounds based on high-throughput first-principles calculations. It is observed that quite a few materials exhibit giant AHCs and ANCs, such as cubic Re$_2$TaMn with an AHC of 2011 S/cm, and tetragonal Pt$_2$CrRh with an AHC of 1966 S/cm and an ANC of 7.50 A/mK. Comprehensive analysis on the electronic structure reveals that the high AHC can be attributed to the occurrence of the Weyl nodes or gapped nodal lines in the neighbourhood of the Fermi level. The correlations between such transport properties and the number of valence electrons are also thoroughly investigated, which provides a practical guidance to tailor AHC and ANC via chemical doping for transverse thermoelectric applications.",2303.02351v1 2005-12-15,"Search for half-metallic ferrimagnetism in V-based Heusler alloys Mn$_2$VZ (Z$=$Al, Ga, In, Si, Ge, Sn)","Using a state-of-the-art full-potential electronic structure method within the local spin density approximation, we study the electronic and magnetic structure of Mn$_2$V-based full Heusler alloys: Mn$_2$VZ (Z=Al, Ga, In, Si, Ge, and Sn). We show that small expansion of the calculated theoretical equilibrium lattice constants restores the half-metallic ferrimagnetism in these compounds. Moreover a small degree of disorder between the V and Z atoms, although iduces some states within the gap, it preserves the Slater-Pauling behaviour of the spin magnetic moments and the alloys keep a high degree of spin-polarisation at the Fermi level opening the way for a half-metallic compensated ferrimagnet.",0512361v1 2006-01-24,Lattice dynamics and phonon softening in Ni-Mn-Al Heusler alloys,"Inelastic and elastic neutron scattering have been used to study a single crystal of the Ni$_{54}$Mn$_{23}$Al$_{23}$ Heusler alloy over a broad temperature range. The paper reports the first experimental determination of the low-lying phonon dispersion curves for this alloy system. We find that the frequencies of the TA$_2$ modes are relatively low. This branch exhibits an anomaly (dip) at a wave number $\xi_{0} ={1/3}\approx 0.33$, which softens with decreasing temperature. Associated with this anomalous dip at $\xi_{0}$, an elastic central peak scattering is also present. We have also observed satellites due to the magnetic ordering.",0601546v1 2006-06-02,Temperature and magnetic field dependences of the elastic constants of Ni-Mn-Al magnetic Heusler alloys,"We report on measurements of the adiabatic second order elastic constants of the off-stoichiometric Ni$_{54}$Mn$_{23}$Al$_{23}$ single crystalline Heusler alloy. The variation in the temperature dependence of the elastic constants has been investigated across the magnetic transition and over a broad temperature range. Anomalies in the temperature behaviour of the elastic constants have been found in the vicinity of the magnetic phase transition. Measurements under applied magnetic field, both isothermal and variable temperature, show that the value of the elastic constants depends on magnetic order, thus giving evidence for magnetoelastic coupling in this alloy system.",0606065v1 2006-06-28,The study of electronic and magnetic properties of the partially disordered pseudo-Heusler alloy Co2Fe0.4Cr0.6Al : an augmented space approach,"In this communication we present a study of the electronic structure of partially disordered bulk and (100) thin film of quaternary pseudo-Heusler alloy Co$_2$Fe$_{0.4}$Cr$_{0.6}$Al in the L2$_1$ phase using the Augmented Space recursion (ASR) in a scalar-relativistic tight binding linear muffin-tin orbitals (TB-LMTO) basis. We study the orbital resolved magnetic moment contributions of the constituents of the alloy. Our theoretical predictions match well with the available experimental observations for the magnetic moments of Fe and Co but they overestimate that of Cr. For a (100) thin film, layer as well as orbital resolved properties have been studied.",0606737v2 2009-04-17,Ferromagnetism and Electronic Structures of Nonstoichiometric Heusler-Alloy Fe_3-xMn_xSi Epilayers Grown on Ge(111),"For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloys Fe_3-xMn_xSi epitaxially grown on Ge(111) by tuning the Mn composition x. Interestingly, we obtain L2_1-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with x ~ 0.6 exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric Fe_3-xMn_xSi alloys become half-metallic for 0.75 < x < 1.5. We discuss the possibility of room-temperature ferromagnetic Fe_3-xMn_xSi/Ge epilayers with high spin polarization.",0904.2610v1 2010-08-24,"Magnetism of mixed quaternary Heusler alloys: (Ni,T)$_{2}$MnSn (T=Cu,Pd) as a case study","The electronic properties, exchange interactions, finite-temperature magnetism, and transport properties of random quaternary Heusler Ni$_{2}$MnSn alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it ab initio} calculations over the entire range of dopant concentrations. While the magnetic moments are only weakly dependent on the alloy composition, the Curie temperatures exhibit strongly non-linear behavior with respect to Cu-doping in contrast with an almost linear concentration dependence in the case of Pd-doping. The present parameter-free theory agrees qualitatively and also reasonably well quantitatively with the available experimental results. An analysis of exchange interactions is provided for a deeper understanding of the problem. The dopant atoms perturb electronic structure close to the Fermi energy only weakly and the residual resistivity thus obeys a simple Nordheim rule. The dominating contribution to the temperature-dependent resistivity is due to thermodynamical fluctuations originating from the spin-disorder, which, according to our calculations, can be described successfully via the disordered local moments model. Results based on this model agree fairly well with the measured values of spin-disorder induced resistivity.",1008.4060v1 2012-08-10,"Electronic structure, optical and magnetic properties of Co$_{2}$FeGe Heusler alloy films","Optical properties of ferromagnetic half-metallic full-Heusler Co$_{2}$FeGe alloy are investigated experimentally and theoretically. Co$_{2}$FeGe thin films were obtained by DC magnetron sputtering and show the saturation magnetization at $T$=10 K of $m\approx$5.6 $\mu_{B}$/f.u., close to the value predicted by the Slater-Pauling rule. First-principles calculations of the electronic structure and the dielectric tensor are performed using the full-potential linearized-augmented-plane-wave method in the generalized gradient (GGA) and GGA+U approximations. The measured interband optical conductivity spectrum for the alloy exhibits a strong absorption band in the 1 - 4 eV energy range with pronounced fine structure, which agrees well with the calculated half-metallic spectrum of the system, suggesting a near perfect spin-polarization in the material.",1208.2193v1 2013-01-31,"Structure and magnetic properties of Heusler alloy Fe2NiZ (Z=Al, Ga, Si and Ge)","The Heusler alloys Fe2NiZ (Z=Al, Ga, Si and Ge) have been synthesized and investigated focusing on the phase stability and the magnetic properties. The experimental and theoretical results reveal the covalent bonding originated from p-d hybridization takes an important role in these alloys, which dominates the stability of ordered structure but leads to the decline of the band splitting. The electronic structure shows the IV group main group element (Si and Ge) provides stronger covalent effect than that of the III group element (Al and Ga). It has been found that the variations of the physical parameters, lattice constants, critical ordering temperature, magnetic moments and Curie temperature, precisely follow these covalent characters.",1301.7489v1 2013-04-20,Antiferromagnetic Exchange Interactions in Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ ferromagnetic Heusler alloy,"Magnetism in Ni-Mn-Z (Z = Ga,In,Sn,Sb) Heusler alloys has so far been predominantly attributed to Rudermann-Kittel-Kasuya-Yoshida type interactions between Mn atoms. We investigate magnetic interactions in one such alloy, Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and attempt to explain the origin of antiferromagnetic (AFM) interactions that coexist with ferromagnetic ones. Through the combination of x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD), we find that Ni plays an important role along with Mn in the overall magnetism. A significant hybridization that develops between Mn and Ni orbitals results in a small antiferromagnetic moment at Ni sites. The shift in the XMCD hysteresis loops in the martensitic phase suggests that antiferromagnetism results from superexchange like interactions between Mn atoms mediated by Ni.",1304.5580v1 2014-05-26,Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa,"Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300~fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320~fs, which is comparable to the quenching of the structural modulation.",1405.6534v1 2014-08-11,High spin polarization in CoFeMnGe quaternary Heusler alloy,"We report the structure, magnetic property and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to exist in the L21 structure with considerable amount of DO3 disorder. Thermal analysis result indicated the Curie temperature is about 711K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 {plus/minus}0.1 was deduced using point contact Andreev reflection (PCAR) measurements. Half-metallic trend in the resistivity has also been observed in the temperature range of 5 K to 300 K. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.",1408.2408v2 2015-01-19,Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$,"We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$ by direct measurements in pulsed magnetic fields up to 6 and 20 T. The results in 6 T are compared with data obtained from heat-capacity experiments. We find a saturation of the inverse MCE, related to the first-order martensitic transition, with a maximum adiabatic temperature change of $\Delta T_{ad} = -7$ K at 250 K and a conventional field-dependent MCE near the second-order ferromagnetic transition in the austenitic phase. The pulsed magnetic field data allow for an analysis of the temperature response of the sample to the magnetic field on a time scale of $\sim 10$ to 100 ms which is on the order of typical operation frequencies (10 to 100 Hz) of magnetocaloric cooling devices. Our results disclose that in shape-memory alloys the different contributions to the MCE and hysteresis effects around the martensitic transition have to be carefully considered for future cooling applications.",1501.04430v1 2015-04-14,Effect of ball milling and post annealing on structural and magnetic properties in Ni50Mn36Fe2Sb12 Heusler alloy,"The effect of ball milling on the structural, magnetic and exchange bias properties of Ni50Mn36Fe2Sb12 Heusler alloys was studied. The ball milled samples exhibited coexisting austenite and martensite phases at room temperature, while annealing supresses the austenite phase completely. Ball milling was found to reduce the grain size, which resulted in the weakening of the ferromagnetic properties. An exchange bias field of 111 Oe and coercivity of 826 Oe were observed at 5 K in the as-milled sample, in contrast to the bulk alloy values of 288 Oe and 292 Oe, respectively. Annealing causes an increase in the ferromagnetic ordering and a decrease in the interfacial exchange coupling, resulting in a decrease of both exchange bias and coercivity.",1504.03460v1 2015-06-23,Spin polarization studies in half-metallic Co2TiX (X = Ge and Sn) Heusler alloys,"In this paper, we investigated the Co2TiX (X = Ge, Sn) Heusler alloys by structural, magnetic and spin polarization measurements to probe the half-metallic nature. Alloys are synthesized using the arc melting technique, and found to exist in L21 crystal structure with Fm-3m space group. Curie temperature (TC) is found to be 384 and 371 K for Co2TiGe and Co2TiSn respectively. The saturation magnetization (MS) value of 1.8 and 2.0 Bohr magneton/f.u. are obtained at 5 K for for Co2TiGe and Co2TiSn respectively, compared to 2.0 Bohr magneton/f.u. calculated by Slater-Pauling rule. To obtain the spin polarization value, differential conductance curves are recorded at the ferromagnetic/superconducting point contact at 4.2 K. The current spin polarization (P) value of 0.63 and 0.64 are deduced for Co2TiGe and Co2TiSn respectively. Considering the high current spin polarization and TC, these materials appear to be promising for spintronic devices.",1506.07109v1 2015-09-20,"Electronic structure, magnetism and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys","We present a combined theoretical and experimental study of two quaternary Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for spintronics applications. Magnetization measurement shows the saturation magnetization and transition temperature to be $3\; \mu_B$, $866$ K and $0.9 \; \mu_B$, $358$ K for CFCG and CMCA respectively. The magnetization values agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. A striking difference between the two systems is their structure; CFCG crystallizes in fully ordered Y-type structure while CMCA has L2$_1$ disordered structure. The antisite disorder adds a somewhat unique property to the second compound, which arises due to the probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is possibly expected due to comparable electronegativities of Al and Cr/Mn. {\it Ab-initio} simulation predicted a unique transition from half metallic ferromagnet to metallic antiferromagnet beyond a critical excess amount of Al in the alloy.",1509.05971v2 2016-08-22,Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys,"The all-d-metal Mn2-based Heusler ferromagnetic shape memory alloys Mn50Ni40-xCoxTi10 (x = 8 and 9.5) are realized. With a generic comparison between d-metal Ti and main-group elements in lowering the transformation temperature, the magnetostructural martensitic transformations are established by further introducing Co to produce local ferromagnetic Mn-Co-Mn configurations. A 5-fold modulation and (3, -2) stacking of [00 10] of martensite are determined by XRD and HRTEM analysis. Based on the transformation, a large magneto-strain of 6900 ppm and a large volume change of -2.54% are observed in polycrystalline samples, which makes the all-d-metal magnetic martensitic alloys of interest for magnetic/pressure multi-field driven applications.",1608.06301v1 2017-08-28,"Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond","We present our recent results on temperature behaviour of magnetization observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished in the M-T diagram: (I) low temperature martensitic phase (with the Curie temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM and T_MS) and (III) high temperature austenitic phase (with the Curie temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS and T_CA). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M-T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg-Landau scenario.",1708.08368v1 2018-06-04,"Atomistic Study of the Electronic Contact Resistivity Between the Half-Heusler Alloys (HfCoSb, HfZrCoSb, HfZrNiSn) and the Metal Ag","Half-Heusler(HH) alloys have shown promising thermoelectric properties in the medium and high temperature range. To harness these material properties for thermoelectric applications, it is important to realize electrical contacts with low electrical contact resistivity. However, little is known about the detailed structural and electronic properties of such contacts, and the expected values of contact resistivity. Here, we employ atomistic ab initio calculations to study electrical contacts in a subclass of HH alloys consisting of the compounds HfCoSb, HfZrCoSb, and HfZrNiSn. By using Ag as a prototypical metal, we show that the termination of the HH material critically determines the presence or absence of strong deformations at the interface. Our study includes contacts to doped materials, and the results indicate that the p-type materials generally form ohmic contacts while the n-type materials have a small Schottky barrier. We calculate the temperature dependence of the contact resistivity in the low to medium temperature range and provide quantitative values that set lower limits for these systems.",1806.01375v1 2020-01-03,Neutron diffraction and ab initio studies on the fully compensated ferrimagnetic characteristics of Mn2V1-xCoxGa Heusler alloys,"Neutron diffraction and ab initio studies were carried out on Mn2V1-xCoxGa (x=0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high TC fully compensated ferrimagnetic characteristic for x=0.5. A combined analysis of neutron diffraction and ab initio calculations revealed the crystal structure and magnetic configuration which could not be determined from the X-ray diffraction and magnetic measurements. As reported earlier, Rietveld refinement of neutron diffraction data confirmed L21 structure for Mn2VGa and Xa structure for Mn2CoGa. The alloys with x=0.25 and 0.5 possess L21 structure with Mn(C)-Co disorder. As the Co concentration reaches 0.75, a structural transition has been observed from disordered L21 to disordered Xa. Detailed ab initio studies also confirmed this structural transition. The reason for the magnetic moment compensation in Mn2(V1-xCox)Ga was identified to be different from that of the earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of neutron diffraction and ab initio studies, it is identified that the disordered L21 structure with antiparallel coupling between the ferromagnetically aligned magnetic moments of (Mn(A)-Mn(C)) and (V-Co) atom pairs enables the compensation in Mn2V1-xCoxGa.",2001.00707v1 2020-08-11,Effect of doping on SGS and weak half-metallic properties of inverse Heusler Alloys,"Heusler alloys with Mn and Co have been found to exhibit interesting electronic and magnetic properties. Mn$_2$CoAl is well known SGS compound while Mn$_2$CoGa has weak half metallic character. By using plane wave pseudo-potential method, we studied the effect of Fe and Cr doping on half-metalicity and magnetism of these compounds. The doping destroys the SGS nature of Mn$_2$CoAl while the small-scale doping enhance the half-metallicity of Mn$_2$CoGa making it perfect half-metal. In case of Mn$_2$CoAl, the doping decrease the band gap while increase in band width is noticed for Mn$_2$CoGa. The half-metallicity is destroyed in both cases when the doping level is beyond certain degree. Moreover, we have also computed magnetic behavior of Mn$_2$CoZ alloys and we found that total magnetic moments of dopped samples have higher values than that of pristine compounds.",2008.04536v1 2018-04-23,"Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations","Structural, electronic, and transport properties of ScNiSb, ScPdSb, and ScPtSb were investigated from first principles. Electronic band structures derived within the fully relativistic MBJLDA approach were compared with those obtained from the standard GGA calculations. All the compounds studied exhibit indirect narrow band gaps (0.24-0.63 eV). The effective masses of hole-like carriers are relatively small (0.27-0.36), and decrease with an increasing atomic number of the transition metal component. The carrier relaxation time, required for realistic calculations of the electrical conductivity, was approximated within the deformation potential theory. The GGA approach yielded overestimated transport characteristics with respect to those derived within the MBJLDA analysis. The largest power factor of 4-6 mWK^-2m^-1 ) at high temperatures was obtained for ScPtSb. This value is comparable with those observed experimentally for Fe-Nb-Sb half-Heusler alloys, and hence makes ScPtSb a very good candidate material for thermoelectric applications.",1804.08423v1 2019-08-16,Scaling Analysis of Anomalous Hall Resistivity in the Co$_{2}$TiAl Heusler Alloy,"A comprehensive magnetotransport study including resistivity ($\rho_{xx}$) at various fields, isothermal magnetoresistance and Hall resistivity ($\rho_{xy}$) has been carried out at different temperatures on the Co$_{2}$TiAl Heusler alloy. Co$_{2}$TiAl alloy shows a paramagnetic (PM) to ferromagnetic (FM) transition below the curie temperature (T$_{C}$) $\sim$ 125 K. In the FM region, resistivity and magnetoresistance reveals a spin flip electron-magnon scattering and the Hall resistivity unveils the anomalous Hall resistivity ($\rho_{xy}^{AH}$). Scaling of anomalous Hall resistivity with resistivity establishes the extrinsic scattering process responsible for the anomalous hall resistivity; however Skew scattering is the dominant mechanism compared to the side-jump contribution. A one to one correspondence between magnetoresistance and side-jump contribution to anomalous Hall resistivity verifies the electron-magnon scattering being the source of side-jump contribution to the anomalous hall resistivity.",1908.05974v1 2021-06-25,"First-principles investigation of half-metallic ferromagnetism of Fe$_2$YSn (Y = Mn, Ti and V) Heusler alloys","In this paper, we use the first-principles calculations based on the density functional theory to investigate structural, electronic and magnetic properties of Fe$_{2}$YSn with (Y = Mn, Ti and V). The generalized gradient approximation (GGA) method is used for calculations. The Cu$_{2}$MnAl type structure is energetically more stable than the Hg$_{2}$CuTi type structure. The negative formation energy is shown as the evidence of thermodynamic stability of the alloy. The calculated total spin moment is found as 3$\mu_\text{B}$ and 0$\mu_\text{B}$ at the equilibrium lattice constant for Fe$_{2}$MnSn and Fe$_{2}$TiSn respectively, which agrees with the Slater-Pauling rule of $M_t= Z_t-24$. The study of electronic and magnetic properties proves that Fe$_{2}$MnSn and Fe$_{2}$TiSn full-Heusler alloys are complete half-metallic ferromagnetic materials.",2106.13604v1 2021-08-11,Critical Magnetic Behavior of the Half Heusler Alloy RhCrSi: Monte Carlo Study,"In this paper, we study the critical magnetic properties of the Half Heusler alloy RhCrSi, using Monte Carlo simulations (MCS) under the Metropolis algorithm. In fact, to study this alloy, we apply an Ising model using the MCS simulations, we concentrate only on the magnetic atoms: Rh and Cr. For this purpose, these magnetic atoms are modeled by the spin moments S=5/2 for Rh atoms and sigma=2 for Cr atoms, respectively. In addition, we discuss the ground state phase diagrams in different planes corresponding to different physical parameters. On the other hand, for non-null temperature values, we perform the Monte Carlo simulations (MCS) to study the critical behavior of the compound RhCrSi, in the Ising approximation. Indeed, we present a detailed discussion of the obtained results for the magnetizations as a function of the temperature, the crystal field and the exchange coupling interactions. Additionally, we give the reliance of the basic temperature as an element of precious crystal field when fixing the exchange coupling interactions. To finish this work, we built up and examined the magnetic hysteresis cycles and the relating coercive fields as a part of the external magnetic field.",2108.05162v1 2023-02-15,"Magnetic phase diagram of the austenitic Mn-rich Ni-Mn-(In,Sn) Heusler alloys","Heusler compounds have been intensively studied owing to the important technological advancements that they provide in the field of shape memory, thermomagnetic energy conversion and spintronics. Many of their intriguing properties are ultimately governed by their magnetic states and understanding and possibly tuning them is evidently of utmost importance. In this work we examine the \alloys alloys with Density Functional Theory simulations and $^{55}$Mn Nuclear Magnetic Resonance and combine these two methods to carefully describe their ground state magnetic order. In addition, we compare the results obtained with the conventional generalized gradient approximation with the ones of strongly constrained and appropriately normed (SCAN) semilocal functionals for exchange and correlation. Experimental results eventually allow to discriminate between two different scenarios identified by ab initio simulations.",2302.07550v1 2008-10-29,Thermodynamics of the Heusler alloy Co_2-xMn_1+xSi: a combined density functional theory and cluster expansion study,"Previous studies indicated that intrinsic point defects play a crucial role for the density of states of ferromagnetic half-metals in the band gap region: At large concentrations, defect-derived bands might close the gap at the Fermi energy in the minority spin channel. In this work, structural disorder in the Co- and Mn-sublattices of the full Heusler alloy Co_2-xMn_1+xSi (-1 < x < 2) is investigated with a cluster expansion approach, parametrized using all-electron density functional theory calculations. By establishing two separate cluster expansions, one for the formation energy and one for the total spin moment, we are in position to determine the stability of different configurations, to predict new (also half-metallic) ground states and to extend the known Slater-Pauling rule for ideally stoichiometric Heusler alloys to non-stoichiometric, Mn-rich compositions. This enables us to identify potentially half-metallic structures in the Mn-rich region. With the help of Monte Carlo simulations based on the cluster expansion, we establish theoretically that Co_2-xMn_1+xSi close to the stoichiometric composition ought to show a high degree of structural order in thermodynamic equilibrium. Hence, samples prepared with the correct stoichiometry should indeed be half-metallic after thermal annealing. Moreover, we predict that adding a small amount of Mn to stoichiometric Co_2MnSi allows to suppress the thermally activated formation of detrimental Co antisites. At Mn-rich compositions (x>1), the ordered ground state structures predicted for zero temperature are found to be thermally unstable and to decompose into Co2MnSi and Mn3Si above room temperature.",0810.5354v2 2014-10-01,Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy,"Spin gapless semiconductors (SGS) form a new class of magnetic semiconductors, which has a band gap for one spin sub band and zero band gap for the other, and thus are useful for tunable spin transport based applications. In this paper, we report the first experimental evidence for spin gapless semiconducting behavior in CoFeMnSi Heusler alloy. Such a behavior is also confirmed by first principles band structure calculations. The most stable configuration obtained by the theoretical calculation is verified by experiment. The alloy is found to crystallize in the cubic Heusler structure (LiMgPdSn type) with some amount of disorder and has a saturation magnetization of 3.7 Bohr's magneton/f.u.. and Curie temperature of 620 K. The saturation magnetization is found to follow the Slater-Pauling behavior, one of the prerequisites for SGS. Nearly temperature-independent carrier concentration and electrical conductivity is observed from 5 to 300 K. An anomalous Hall coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection data has yielded the current spin polarization value of 0.64, which is found to be robust against the structural disorder. All these properties are quite promising for the spintronic applications such as spin injection and can bridge a gap between the contrasting behavior of half-metallic ferromagnets and semiconductors.",1410.0177v1 2019-03-11,Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys,"Shell ferromagnetism is a new functional property of certain Heusler alloys which has been recently observed in $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$. We report the results of a comparative study of the magnetic microstructure of bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys using magnetometry, synchrotron x-ray diffraction, and magnetic small-angle neutron scattering (SANS). By combining unpolarized and spin-polarized SANS (POLARIS) we demonstrate that a number of important conclusions regarding the mesoscopic spin structure can be made. In particular, the analysis of the magnetic neutron data suggests that nanoprecipitates with an effective ferromagnetic component form in an antiferromagnetic matrix on field annealing at $700 \, \mathrm{K}$. These particles represent sources of perturbation, which seem to give rise to magnetically disordered regions in the vicinity of the particle-matrix interface. Analysis of the spin-flip SANS cross section via the computation of the correlation function yields a value of $\sim 55 \, \mathrm{nm}$ for the particle size and $\sim 20 \, \mathrm{nm}$ for the size of the spin-canted region.",1903.04183v1 2021-05-05,Rhodium based half-Heusler alloys as possible optoelectronic and thermoelectric materials,"On the basis of density functional theory and semi-classical Boltzmann theory, we have investigated the structural, elastic, electronic, optical and thermoelectric properties of 18--valence electron count rhodium based half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The absence of imaginary frequencies in the phonon dispersion curve for these system verifies that they are structurally stable. RhTiP is ductile in nature, while others are brittle. The alloys are found to be semiconducting with indirect band gaps ranging from 0.94 to 1.01 eV. Our calculations suggest these materials to have high absorption coefficient and optical conductivity in the ultraviolet as well as visible region. While considering thermoelectricity, we found that $p$--type doping is more favorable in improving the thermoelectric properties. The calculated values of power factor with $p$-type doping are comparable to some of the reported half-Heusler materials. The optimum figure of merit \zt\ is $\sim1$ for RhTiBi suggesting it as a promising candidate for thermoelectric applications while RhTiP, RhTiAs, and RhTiSb with optimum \zt \ values between 0.38 to 0.67 are possible candidates for use in thermoelectric devices.",2105.02177v1 2022-04-07,"First Principles Study of the Structural, Mechanical, Electronic, and Lattice Dynamical Properties of the Half-Heusler Alloys ZrCoY (Y=Sb, Bi )","First-principles calculation has led to significant discoveries in materials science. Half heusler (HH) alloys, which are potential thermoelectric materials have demonstrated significant improvements in thermoelectric performance owing to their thermal stability, mechanical strength, and moderate ZT. Using Density Functional Theory (DFT), the structural, mechanical, electronic, and lattice dynamical properties of cubic Half Heusler alloys ZrCoY (Y=Sb, Bi) have been investigated. The unknown exchange-correlation functional is approximated using the generalized gradient approximation (GGA) pseudopotential plane-wave approach. The structural parameters, that is, equilibrium lattice constant, elastic constants, and their derivatives are consistent with reported experimental and theoretical studies where available. Mechanical properties such as anisotropy factor A, shear modulus G, bulk modulus B, Youngs modulus E, and Poisons ratio n, are calculated using the Voigt-Reuss-Hill average approach based on elastic constants. The Debyes temperature, as well as longitudinal and transverse sound velocities, are predicted from elastic constants at GGA-PBE and GW approximations. The study of elastic constants showed that the compounds are mechanically stable, and the phonon dispersion study showed that they are dynamically stable as well. The ductility and anisotropic nature of the compounds are confirmed by the elastic constants and mechanical properties.",2204.03759v1 2023-03-08,Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa,"Spin semimetals are amongst the most recently discovered new class of spintronic materials, which exhibit a band gap in one spin channel and semimetallic feature in the other, thus facilitating tunable spin transport. Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along with giant coercivity and spin-valve characteristics using a combined experimental and theoretical study. The alloy crystallizes in an inverse Heusler structure (without any martensitic transition) with a para- to ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient, relatively low magnitude and weak temperture dependance of electrical resistivity suggest the semimetallic character of the alloy. This is further supported by our specific heat measurement. Magnetoresistance (MR) confirms an irreversible nature (with its magnitude $\sim$1\%) along with a change of sign across the magnetic transition indicating the potentiality of Mn$_2$IrGa in magnetic switching applications. In addition, asymmetric nature of MR in the positive and negative field cycles is indicative of spin-valve characteristics. Our ab-initio calculations confirm the inverse Heusler structure with ferrimagnetic ordering to be the lowest energy state, with a saturation magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic axis with considerable magneto-crystalline anisotropy energy. A large positive Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall conductivity ($\sim$-180 S/cm).",2303.04649v2 2023-07-18,Effect of Spin Orbit Coupling in non-centrosymmetric half-Heusler alloys,"Spin-orbit coupled electronic structure of two representative non-polar half-Heusler alloys, namely 18 electron compound CoZrBi and 8 electron compound SiLiIn have been studied in details. An excursion through the Brillouin zone of these alloys from one high symmetry point to the other revealed rich local symmetry of the associated wave vectors resulting in non-trivial spin splitting of the bands and consequent diverse spin textures in the presence of spin-orbit coupling. Our first principles calculations supplemented with low energy $\boldsymbol{k.p}$ model Hamiltonian revealed the presence of linear Dresselhaus effect at the X point having $D_{2d}$ symmetry and Rashba effect with both linear and non-linear terms at the L point with $C_{3v}$ point group symmetry. Interestingly we have also identified non-trivial Zeeman spin splitting at the non-time reversal invariant W point and a pair of non-degenerate bands along the path $\Gamma$ to L displaying vanishing spin polarization due to the non-pseudo polar point group symmetry of the wave vectors. Further a comparative study of CoZrBi and SiLiIn suggest, in addition, to the local symmetry of the wave vectors, important role of the participating orbitals in deciding the nature and strength of spin splitting. Our calculations identify half-Heusler compounds with heavy elements displaying diverse spin textures may be ideal candidate for spin valleytronics where spin textures can be controlled by accessing different valleys around the high symmetry k-points.",2308.03760v2 2020-04-04,Improved crystallographic compatibility and magnetocaloric reversibility in Pt substituted Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy,"We present here the improved crystallographic/geometric compatibility and magnetocaloric reversibility by measurement of magnetic entropy change using different protocols in 10% Pt substituted Ni2Mn1.4In0.6 magnetic shape memory alloy. The substitution of Pt reduces the thermal hysteresis about 50% to the Ni2Mn1.4In0.6. The origin of the reduced thermal hysteresis is investigated by the crystallographic compatibility of the austenite and martensite phases. The calculated middle eigenvalue of the transformation matrix turned out to be 0.9982, which is very close to 1 (deviation is only 0.18%) suggests for the crystallographic compatibility between the austenite and martensite phases in Ni1.9Pt0.1Mn1.4In0.6. A very small thermal hysteresis and crystallographic compatibility between two phases in this alloy system indicate a stress-free transition layer (i.e. perfect habit plane) between the austenite and martensite phase, which is expected to give reversible martensite phase transition and therefore reversible magnetocaloric effect (MCE) as well. The calculated value of the isothermal entropy change ({\Delta}Siso) using the magnetization curve under three different measurement protocols (i.e. isothermal, loop, and isofield measurement protocol) is found to be nearly same indicating a reversible MCE in the present alloy system. Our work provides a path to design new magnetic shape memory Heusler alloys for magnetic refrigeration and also suggest that any of the above measurement protocol can be used for the calculation of {\Delta}Siso for materials satisfying geometrical compatibility condition.",2004.01854v1 2017-06-06,"Structural, electronic, magnetic and transport properties of equiatomic quaternary Heusler Alloy CoRhMnGe: Theory and Experiment","In this work, we present structural, electronic, magnetic, mechanical and transport properties of equiatomic quaternary Heusler alloy, CoRhMnGe using both theoretical and experimental techniques. A detailed structural analysis is performed using X-ray diffraction(XRD) and extended X-ray absorption fine structure(EXAFS) spectroscopy. The alloy is found to crystallize in Y-type structure having space group $F\bar{4}3m$ (\# 216). The ab-initio simulation pedict half-metallic ferromagnetic characteristics leading to large spin polarization. The calculated magnetization is found to be in fair agreement with experiment as well as those predicted by the Slater-Pauling rule, which is a prerequisite for half-metallicity. The magnetic transition temperature($\mathrm{T_{C}}$) is found to be $\sim 760$ K. Measured electrical resistivity in the temperature range 2-400 K also gives an indication of half-metallic behavior. Simulated resistivity matches fairly well with those measured, with the temperature dependant carrier relaxation time lying in the range $1-2$ fs. Effect of hydrostatic pressure on electronic structure, magnetic and mechanical properties are investigated in detail. The alloy is found to preserve half-metallic characteristics upto 30.27 GPa beyond which it transit to metallic phase. No magnetic phase transition is found to occur in the whole range of pressure. The system also satisfies the Born-Huang criteria for mechanical stability upto a limited range of pressure. All these properties make CoRhMnGe alloy promising for spintronics devices.",1706.01624v1 2023-06-26,Large saturation moment and high ferromagnetic transition temperature in a structurally disordered inverse Heusler alloy Fe2RuGe,"We report the successful synthesis of a new 4$d$ based polycrystalline inverse Heusler alloy Fe$_2$RuGe by an arc melting process and have studied in detail its structural, magnetic and transport properties complemented with first principle calculations. X-ray and neutron diffraction, Extended X-ray Absorption Fine Structure and $^{57}$Fe M\""{o}ssbauer spectroscopic studies confirm the single phase nature of the system where the Fe and Ru atoms are randomly distributed in the 4$c$ and 4$d$ Wyckoff positions in a ratio close to 50:50. The formation of the disordered structure is also confirmed by the theoretical energy minimization calculation. Despite the random cross-site disorder of Fe and Ru atoms, magnetic measurements suggest not only a high Curie temperature of $\sim$860\,K, but also a large saturation magnetic moment $\sim$4.9\,$\mu_B$ per formula unit at 5\,K, considerably exceeding the theoretical limit (4\,$\mu_B$ per formula unit) predicted by the Slater-Pauling rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high Curie temperatures. Neutron diffraction analysis coupled with the isothermal magnetization value indicates that the magnetic moments in Fe$_2$RuGe are associated with Fe-atoms only, which is also confirmed by M\""ossbauer spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of the parent compound, Fe$_3$Ge, the Curie temperature of Fe$_2$RuGe has increased significantly despite the substitution of the nonmagnetic, yet isoelectronic element Ru in this structurally disordered compound. Our theoretical calculation reveals that the large Fe moment ($\sim2.8\mu_B$/Fe) on the 4$b$ site can be attributed to a charge transfer from this Fe site towards its Ru neighbours. Such a substantial increase in magnetic moment due to electron charge transfer has not previously been reported in a Heusler alloy system.",2306.14831v1 2013-11-04,Magnetic interactions in the Martensitic phase of Mn rich Ni-Mn-In shape memory alloys,"The magnetic properties of Mn$_{2}$Ni$_{(1+x)}$In$_{(1-x)}$ ($x$ = 0.5, 0.6, 0.7) and Mn$_{(2-y)}$Ni$_{(1.6+y)}$In$_{0.4}$ ($y$ = -0.08, -0.04, 0.04, 0.08) shape memory alloys have been studied. Magnetic interactions in the martensitic phase of these alloys are found to be quite similar to those in Ni$_2$Mn$_{(1+x)}$In$_{(1-x)}$ type alloys. Doping of Ni for In not only induces martensitic instability in Mn$_2$NiIn type alloys but also affects magnetic properties due to a site occupancy disorder. Excess Ni preferentially occupies X sites forcing Mn to the Z sites of X$_2$YZ Heusler composition resulting in a transition from ferromagnetic ground state to a state dominated by ferromagnetic Mn(Y) - Mn(Y) and antiferromagnetic Mn(Y)-Mn(Z) interactions. These changes in magnetic ground state manifest themselves in observation of exchange bias effect even in zero field cooled condition and virgin magnetization curve lying outside the hysteresis loop.",1311.0579v1 2017-01-30,Effect of site occupancy disorder on Martensitic properties of Mn$_{2}$NiIn type alloys: x-ray absorption fine structure study,"We have carried out \textit{ab-initio} calculations of local structure of Mn and Ni in Mn$_{2}$Ni$_{1.5}$In$_{0.5}$ alloy with different site occupancies in order to understand the similarities in martensitic and magnetic properties of Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ and Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Our results show that in Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ alloys there is a strong possibility of Mn atoms occupying all the three, X, Y and Z sites of X$_2$YZ Heusler structure while Ni atoms preferentially occupy the X sites. Such a site occupancy disorder of Mn atoms is in addition to a local structural disorder due to size differences between Mn and In atoms which is also present in Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Further, a comparison of the calculations with experimental XAFS at the Mn and Ni K edges in Mn$_{2-y}$Ni$_{1.6+y}$In$_{0.4}$ ($-0.08 \le y \le 0.08$) indicate a strong connection between martensitic transformation and occupancy of Z sites by Mn atoms.",1701.08561v1 2019-11-09,Multi-Principal-Element Approach to High-Performance Thermoelectric Materials,"High-entropy alloys are characterized by high configurational entropy. Since the discovery of high-entropy alloys (HEA) in 2004, entropy engineering has provided a promising direction for exploiting composition, lattice disorder, band structure, and microstructure effects to advance thermoelectric performance. This review discusses the impact of entropy on thermoelectric properties and looks back at the role of multi-principal-element alloys, a weaker version of HEA, on the development of compositionally complex thermoelectric alloys in achieving high thermoelectric performance. The experimental and theoretical efforts in a wide range of material systems such as TAGS, LAST, half-Heusler, liquid-like copper chalcogenides, SnTe, and CuInTe2 chalcopyrites provide insights into the entropy engineering approach and also promise an emerging paradigm of high-entropy thermoelectrics.",1911.03797v1 2019-07-05,Thermoelectric transport trends in group 4 half-Heusler alloys,"The thermoelectric properties of 54 different group 4 half-Heusler (HH) alloys have been studied from first principles. Electronic transport was studied with density functional theory using hybrid functionals facilitated by the $\mathbf{k} \cdot \mathbf{p}$ method, while the temperature dependent effective potential method was used for the phonon contributions to the figure of merit $ZT$. The phonon thermal conductivity was calculated including anharmonic phonon-phonon, isotope, alloy and grain-boundary scattering. HH alloys have an ${\it XYZ}$ composition and those studied here are in the group 4-9-15 (Ti,Zr,Hf)(Co,Rh,Ir)(As,Sb,Bi) and group 4-10-14 (Ti,Zr,Hf)(Ni,Pd,Pt)(Ge,Sn,Pb). The electronic part of the thermal conductivity was found to significantly impact $ZT$ and thus the optimal doping level. Furthermore, the choice of functional was found to significantly affect thermoelectric properties, particularly for structures exhibiting band alignment features. The intrinsic thermal conductivity was significantly reduced when alloy and grain boundary scattering were accounted for, which also reduced the spread in thermal conductivity. It was found that sub-lattice disorder on the ${\it Z}$-site, i.e. the site occupied by group 14 or 15 elements, was more effective than ${\it X}$-site substitution, occupied by group 4 elements. The calculations confirmed that ZrNiSn, ZrCoSb and ZrCoBi based alloys display promising thermoelectric properties. A few other n-type and p-type compounds were also predicted to be potentially excellent thermoelectric materials, given that sufficiently high charge carrier concentrations can be achieved. This study provides insight into the thermoelectric potential of HH alloys and casts light on strategies to optimize thermoelectric performance of multicomponent alloys.",1907.02845v1 2019-03-18,"Experimental and Theoretical Investigation on the Possible Half-metallic Behaviour of Equiatomic Quaternary Heusler Alloys: CoRuMnGe and CoRuVZ (Z = Al, Ga)","In this report, structural, electronic, magnetic and transport properties of quaternary Heusler alloys CoRuMnGe and CoRuVZ (Z = Al, Ga) are investigated. All the three alloys are found to crystallize in cubic structure. CoRuMnGe exhibits L2$_1$ structure whereas, the other two alloys have B2-type disorder. For CoRuMnGe and CoRuVGa, the experimental magnetic moments are in close agreement with the theory as well as those predicted by the Slater-Pauling rule, while for CoRuVAl, a relatively large deviation is seen. The reduction in the moment in case of CoRuVAl possibly arises due to the anti-site disorder between Co and Ru sites as well as V and Al sites. Among these alloys, CoRuMnGe has the highest T$\mathrm{_C}$ of 560 K. Resistivity variation with temperature reflects the half-metallic nature in CoRuMnGe alloy. CoRuVAl shows metallic character in both paramagnetic and ferromagnetic states, whereas the temperature dependence of resistivity for CoRuVGa is quite unusual. In the last system, $\rho$ vs. T curve shows an anomaly in the form of a maximum and a region of negative temperature coefficient of resistivity (TCR) in the magnetically ordered state. The ab initio calculations predict nearly half-metallic ferromagnetic state with high spin polarization of 91, 89 and 93 \% for CoRuMnGe, CoRuVAl and CoRuVGa respectively. To investigate the electronic properties of the experimentally observed structure, the Co-Ru swap disordered structures of CoRuMnGe alloy are also simulated and it is found that the disordered structures retain half-metallic nature, high spin polarization with almost same magnetic moment as in the ideal structure. Nearly half-metallic character, high T$\mathrm{_C}$ and high spin polarization make CoRuMnGe alloy promising for room temperature spintronic applications.",1903.07265v2 2005-05-11,"Above-room-temperature ferromagnetism in half-metallic Heusler compounds NiCrP, NiCrSe, NiCrTe and NiVAs: A first-principles study","We study the interatomic exchange interactions and Curie temperatures in half-metallic semi Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study is performed within the framework of density functional theory. The calculation of exchange parameters is based on the frozen-magnon approach. It is shown that the exchange interactions in NiCrZ vary strongly depending on the Z constituent. The Curie temperature, Tc, is calculated within the mean field and random phase approximations. The difference between two estimations is related to the properties of the exchange interactions. The predicted Curie temperatures of all four systems are considerably higher than room temperature. The relation between the half-metallicity and the value of the Curie temperature is discussed. The combination of a high spin-polarization of charge carriers and a high Curie temperature makes these Heusler alloys interesting candidates for spintronics applications.",0505299v1 2006-11-17,Electronic structure of half-metallic magnets,"We have analyzed the electronic structure of half-metallic magnets based on first principles electronic structure calculations of a series of semi-Heusler alloys. The characteristic feature of the electronic structure of semi-Heusler systems is a d-d gap in the density of states lying at/close to the Fermi level depending on the number of valence electrons. We have employed various indicators of chemical bonding to understand the origin of the gap in these systems, which is crucial for their half-metallic property. The density of states of other half-metallic magnets also supports a gap and it is a generic feature of these systems. We have discussed in some details the origin of magnetism, in particular, how the presence of the gap is crucial to stabilize half-metallic ferro and ferri magnetism in these systems. Finally, we have studied the role of magnetic impurities in semiconducting semi-Heusler systems. We show with the aid of model supercell calculations that these systems are not only ferromagnetic but also half-metallic with possibly high Curie temperature.",0611476v1 2013-04-12,Crossover of magnetoresistance in the zerogap half-metallic Heusler alloy Fe2CoSi,"This work reports on the band structure and magneto-transport investigations of the inverse Heusler compound Fe2CoSi. The first-principles calculations reveal that Fe2CoSi has a very peculiar band structure with a conducting property in the majority spin channel and a nearly zero bandgap in the minority spin channel. The synthesized Fe2CoSi sample shows a high-ordered inverse Heusler structure with a magnetic moment of 4.88 {\mu}B at 5 K and a high Curie temperature of 1038 K. With increasing temperature, a crossover from positive to negative magnetoresistance (MR) is observed. Complemented with the Hall effect measurements, we suggest the intriguing crossover of MR can be ascribed to the dominant spin carriers changing from the gapless minority spin channel to the majority spin channel at Fermi level.",1304.3517v1 2013-04-16,Kinetic arrest related to a first-order ferrimagnetic to antiferromagnetic transition in the Heusler compound Mn2PtGa,"We report a magnetization study of the Heusler compound Mn2PtGa that shows the existence of a magnetic-glass state. Mn2PtGa shows a first-order ferromagnetic (FM)/ferrimagnetic (FI) to antiferromagnetic (AFM) transition in contrast to the martensitic structural transition observed in several Heusler alloys. The kinetic arrest of this first-order FM (FI) to AFM transition leads to the observed magnetic-glass behavior. We show that the strength of the applied magnetic field, which is the primary parameter to induce the magnetic-glass state, is also responsible for the stability of the supercooled FM (FI) phase in time.",1304.4459v1 2013-09-24,"Electronic structure and magnetism of new scandium-based full Heusler compounds: Sc2CoZ (Z=Si, Ge, Sn)","First principles FPLAPWcalculations were performed in the framework of Density Functional Theory (DFT), to study the electronic structures and magnetic properties for the new full-Heusler compounds: Sc2CoZ (Z=Si, Ge, Sn). The investigated materials are stable against decomposition, in ferromagnetic configuration and crystallize in the inverse Heusler structures. The half-metallic properties as function of the variation of unit cell volumes are analysed regarding the fourth main group constituent elements. The electronic structure calculations for Sc2CoSi and Sc2CoSn show half-metallic characters, with indirect band gaps of 0.544 eV and 0.408 eV at optimized lattice parameters of 6.28 A and 6.62 A, respectively. For Sc2CoGe compound, the Fermi energy is not pinned inside the energy band gap from minority density of states, neither for unit cell contraction or for enlargement. The calculated total magnetic moments are 1muB/f.u., for all compounds, in agreement with Slater-Pauling rule.",1309.6256v3 2018-10-11,Unconventional transport behavior in the Quaternary Heusler compounds CoFeTiSn and CoFeVGa,"We report here the electrical transport and magnetic properties of the newly synthesized quaternary Heusler compound CoFeTiSn and CoFeVGa. We observe a striking change in the electronic transport properties of CoFeTiSn as the system undergoes the paramagnetic to ferromagnetic transition. While the sample shows an activated semiconducting behaviour in the paramagnetic phase, it turns abruptly to a metallic phase with the onset of ferromagnetic transition. We have compared the system with other Hesuler compounds showing similar anomaly in transport, and it appears that CoFeTiSn has much similarities with the Fe$_2$VAl compound having pseudogap in the paramagnetic phase. In sharp contrast, CoFeVGa shows a predominantly semiconducting behaviour down to 90 K, below which it shows a window of metallic region. Both the compositions show negative Seebeck coefficient varying linearly with temperature. The value of the Seebeck coefficient of CoFeTiSn is comparable to that of many Heusler alloys identified as potential thermoelectric materials.",1810.04865v1 2019-04-03,Observation of Topological Hall Effect and Signature of Room Temperature Antiskyrmions in Mn-Ni-Ga D2d Heusler magnets,"Topologically stable nontrivial spin structures, such as skyrmions and antiskyrmions, display a large topological Hall effect owing to their quantized topological charge. Here, we present the finding of a large topological Hall effect beyond room temperature in the tetragonal phase of a Mn-Ni-Ga based ferrimagnetic Heusler shape memory alloy system. The origin of the field induced topological phase, which is also evidenced by the appearance of dips in the ac-susceptibility measurements, is attributed to the presence of magnetic antiskyrmions driven by D2d symmetry of the inverse Heusler tetragonal phase. Detailed micromagnetic simulations asserts that the antiskyrmionic phase is stabilized as a result of interplay among inhomogeneous Dzyaloshinskii-Moriya interaction, the Heisenberg exchange, and the magnetic anisotropy energy. The robustness of the present result is demonstrated by stabilizing the antiskyrmion hosting tetragonal phase up to a temperature as high as 550 K by marginally varying the chemical composition, thereby driving us a step closer to the realization of ferrimagnetic antiskyrmion based racetrack memory.",1904.01894v1 2024-03-12,Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization,"Magnetic random access memory that uses magnetic tunnel junction memory cells is a high performance, non-volatile memory technology that goes beyond traditional charge-based memories. Today its speed is limited by the high magnetization of the memory storage layer. Here we show that fast and highly reliable switching is possible using a very low magnetization ferrimagnetic Heusler alloy, Mn3Ge. Moreover, the tunneling magnetoresistance is the highest yet achieved for a ferrimagnetic material at ambient temperature. Furthermore, the devices were prepared on technologically relevant amorphous substrates using a novel combination of a nitride seed layer and a chemical templating layer. These results show a clear path to the lowering of switching currents using ferrimagnetic Heusler materials and, therefore, to the scaling of high performance magnetic random access memories beyond those nodes possible with ferromagnetic devices.",2403.08112v1 2001-03-23,Premartensitic Transition in Ni2+xMn1-xGa Heusler Alloys,"The temperature dependencies of the resistivity and magnetization of a series of Ni2+XMn1-XGa (X = 0 - 0.09) alloys were investigated. Along with the anomalies associated with ferromagnetic and martensitic transitions, well-defined anomalies were observed at the temperature of premartensitic transformation. The premartensitic phase existing in a temperature range 200 - 260 K in the stoichiometric Ni2MnGa is suppressed by the martensitic phase with increasing Ni content and vanishes in Ni2.09Mn0.91Ga composition.",0103483v1 2002-02-27,Electronic Structure and Charge Dynamics of Huesler Alloy Fe2TiSn Probed by Infrared and Optical Spectroscopy,"We report on the electrodynamics of a Heusler alloy Fe2TiSn probed over four decades in energy: from the far infrared to the ultraviolet. Our results do not support the suggestion of Kondo-lattice behavior inferred from specific heat measurements. Instead, we find a conventional Drude-like response of free carriers, with two additional absorption bands centered at around 0.1 and 0.87 eV. The latter feature can be interpreted as excitations across a pseudogap, in accord with band structure calculations.",0202512v2 2004-07-07,"A critical discussion of calculated modulated structures, Fermi surface nesting and phonon softening in magnetic shape memory alloys Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge)","A series of first principles calculations have been carried out in order to discuss electronic structure, phonon dynamics, structural instabilities and the nature of martensitic transformations of the Heusler alloys Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge). The calculations show that besides electronic pecularities like Fermi--surface nesting, hybridizing optical and acoustic phonon modes are important for the stabilization of the modulated martensitic structures.",0407157v1 2007-11-19,Room Temperature Magnetocaloric Effect in Ni-Mn-In,"We have studied the effect of magnetic field on a non-stoichiometric Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$ that undergoes a martensitic as well as a magnetic transition near room temperature. Temperature dependent magnetization measurements demonstrate the influence of magnetic field on the structural phase transition temperature. From the study of magnetization as a function of applied field, we show the occurrence of inverse-magnetocaloric effect associated with this magneto-structural transition. The magnetic entropy change attains a value as high as 25 J/kg-K (at 5 T field) at room temperature as the alloy transforms from the austenitic to martensitic phase with a concomitant magnetic ordering.",0711.2896v1 2017-07-26,Magnetism from intermetallics and perovskite oxides,"This work has been presented by RJCV to obtain his PhD degree at Fluminense Federal University, in March of 2017. We focused on the synthesis of compounds and then on their magneto-strucutral characterization; mainly due to the interplay of these physical properties. We have prepared intermetallic alloys (including Heusler alloys) and perovskite oxides (manganites and cobaltites); in bulk and nanoparticles. A thorough analysis of the influence of the morphology and crystal structure on the magnetic properties of these compounds is addressed.",1707.09868v2 2016-12-22,Ab initio Study of Effect of Co Substitution on the Magnetic Properties of Ni and Pt-based Heusler Alloys,"Using density functional theory based calculations, we have carried out in-depth studies of effect of Co substitution on the magnetic properties of Ni and Pt-based shape memory alloys. We show the systematic variation of the total magnetic moment, as a function of Co doping. A detailed analysis of evolution of Heisenberg exchange coupling parameters as a function of Co doping has been presented here. The strength of RKKY type of exchange interaction is found to decay with the increase of Co doping.",1612.07518v1 2007-07-05,"Engineering the electronic, magnetic and gap-related properties of the quinternary half-metallic Heusler alloys","We review the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co$_2$[Cr$_{1-x}$Mn$_x$][Al$_{1-y}$Si$_y$] employing three different approaches : (i) the coherent potential approximation (CPA), (ii) the virtual crystal approximation (VCA), and (iii) supercell calculations (SC). All three methods give similar results and the local environment manifested itself only for small details of the density of states. All alloys under study are shown to be half-metals and their total spin moments follow the so-called Slater-Pauling behavior of the ideal half-metallic systems. We especially concentrate on the properties related to the minority-spin band-gap. We present the possibility to engineer the properties of these alloys by changing the relative concentrations of the low-valent transition metal and $sp$ atoms in a continuous way. Our results show that for realistic applications, ideal are the compounds rich in Si and Cr since they combine large energy gaps (around 0.6 eV), robust half-metallicity with respect to defects (the Fermi level is located near the middle of the gap) and high values of the majority-spin density of states around the Fermi level which are needed for large values of the perfectly spin-polarized current in spintronic devices like spin-valves or magnetic tunnel junctions.",0707.0728v1 2015-01-22,High spin polarization and large spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy,"In this paper, we investigate CoFeCrAl alloy by means of various experimental techniques and ab-initio calculations to look for half-metallic nature. The alloy is found to exist in the cubic Heusler structure, with presence of B2 ordering. Saturation magnetization (MS) value of about 2 Bohr magneton/f.u. is observed at 8 K under ambient pressure, which is in good agreement with the Slater-Pauling rule. MS values are found to be independent of pressure, which is a prerequisite for half-metals. The ab-initio electronic structure calculations predict half-metallic nature for the alloy with a spin slitting energy of 0.31 eV. Importantly, this system shows a high current spin polarization value of 0.67 [with error of 0.02], as deduced from the point contact Andreev reflection (PCAR) measurements. Linear dependence of electrical resistivity with temperature indicates the possibility of reasonably high spin polarization at elevated temperatures (~150 K) as well. All these suggest that CoFeCrAl is a promising material for the spintronic devices.",1501.05599v1 2017-12-05,Peculiarities of the electronic transport in half-metallic Co-based Heusler alloys,"Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co$_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn, Sb) were studied in the temperature range 4.2--900 K and in magnetic fields of up to 100 kOe. It was found that varying Y in affects strongly the electric resistivity and its temperature dependence $\rho(T)$, while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in $\rho(T)$ near the Curie temperature $T_C$. At $T < T_C$, the $\rho(T)$ behavior can be ascribed to a change in electronic energy spectrum near the Fermi level. The coefficients of the normal and anomalous Hall effect were determined. It was shown that the latter coefficient, $R_S$, is related to the residual resistivity $\rho_0$ by a power law $R_S \sim \rho_0^k/M_S$ with $M_S$ the spontaneous magnetization. The exponent $k$ was found to be 1.8 for Co$_2$FeZ alloys, which is typical for asymmetric scattering mechanisms, and 2.9 for Co$_2$YAl alloys, which indicates an additional contribution to the anomalous Hall effect. The temperature dependence of resistivity at low temperatures is analyzed and discussed in the framework of the two-magnon scattering theory.",1712.01584v1 2021-07-24,"Unravelling the phonon scattering mechanism in Half-Heusler alloys ZrCo1-xIrxSb (x = 0, 0.1, and 0.25)","Insight about the scattering mechanisms responsible for reduction in the lattice thermal conductivity (\k{appa}L) in Half-Heusler alloys (HHA) is imperative. In this context, we have thoroughly investigated the temperature response of thermal conductivity of ZrCo1-xIrxSb (x = 0, 0.1 and 0.25). For ZrCoSb, \k{appa}L is found to be ~15.13 W/m-K at 300 K, which is drastically reduced to ~4.37 W/m-K in ZrCo0.9Ir0.1Sb. This observed reduction is ascribed to softening of acoustic phonon modes and point defect scattering, on substitution of heavier mass. However, no further reduction in \k{appa}L is observed in ZrCo0.75Ir0.25Sb, because of identical scattering parameter. This has been elucidated based on the Klemens Callaway model. Also, in the parent alloy, phonon-phonon scattering mechanism plays a significant role in heat conduction process, whereas in Ir substituted alloys, point defect scattering (below 500 K) and phonon-phonon scattering (above 750 K) are the dominant scattering mechanisms. The minimum \k{appa}L is found to be ~1.73 W/m-K (at 950 K) in ZrCo0.9Ir0.1Sb, which is the lowest reported value till now, for n-type Zr based HHA. Our studies indicate that partial substitution of heavier mass element Ir at Co-site effectively reduces the \k{appa}L of n-type ZrCoSb, without modifying the nature of charge carriers.",2107.11567v1 2019-04-24,Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe2-xMnxCrAl,"We present a detailed study of structural, magnetic and thermodynamic properties of a series of Heusler alloys Fe2-xMnxCrAl (x=0, 0.25, 0.5, 0.75 and 1). Structural investigation of this series is carried out using high resolution synchrotron X-ray diffraction. Results suggest that with increasing Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC magnetization results show a decrement in paramagnetic (PM) to ferromagnetic (FM) phase transition temperature (TC) with increasing Mn concentration. From the systematic analysis of magnetic memory effect, heat capacity, time dependent magnetization, and DC field dependent AC susceptibility studies it is observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double CG-like transitions near Tf1~22 K, Tf2~4.2 K and Tf1~30.4 K, Tf2~9.5 K respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is noted at Tf2~11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long ranged magnetic ordering and this alloy undergoes three CG-like transitions at ~ 22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed analysis of temperature response of inverse DC susceptibility clearly reveals the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this phase persists with Mn concentration with a decrement in T*.",1904.10648v2 2018-08-07,Theoretical Investigation on the Effect of multinary Isoelectronic Substitution on TiCoSb based half-Heusler alloys,"To understand the effect of isoelectronic substitution on thermoelectric properties of TiCoSb based half - Heusler (HH) alloys, we have systematically studied the transport properties with substitution of Zr at Ti and Bi at Sb sites. The electronic structure of TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) and parent TiCoSb are investigated using the full potential linearized augmented plane wave method and the thermoelectric transport properties are calculated on the basis of semiclassical Boltzmann transport theory. The band analysis of the calculated band structures reveal that TixZr1-xCoSbxBi1-x has semiconducting behavior with indirect band gap at x = 0.25, 0.5 concentration and direct band gap behavior at x = 0.75 concentration. The TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) compounds show smaller band gap values as compared to the pure TiCoSb. The d electrons of Ti/Zr and Co dominate the electronic transport properties of TixZr1-xCoSbxBi1-x system. All these systems follow the empirical rule of 18 valence-electron content to bring semiconductivity in HH alloys. The isoelectronic substitution in TiCoSb can tune the band structure by shifting the Fermi level. This provides us lot of possibilities to get the desired band gap values for designing thermoelectrics with high efficiency. In this study we have showed that the isoelectronic substitution at both Ti and Sb site of TiCoSb has very small effect for increasing the ZT values and one should go for isoelectronic substitution at any one sites of TiCoSb HH alloys alone to improve ZT.",1808.02514v1 2018-04-15,$\mathrm{Co_2Fe_{1-x}Cr_xSi}$ Heusler Alloys : A promising material for spintronics application,"In this article, we investigated the effect of Cr substitution in place of Fe on the structural, magnetic and transport properties of $\mathrm{Co_2FeSi}$ alloy. A comprehensive structural analysis is done using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Quaternary Heusler compounds $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ with Cr content (x = 0.1, 0.3, 0.5) were found to crystallize in cubic structure. The synchrotron based EXAFS studies reveal that the anti-site disorder increases with the increase in Cr concentration. The saturation magnetization values in all the alloys are found to be less than those expected from the Slater-Pauling rule, which may be due to the some inherent disorder. A detailed resistivity analysis in the temperature range of 5-300 K is done, taking into account different scattering mechanisms. The residual resistivity ratio is found to decrease with increasing Cr concentration. A disorder induced resistivity minimum due to weak localization effect is seen for x = 0.5. The resistivity measurements also indicate that the half-metallic character survives upto 100 K for x = 0.1, whereas the alloys with x= 0.3 and 0.5 show signature of half- metallic nature even at higher temperatures. First principles calculation done with a more robust exchange correlation functional (namely HSE-06) confirms the half metallicity in the entire concentration range. Theoretically simulated band gap and magnetic moments compliment the experimental findings and are compared wherever possible. All these properties make $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ a promising material for spintronics application.",1804.05321v1 2019-08-21,Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi,"We report a combined theoretical and experimental investigation of half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi. Room temperature XRD analysis reveals that the alloy crystallizes in L21 disorder instead of pristine Y-type structure due to 50% swap disorder between the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal a net magnetization of 4 $\mu_B$ with Curie temperature of ~780 K. Resistivity measurement reveals the presence of localization effect below 35 K while above 100 K, a linear dependence is observed. Resistivity behavior indicates the absence of single magnon scattering, which indirectly supports the half-metallic nature. The majority spin band near the Fermi level clearly indicates the overlap of flat eg bands with sharply varying conduction bands that are responsible for the localization. In-depth analysis of the projected atomic d-orbital character of band structure reveals unusual bonding, giving rise to the flat eg bands purely arising out of Ru ions. Co-Ru swap disorder calculations indicate the robustness of half-metallic nature, even when the structure changes from Y-type to L21-type, with no major change in the net magnetization of the system. Thus, robust half-metallic nature, stable structure, and high Curie temperature make this alloy quite a promising candidate to be used as a source of highly spin-polarized currents in spintronic applications.",1908.07804v1 2021-07-31,Optical phonon modes assisted thermal conductivity in p-type ZrIrSb Half-Heusler alloy: A combined experimental and computational study,"Half Heusler (HH) alloys with 18 valence electron count have attracted significant interest in the area of research related to thermoelectrics. Understanding the novel transport properties exhibited by these systems with semiconducting ground state is an important focus area in this field. Large thermal conductivity shown by most of the HH alloy possesses a major hurdle in improving the figure of merit (ZT). Additionally, understanding the mechanism of thermal conduction in heavy constituents HH alloys is an interesting aspect. Here, we have investigated the high temperature thermoelectric properties of ZrIrSb through experimental studies, phonon dispersion and electronic band structure calculations. ZrIrSb is found to exhibit substantially lower magnitude of resistivity and Seebeck coefficient near room temperature, owing to existence of anti-site disorder between Ir/Sb and vacant sites. Interestingly, in ZrIrSb, lattice thermal conductivity is governed by coupling between the acoustic and low frequency optical phonon modes, which originates due to heavier Ir/Sb atoms. This coupling leads to an enhancement in the Umklapp processes due to the optical phonon excitations near zone boundary, resulting in a lower magnitude of \k{appa}L. Our studies point to the fact that the simultaneous existence of two heavy mass elements within a simple unit cell can substantially decrease the lattice degrees of freedom.",2108.00210v1 2023-04-11,Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy -- Microstructure and magnetic properties from powder to printed parts,"Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as magnetocaloric effect during the magneto-structural phase transition, making this material interesting for solid-state cooling application. Material processing by additive manufacturing can overcome difficulties related to machinability of the alloys, caused by their intrinsic brittleness. Since the magnetic properties and transition temperature are highly sensitive to the chemical composition, it is essential to understand and monitoring these properties over the entire processing chain. In the present work the microstructural and magnetic properties from gas-atomized powder to post-processed Ni-Mn-Sn alloy are investigated. Direct energy deposition was used for processing, promoting the evolution of a polycrystalline microstructure being characterized by elongated grains along the building direction. A complete and sharp martensitic transformation can be achieved after applying a subsequent heat treatment at 1173 K for 24 h. The Mn-evaporation of 1.3 at. % and the formation of Mn-oxide during DED-processing lead to an increase of the transition temperature of 45 K and a decrease of magnetization, clearly pointing at the necessity of controlling the composition, oxygen partial pressure and magnetic properties over the entire processing chain.",2304.05383v1 2023-09-20,Effects of disorder on the magnetic properties of the Heusler alloy V$_{2}$FeAl,"Magnetic properties of multicomponent alloys depend sensitively on the degree of atomic order on the different crystallographic sites. In this work we demonstrate the magnetic contrast between bulk and thin-film samples of the Heusler alloy V$_{2}$FeAl. Arc-melted bulk ingots show practically no site preference of the elements (A2 structure), whereas magnetron-sputtered thin-film samples display a higher degree of atomic ordering with a tendency towards XA-type order. Electronic structure calculations favour ferrimagnetic XA-type ordering, and the effect of different pairwise atomic disorder on the element specific and net magnetic moments are evaluated to reproduce experimental observations. XA-type thin-films with iron moment of 1.24 $\mu_{\mathrm{B}}$ determined by X-ray magnetic circular dichroism are in agreement with calculation, but the measured net moment of 1.0 $\mu_{\mathrm{B}}$ per formula unit and average vanadium moment are smaller than expected from calculations. The measured Curie temperature is approximately 500 K. Films with a higher degree of disorder have a T$_{\mathrm{C}}$ close to 300 K with a net moment of 0.1 $\mu_{\mathrm{B}}$ at low temperature. The large calculated vanadium moments are destroyed by partial disorder on $4d$ vanadium sites. By contrast, the arc-melted and annealed bulk alloy with a fully-disordered A2 structure shows no spontaneous magnetization; it is a Pauli paramagnet with dimensionless susceptibility $\chi_{\mathrm{v}}=-2.95\times10^{-4}$.",2309.11480v1 2022-05-28,Helicity-independent all-optical switching of magnetization in ferrimagnetic alloys,"We review and discuss the process of single-shot helicity-independent all-optical switching of magnetization by which a single suitably-ultrafast excitation, under the right conditions, toggles magnetization from one stable state to another. For almost a decade, this phenomenon was only consistently observed in specific rare-earth-transition-metal ferrimagnetic alloys of GdFeCo, but breakthrough experiments in recent years have revealed that the same behavior can be achieved in a wide range of multi-sublattice magnets including TbCo alloys doped with minute amounts of Gd, Gd/Co and Tb/Co synthetic ferrimagnets, and the rare-earth-free Heusler alloy Mn$_2$Ru$_x$Ga. Aiming to resolve the conditions that allow switching, a series of experiments have shown that the process in the ferrimagnetic alloys GdFeCo and Mn$_2$Ru$_x$Ga is highly sensitive to the pulse duration, starting temperature and the alloy composition. We argue here that the switching displayed by these two very different ferrimagnetic alloys can be generally understood within a single phenomenological framework describing the flow of angular momentum between the constituent sublattices and from the sublattices to the environment. The conditions that facilitate switching stem from the properties of these channels of angular momentum flow in combination with the size of the angular momentum reservoirs. We conclude with providing an outlook in this vibrant research field, with emphasis on the outstanding open questions pertaining to the underlying physics along with noting the advances in exploiting this switching process in technological applications.",2205.14342v1 2013-07-08,"Significant ZT Enhancement in p-type Ti(Co,Fe)Sb-InSb Nanocomposites via a Synergistic High Mobility Electron Injection Energy filtering and Boundary Scattering Approach","It has been demonstrated that InSb nanoinclusions, which are formed in situ, can simultaneously improve all three individual thermoelectric properties of the n-type half Heusler compound (Ti,Zr,Hf)(Co,Ni)Sb [Xie et al., Acta Mater. 58, 4795 (2010)]. In the work presented herein, we have adopted the same approach to the p-type half Heusler compound Ti(Co,Fe)Sb. The results of resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient measurements indicate that the combined high mobility electron injection, low energy electron filtering, and boundary scattering, again, lead to a simultaneous improvement of all three individual thermoelectric properties: enhanced Seebeck coefficient and electrical conductivity as well as reduced lattice thermal conductivity. A figure of merit of ZT=0.33 was attained at 900 K for the sample containing 1 atomic percent InSb nanoinclusions, a 450 percent improvement over the nanoinclusion-free sample. This represents a rare case that the same nanostructuring approach successfully works for both p-type and n-type thermoelectric materials of the same class, hence pointing to a promising materials design route for higher performance half-Heusler materials in the future and hopefully will realize similar improvement in TE devices based on such half Heusler alloys.",1307.2160v1 2015-05-14,"First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors","Employing first principles electronic structure calculations in conjunction with the frozen-magnon method we calculate exchange interactions, spin-wave dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin gapless semiconductor (SGS) compounds Mn$_2$CoAl, Ti$_2$MnAl, Cr$_2$ZnSi, Ti$_2$CoSi and Ti$_2$VAs. We find that their magnetic behavior is similar to the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice exchange interactions play an essential role in the formation of the magnetic ground state and in determining the Curie temperature, $T_\mathrm{c}$. All compounds, except Ti$_2$CoSi possess a ferrimagnetic ground state. Due to the finite energy gap in one spin channel, the exchange interactions decay sharply with the distance, and hence magnetism of these SGSs can be described considering only nearest and next-nearest neighbor exchange interactions. The calculated spin-wave dispersion curves are typical for ferrimagnets and ferromagnets. The spin-wave stiffness constants turn out to be larger than those of the elementary 3$d$-ferromagnets. Calculated exchange parameters are used as input to determine the temperature dependence of the magnetization and $T_\mathrm{c}$ of the SGSs. We find that the $T_\mathrm{c}$ of all compounds is much above the room temperature. The calculated magnetization curve for Mn$_2$CoAl as well as the Curie temperature are in very good agreement with available experimental data. The present study is expected to pave the way for a deeper understanding of the magnetic properties of the inverse-Heusler-based SGSs and enhance the interest in these materials for application in spintronic and magnetoelectronic devices.",1505.03632v1 2015-12-15,"Half-metallic, Co-based quaternary Heuslers for spintronics: defect- and pressure-induced transitions and properties","Heusler compounds offer potential as spintronic devices due to their spin-polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin-polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin-polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler ($L$2$_{1}$) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range. Antisite disorder between Co-Al pairs in CoMnCrAl and Co-Ge pairs in CoFeCrGe is energetically the most favored, and retain half-metallic character in Co-excess samples. However, Co-deficient samples undergo a transition from half-metallic to metallic, with a discontinuity in the saturation magnetization. For binary swaps, configurations that compete with the ground state are identified and show no loss of half-metallicity; however, the minority-spin bandgap and magnetic moments vary depending on the atoms swapped. For single binary swaps, there is a significant energy cost in CoMnCrAl but with no loss of half metallicity. Although a few configurations in CoFeCrGe energetically compete with the ground statei, however the minority-spin bandgap and magnetic moments vary depending on the atoms swapped. These informations should help in controlling these potential spintronic materials.",1512.04805v2 2018-03-05,Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds,"Newly emerged materials from the family of Heuslers and complex oxides exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much higher than even room temperature. In this work, using the semiclassical top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that utilizes such ferromagnetic semiconductors as channel materials, in addition to ferromagnetic source/drain contacts. Such a device could retain the spin polarization of injected electrons in the channel, the loss of which limits the operation of traditional spin transistors with non-ferromagnetic channels. We examine the operation of four material systems that are currently considered some of the most prominent known ferromagnetic semiconductors, three Heusler-type alloys (Mn2CoAl, CrVZrAl, CoVZrAl) and one from the oxide family (NiFe2O4). We describe their bandstructures by using data from DFT calculations. We investigate under which conditions high spin polarization and significant ION/IOFF ratio, two essential requirements for the spin-MOSFET operation, are both achieved. We show that these particular Heusler channels, in their bulk form, do not have adequate bandgap to provide high ION/IOFF ratios, and have small magnetoconductance compared to state-of-the-art devices. However, with confinement into ultra-narrow sizes down to a few nanometers, and by engineering their spin dependent contact resistances, they could prove promising channel materials for the realization of spin-MOSFET transistor devices that offer combined logic and memory functionalities. Although the main compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4 alone, we expect that the insight we provide is relevant to other classes of such materials as well.",1803.01789v1 2021-02-22,"Structural, magnetic, and magnetocaloric properties of Fe2CoAl Heusler nanoalloy","Spherical nanoparticles (NPs) of size 14 nm, made of intermetallic Fe2CoAl (FCA) Heusler alloy, are synthesized via the co-precipitation and thermal deoxidization method. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns confirm that the present nanoalloy is crystallized in A2-disordered cubic Heusler structure. Magnetic field (H) and temperature (T) dependent magnetization (M) results reveal that the NPs are soft ferromagnetic (FM) with high saturation magnetization (Ms) and Curie temperature (Tc). Fe2CoAl nanoalloy does not follow the Slater Pauling (SP) rule, possibly because of the disorder present in the system. We also investigate its magnetic phase transition (MPT) and magnetocaloric (MC) properties. The peak value of the magnetic entropy change vs T curve at a magnetic field change of 20 kOe corresponds to about 2.65 J/kg-K, and the observed value of refrigeration capacity (RCP) is as large as 44 J/kg, suggesting a large heat conversion in magnetic refrigeration cycle. The Arrott plot and the nature of the universal curve accomplish that the FM to paramagnetic (PM) phase transition in Fe2CoAl nanoalloy is of second-order. The present study suggests that the Fe2CoAl nanoscale system is proficient, useful and a good candidate for the spintronics application and opens up a window for further research on full-Heusler based magnetic refrigerants.",2102.11195v2 1999-11-25,Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation,"The results of fluorescence measurements of magnetic circular dichroism (MCD) in Mn L_2,L_3 X-ray emission and absorption for Heusler alloys NiMnSb and Co2MnSb are presented. Very intense resonance Mn L_3 emission is found at the Mn 2p_3/2 threshold and is attributed to a peculiarity of the threshold excitation in materials with the half-metallic character of the electronic structure. A theoretical model for the description of resonance scattering of polarized x-rays is suggested.",9911415v1 2002-03-04,X-ray spectra of 3d metals of Heusler alloys and La$_{1-x}$Sm$_x$Mn$_2$Si$_2$ compounds,"The Mn x-ray emission spectra and x-ray photoemission spectra of Mn-based Heusler alloys Co$_2$MnAl, Co$_2$MnSb and La$_{1-x}$Sm$_x$Mn$_2$Si$_2$ compounds (x=0, 0.8) have been measured and discussed in connection with a value local magnetic moment at Mn site. The spectra peculiarities reflect also the localization degree of 3d valence electrons of 3d metals in considered compounds.",0203069v3 2002-03-26,Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys,"We study the origin of the gap and the role of chemical composition in the half-ferromagnetic Heusler alloys using the full-potential screened KKR method. In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap. Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are semiconductors, but when Z_t > 18 antibonding states are also populated, thus the paramagnetic phase becomes unstable and the half-ferromagnetic one is stabilized. The minority occupied bands accommodate a total of nine electrons and the total magnetic moment per unit cell in mu_B is just the difference between Z_t and $2 \times 9$. While the substitution of the transition metal atoms may preserve the half-ferromagnetic character, substituting the $sp$ atom results in a practically rigid shift of the bands and the loss of half-metallicity. Finally we show that expanding or contracting the lattice parameter by 2% preserves the minority-spin gap.",0203534v3 2004-04-07,"First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb)","The interatomic exchange interactions and Curie temperatures in Ni-based full Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework of the density-functional theory. The calculation of the exchange parameters is based on the frozen-magnon approach. Despite closeness of the experimental Curie temperatures for all four systems their magnetism appeared to differ strongly. This difference involves both the Mn-Mn and Mn-Ni exchange interactions. The Curie temperatures, Tc, are calculated within the mean-field approximation by solving a matrix equation for a multi-sublattice system. Good agreement with experiment for all four systems is obtained. The role of different exchange interactions in the formation of Tc of the systems is discussed.",0404162v1 2004-10-28,Spin injection from the Heusler alloy Co_2MnGe into Al_0.1Ga_0.9As/GaAs heterostructures,"Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co_2MnGe decays more rapidly with increasing temperature.",0410751v1 2005-04-26,Pressure dependence of the Curie temperature in Ni2MnSn Heusler alloy: A first-principles study,"The pressure dependence of electronic structure, exchange interactions and Curie temperature in ferromagnetic Heusler alloy Ni2MnSn has been studied theoretically within the framework of the density-functional theory. The calculation of the exchange parameters is based on the frozen--magnon approach. The Curie temperature, Tc, is calculated within the mean-field approximation by solving the matrix equation for a multi-sublattice system. In agrement with experiment the Curie temperature increased from 362K at ambient pressure to 396 at 12 GPa. Extending the variation of the lattice parameter beyond the range studied experimentally we obtained non-monotonous pressure dependence of the Curie temperature and metamagnetic transition. We relate the theoretical dependence of Tc on the lattice constant to the corresponding dependence predicted by the empirical interaction curve. The Mn-Ni atomic interchange observed experimentally is simulated to study its influence on the Curie temperature.",0504644v1 2005-04-26,"First-principles study of exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge)","We report the parameter-free, density functional theory calculations of interatomic exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge). To calculate the interatomic exchange interactions we employ the frozen-magnon approach. The Curie temperatures are calculated within the mean-field approximation to the classical Heisenberg Hamiltonian by solving a matrix equation for a multi-sublattice system. Our calculations show that, although a large magnetic moment is carried by Mn atoms, competing ferromagnetic (inter sublattice) and antiferromagnetic (intra sublattice) Mn-Mn interactions in Mn2VAl almost cancel each other in the mean-field experienced by the Mn atoms. In Mn2VGe the leading Mn-Mn exchange interaction is antiferromagnetic. In both compounds the ferromagnetism of the Mn subsystem is favored by strong antiferromagnetic Mn-V interactions. The obtained value of the Curie temperature of Mn2VAl is in good agrement with experiment. For Mn2VGe there is no experimental information available and our calculation is a prediction.",0504679v1 2005-06-06,Unusual transport properties of ferromagnetic Heusler alloy Co$_2$TiSn,"We report results of magnetization, zero field resistivity and magnetoresistance measurements in ferromagnetic Heusler alloy Co$_2$TiSn. There is a striking change in the character of electron transport as the system undergoes the paramagnetic to ferromagnetic transition. In the paramagnetic state the nature of the electron transport is like that of a semiconductor and this changes abruptly to metallic behaviour at the onset of ferromagnetic ordering. Application of external magnetic field tends to suppress this semiconducting like transport leading to a negative magnetoresistance which reaches a peak in the vicinity of Curie temperature. Comparison is made with the similar unusual behaviour observed in other systems including UNiSn and manganites.",0506126v1 2006-01-17,Electron Correlations and the Minority-Spin Band Gap in Half-Metallic Heusler Alloys,"Electron-electron correlations affect the band gap of half-metallic ferromagnets by introducing non-quasiparticle states just above the Fermi level. In contrast to the spin-orbit coupling, a large asymmetric non-quasiparticle spectral weight is present in the minority-spin channel, leading to a peculiar finite-temperature spin depolarization effects. Using recently developed first-principle dynamical mean field theory, we investigate these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We discuss depolarization effects in terms of strength of local Coulomb interaction $U$ and temperature in FeMnSb. We propose Ni$_{1-x}$Fe$_{x}$MnSb alloys as a perspective materials to be used in spin-valve structures and for experimental search of non-quasiparticle states in half-metallic materials.",0601376v1 2006-05-31,Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films,"We have studied the possibly half metallic Co2FeSi full Heusler alloy by means of spin- and time-resolved photoemission spectroscopy. For excitation, the second and fourth harmonic of femtosecond Ti:sapphire lasers were used, with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the dependence of the measured surface spin polarization on the particular photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon photoemission (2PPE). The observed differences in the spin polarization can be explained by a spin-dependent lifetime effect occurring in the 2-photon absorption process. The difference in escape depth of the two methods in this context suggests that the observed reduction of spin polarization (compared to the bulk) cannot be attributed just to the outermost surface layer but takes place at least 4-6 nm away from the surface.",0606006v1 2006-08-31,Magnetic phase diagram of the semi-Heusler alloys from first-principles,"The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined at T=0 using first-principles calculations in conjunction with the frozen-magnon approximation. We show that the magnetism in these systems strongly depends on the number of conduction electrons, their spin polarization and the position of the unoccupied Mn 3d states with respect to Fermi energy. Various magnetic phases are obtained depending on these characteristics. The conditions leading to diverse magnetic behavior are identified. We find that in the case of a large conduction electron spin polarization and the unoccupied Mn 3d states lying far above the Fermi level, an RKKY-like ferromagnetic interaction is dominating. On the other hand, the antiferromagnetic superexchange becomes important in the presence of large peaks of the unoccupied Mn 3d states lying close to the Fermi energy. The overall magnetic behavior depends on the competition of these two exchange mechanisms. The obtained results are in very good agreement with the available experimental data.",0609001v1 2007-01-25,Doping of Mn$_2$VAl and Mn$_2$VSi Heusler alloys as a route to half-metallic antiferromagnetism,"Half-metallic antiferromagnets are the ideal materials for spintronic applications since their zero magnetization leads to lower stray fields and thus tiny energy losses. Starting from the Mn$_2$VAl and Mn$_2$VSi alloys we substitute Co or Fe for Mn and we show by means of first-principle electronic structure calculations that the resulting compounds are ferrimagnets. When the total number of valence electrons reaches the magic number of 24 the Fe-doped compounds are semi-metals and thus non-magnetic while the Co-doped ones show the desirable half-metallic antiferromagnetic character. The compounds are very likely to be synthesized experimentally since the parent compounds, Mn$_2$VAl and Co$_2$VAl, have been already grown in the Heusler $L2_1$ lattice structure.",0701611v1 2008-01-13,3d-electron induced magnetic phase transition in half-metallic semi-Heusler alloys,"We study the effect of the non-magnetic 3\textit{d} atoms on the magnetic properties of the half-metallic (HM) semi-Heusler alloys Co$_{1-x}$Cu$_{x}$MnSb and Ni$_{1-x}$Cu$_{x}$MnSb ($0 \leq x \leq 1$) using first-principles calculations. We determine the magnetic phase diagram of both systems at zero temperature and obtain a phase transition from a ferromagnetic to an antiferromagnetic state. For low Cu concentrations the ferromagnetic RKKY-like exchange mechanism is dominating, while the antiferromagnetic superexchange coupling becomes important for larger Cu content leading to the observed magnetic phase transition. A strong dependence of the magnetism in both systems on the position of the Fermi level within the HM gap is obtained. Obtained results are in good agreement with the available experimental data.",0801.1968v1 2008-01-15,"Structural and magnetic properties of half-heusler alloys NiCrZ (Z = Si, P, Ge, As, Te): First principle study","We present a first principle study of new class of high-$T_c$ half-heusler ferromagnets NiCrZ (Z = Si, P, Ge, As, Te). The structure and magnetic properties are investigated through the calculation of the electronic structure, equilibrium lattice constant, magnetic exchange interaction $J_{ij}$ and Curie temperature $T_c$. The role of $sp$-elements and the influence of lattice expansion/compression are also studied. In alloys having 20 valence electrons, a pseudo-gap of the majority band can be formed at Fermi level. Otherwise, the half-metallicity and ferromagnetism at temperatures much higher than room temperature are found to be stable in a wide range of lattice expansion. Based on these results, NiCrZ can be expected to be promising materials for spintronics.",0801.2222v1 2008-01-15,"New High-$T_c$ Half-Heusler Ferromagnets NiMnZ (Z = Si, P, Ge, As)","Based on the first principle calculation, we propose a new class of high-$T_c$ half-heusler ferromagnets NiMnZ (Z = Si, P, Ge, As). The structural and magnetic properties are investigated through the calculation of the electronic structure, phase stability, equilibrium lattice constant, magnetic exchange interaction $J_{ij}$ and Curie temperature $T_c$. It is found that all alloys show half-metallicity and ferromagnetism at temperatures much higher than room temperature in a wide range of lattice expansion (compression). At the equilibrium lattice constant, $T_c$ of 715K, 840K, 875K and 1050K are predicted by Monte Carlo simulation for NiMnP, NiMnAs, NiMnGe and NiMnSi, respectively. Following these results, these alloys are strongly expected to be promising candidates for spintronic applications.",0801.2225v1 2008-11-20,Current-perpendicular-to-plane giant magnetoresistance of a spin valve using Co2MnSi Heusler alloy electrodes,"We report the current-perpendicular-to-plane giant magnetoresistance of a spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu spacer layer despite the large lattice mismatch between Cu and CMS. The highest MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room temperature and 6 K, respectively. The high spin polarization of the epitaxial CMS layers is the most likely origin of the high MR ratio.",0811.3282v1 2009-05-24,Density functional study of elastic and vibrational properties of the Heusler-type alloys Fe$_2$VAl and Fe$_2$VGa,"The structural and elastic properties as well as phonon-dispersion relations of the Heusler-type alloys Fe$_2$VAl and Fe$_2$VGa are computed using density-functional and density-functional perturbation theory within the generalized-gradient approximation. The calculated equilibrium lattice constants agree well with the experimental values. The elastic constants of Fe$_2$VAl and Fe$_2$VGa are predicted for the first time. From the elastic constants the shear modulus, Young's modulus, Poisson's ratio, sound velocities and Debye temperatures are obtained. By analyzing the ratio between the bulk and shear modulii, we conclude that both Fe$_2$VAl and Fe$_2$VGa are brittle in nature. The computed phonon-dispersion relation shows that both compounds are dynamically stable in the L1$_2$ structure without any imaginary phonon frequencies. The isomer shifts of Fe in the two compounds are discussed in terms of the Fe s partial density of states, which reveal larger ionicity/less hybridization in Fe$_2$VGa than in Fe$_2$VAl. For the same reason the Cauchy pressure is negative in Fe$_2$VAl but positive in Fe$_2$VGa",0905.3909v1 2010-06-01,Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy,"The effect of pressure on the magnetic and the magnetocaloric properties around the martensitic transformation temperature in NiCoMnSb Heusler alloy has been studied. The martensitic transition temperature has significantly shifted to higher temperatures with pressure, whereas the trend is opposite with the application of applied magnetic field. The maximum magnetic entropy change around the martensitic transition temperature for Ni45Co5Mn38Sb12 is 41.4 J/kg K at the ambient pressure, whereas it is 33 J/kg K at 8.5 kbar. We find that by adjusting the Co concentration and applying suitable pressure, NiCoMnSb system can be tuned to achieve giant magnetocaloric effect spread over a large temperature span around the room temperature, thereby making it a potential magnetic refrigerant material for applications.",1006.0067v1 2010-06-01,Giant inverse magnetocaloric effect near room temperature in Co substituted NiMnSb Heusler alloys,"The effect of Co on the structural, magnetic and magnetocaloric effect (MCE) of Ni50-xCoxMn38Sb12 (x=0,2,3,4,5) Heusler alloys was studied. Using x-ray diffraction, we show the evolution of the martensitic phase from the austenite phase. The martensitic transition temperature is found to decrease monotonically with Co concentration. Remarkable enhancement of MCE is observed near room temperature upon Co substitution. The maximum magnetic entropy change of 34 Jkg-1K-1 was achieved in x=5 at 262 K in a field of 50 kOe and a value of 29 Jkg-1K-1 found near room temperature. The significant increase in the magnetization associated with the reverse martensitic transition is responsible for the giant MCE in these compounds.",1006.0072v1 2010-10-15,"Direct measurements of the magnetocaloric effect in ribbon samples of Heusler alloys Ni - Mn - M (M = In, Sn)","Direct measurements of the magnetocaloric effect in samples of rapidly quenched ribbons of Mn50Ni40In10 and Ni50Mn37Sn13 Heusler alloys, with potential applications in magnetic refrigeration technology, are carried out. The measurements were made by a precise method based on the measurement of the oscillation amplitude of the temperature in the sample while is subjected to a modulated magnetic field. In the studied compositions both direct and inverse magnetocaloric effects associated with magnetic (paramagnet - ferromagnet - antiferromagnet) and structural (austenite - martensite) phase transitions are found. Additional inverse magnetocaloric effects of small value are observed around the ferromagnetic transitions.",1010.3135v1 2010-12-09,Epitaxial germanidation of full-Heusler Co2FeGe alloy thin films formed by rapid thermal annealing,"The authors demonstrated that a full-Heusler Co2FeGe (CFG) alloy thin film was epitaxially grown by rapid-thermal-annealing-induced germanidation of an Fe/Co/pseudo-Ge(001)-on-insulator (GOI) multilayer formed on a Si-on-insulator (SOI) substrate. X-ray diffraction (XRD) measurements with the out-of-plane and in-plane configurations revealed that the CFG film was epitaxially grown along the [001] direction with the in-plane epitaxial relation of CFG[100]||GOI[100], although the film slightly contained a texture component. The strong (111) and (200) superlattice diffraction intensities indicated that the CFG film had a high degree of order for the L21 structure. Cross-sectional high-resolution transmission electron microscopy images of the film implied that the film had the dominant epitaxial and slight texture components, which was consistent with the XRD measurements. The epitaxial component was grown directly on the BOX layer of the SOI substrate without the formation of any interfacial layer.",1012.1917v1 2010-12-13,Effect of Si and Ga substitutions on the magnetocaloric properties of NiCoMnSb quaternary Heusler alloys,"The effect of Si and Ga substitutions on the magnetic and the magnetocaloric properties in Heusler based system Ni46Co4Mn38Sb12-xZx (Z=Si and Ga) has been studied. From the M(T) plots it is found that Si substitution stabilizes the austenite phase, whereas, Ga substitution stabilizes the martensite phase. Strong metamagnetic behaviour is observed in the M(H) isotherms for Si=0.75 and 1, whereas, such a behaviour is absent in the Ga substituted alloys. Associated with magneto-structural transition, large MCE of 58 J/kg K and 70 J/kg K is observed for x=0.75 and 1, respectively in the case of Si. Though the MCE observed in x=0.5 and 1 in the case of Ga is much lower, the MCE peak is found to be quite broad.",1012.2684v1 2011-11-19,Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars,"We have studied microwave emission from a current-perpendicular-to-plane pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes. Large emission amplitude exceeding 150 nV/Hz^0.5, partly owing to the large magnetoresistance, and narrow generation linewidth below 10 MHz are observed. We also find that the linewidth shows significant dependence on the applied field magnitude and its angle within the film plane. A minimum in the linewidth is observed when the slope of the frequency versus current becomes near zero. This agrees with theoretical prediction that takes into account non-linear phase noise as a source for linewidth broadening.",1111.4539v1 2012-10-22,"Thickness-dependent structural, magnetic and transport properties of epitaxial Co2FeAl Heusler alloy thin films","We report on a systematic study of the structural, magnetic properties and the anomalous Hall effect, in the Heusler alloy Co2FeAl (CFA) epitaxial films on MgO(001), as a function of film thickness. It was found that the epitaxial CFA films show a highly ordered B2 structure with an in-plane uniaxial magnetic anisotropy. An analysis of the electrical transport properties reveals that the lattice and magnon scattering contributions to the longitudinal resistivity. Independent on the thickness of films, the anomalous Hall resistivity of CFA films is found to be dominated by skew scattering only. Moreover, the anomalous Hall resistivity shows weakly temperature dependent behavior, and its absolute value increases as the thickness decreases. We attribute this temperature insensitivity in the anomalous Hall resistivity to the weak temperature dependent of tunneling spin-polarization in the CFA films, while the thickness dependence behavior is likely due to the increasing significance of interface or free surface electronic states.",1210.5807v1 2013-11-28,Local magnetism and structural properties of Heusler Ni$_2$MnGa alloys,"We present a detailed experimental study of bulk and powder samples of the Heusler shape memory alloy Ni$_2$MnGa, including zero-field static and dynamic $^{55}$Mn NMR experiments, X-ray powder diffraction and magnetization experiments. The NMR spectra give direct access to the sequence of structural phase transitions in this compound, from the high-T austenitic phase down to the low-T martensitic phase. In addition, a detailed investigation of the so-called rf-enhancement factor provides local information for the magnetic stiffness and restoring fields for each separate coordination, structural, crystallographic environment, thus differentiating signals coming from austenitic and martensitic components. The temperature evolution of the NMR spectra and the rf-enhancement factors shows strong dependence on sample preparation. In particular, we find that sample powderization gives rise to a significant portion of martensitic traces inside the high-T austenitic region, and that these traces can be subsequently removed by annealing.",1311.7414v1 2015-05-12,Examining the thermal conductivity of half-Heusler alloy TiNiSn by first-principles calculations,"The thermoelectric properties of half-Heusler alloy TiNiSn have been studied for decade, however, theoretical report on its thermal conductivity is still little known, because it is difficult to estimate effectively the lattice thermal conductivity. In this work, we use the ShengBTE code developed recently to examine the lattice thermal conductivity of TiNiSn. The calculated lattice thermal conductivity at room temperature is 7.6 W/mK, which is close to the experimental value of 8 W/mK. We also find that the total and lattice thermal conductivities dependent temperature are in good agreement with available experiments, and the total thermal conductivity is dominated by the lattice contribution. The present work is useful for the theoretical prediction of lattice thermal conductivity and the optimization of thermoelectric performance.",1505.02845v1 2015-05-28,Large ground state magnetic moment and magnetocaloric effect in Ni2Mn1.4In0.6,"A large conventional magnetocaloric effect at the second order magnetic transition in cubic Ni2Mn1.4In0.6 Heusler alloy is reported. The isothermal magnetization at 2K shows a huge ground state magnetic moment of about 6.17 {\mu}B/f.u. The theoretical calculations show that the origin of the large magnetic moment in cubic Ni2Mn1.4In0.6 results from the strong ferromagnetic interaction between Mn- Ni and Mn-Mn sublattices. The experimental magnetic moment is in excellent agreement with the moment calculated from the theory. The large magnetic moment gives rise to considerably high adiabatic temperature and entropy changes at the magnetic transition. The present study opens up the possibility to explore cubic Heusler alloys for magnetocaloric applications.",1505.07677v2 2015-10-23,Resonant impurity states in chemically disordered half-Heusler Dirac semimetals,"We address the electron transport characteristics in bulk half-Heusler alloys with their compositions tuned to the borderline between topologically nontrivial semi-metallic and trivial semiconducting phases. The precise first-principles calculations based on the coherent potential approximation (CPA) reveal that all the studied systems exhibit sets of dispersionless impurity-like resonant levels, with one of them being located right at the Dirac point. By means of the Kubo formalism we reveal that the residual conductivity of these alloys is strongly suppressed by impurity scattering, whereas the spin Hall conductivity exhibits a large value which is comparable to that of Pt, thereby leading to divergent spin Hall angles.",1510.06935v1 2015-12-04,Suppression of the ferromagnetic order in the Heusler alloy Ni50Mn35In15 by hydrostatic pressure,"We report the effect of hydrostatic pressure on the magnetic and structural properties of the shape-memory Heusler alloy Ni50Mn35In15. Magnetization and x-ray diffraction experiments were performed at hydrostatic pressures up to 5 GPa using diamond anvil cells. Pressure stabilizes the martensitic phase, shifting the martensitic transition to higher temperatures and suppresses the ferromagnetic austenitic phase. Above ~3 GPa, where the martensitic-transition temperature approaches the Curie temperature in the austenite, the magnetization shows no indication of ferromagnetic ordering anymore. We further find an extremely large temperatureregion with a mixture of martensite and austenite phases, which directly relates to the magnetic properties.",1512.01407v1 2016-06-14,Defect-induced magnetic structure of CuMnSb,"Ab initio total energy calculations show that the antiferromagnetic (111) order is not the ground state for the ideal CuMnSb Heusler alloy in contrast to the results of neutron diffraction experiments. It is known, that Heusler alloys usually contain various defects depending on the sample preparation. We have therefore investigated magnetic phases of CuMnSb assuming the most common defects which exist in real experimental conditions. The full-potential supercell approach and a Heisenberg model approach using the coherent potential approximation are adopted. The results of the total energy supercell calculations indicate that defects that bring Mn atoms close together promote the antiferromagnetic (111) structure already for a low critical defect concentrations ($\approx$ 3%). A detailed study of exchange interactions between Mn-moments further supports the above stabilization mechanism. Finally, the stability of the antiferromagnetic (111) order is enhanced by inclusion of electron correlations in narrow Mn-bands. The present refinement structure analysis of neutron scattering experiment supports theoretical conclusions.",1606.04238v1 2016-09-29,"On the rich magnetic phase diagram of (Ni, Co)-Mn-Sn Heusler alloys","We put a spotlight on the exceptional magnetic properties of the metamagnetic Heusler alloy (Ni,Co)-Mn-Sn by means of first principles simulations. In the energy landscape we find a multitude of local minima, which belong to different ferrimagnetic states and are close in total magnetization and energy. All these magnetic states correspond to the local high spin state of the Mn atoms with different spin alignments and are related to the magnetic properties of Mn. Compared to pure Mn, the magneto-volume coupling is reduced by Ni, Co, and Sn atoms in the lattice and no local low-spin Mn states appear. For the cubic phase we find a ferromagnetic ground state whereas the global energy minimum is a tetragonal state with complicated spin structure and vanishing magnetization which so far has been overlooked in simulations.",1609.09399v1 2017-01-06,Modulations in martensitic Heusler alloys originate from nanotwin ordering,"Heusler alloys exhibiting magnetic and martensitic transitions enable applications like magnetocaloric refrigeration and actuation based on the magnetic shape memory effect. Their outstanding functional properties depend on low hysteresis losses and low actuation fields. These are only achieved if the atomic positions deviate from a tetragonal lattice by periodic displacements. The origin of the so-called modulated structures is the subject of much controversy: They are either explained by phonon softening or adaptive nanotwinning. Here we used large-scale density functional theory calculations on the Ni2MnGa prototype system to demonstrate interaction energy between twin boundaries. Minimizing the interaction energy resulted in the experimentally observed ordered modulations at the atomic scale, it explained that a/b twin boundaries are stacking faults at the mesoscale, and contributed substantially to the macroscopic hysteresis losses. Furthermore, we found that phonon softening paves the transformation path towards the nanotwinned martensite state. This unified both opposing concepts to explain modulated martensite.",1701.01562v2 2017-01-29,$d^0$-$d$ half-Heusler alloys: A class of future spintronic materials,"It is shown by rigorous ab initio calculations that half-Heusler alloys of transition metals and $d^0$ metals, defined by the valence electronic configuration $ns^{1,2},(n-1)d^0$, can produce all kinds of half-metallic behavior including the elusive Dirac half-semimetallicity that is reported for the first time in the real 3D material CoKSb. Together with the predicted magnetic and chemical stability, this paves the way for massless and dissipationless spintronics of the future. Furthermore, the introduction of $d^0$ atoms is shown to stabilize the otherwise instable chemical structure of zinc-blende transition metal pnictides and chalcogeneides without altering the $p$-$d$ exchange that is mainly responsible for their half-metallicity, therefore, making their application in spintronic devices feasible.",1701.08397v3 2017-07-17,Possible spin gapless semiconductor type behaviour in CoFeMnSi epitaxial thin films,"Spin-gapless semiconductors with their unique band structures have recently attracted much attention due to their interesting transport properties that can be utilized in spintronics applications. We have successfully deposited the thin films of quaternary spin-gapless semiconductor CoFeMnSi Heusler alloy on MgO (001) substrates using a pulsed laser deposition system. These films show epitaxial growth along (001) direction and display uniform and smooth crystalline surface. The magnetic properties reveal that the film is ferromagnetically soft along the in-plane direction and its Curie temperature is well above 400 K. The electrical conductivity of the film is low and exhibits a nearly temperature independent semiconducting behaviour. The estimated temperature coefficient of resistivity for the film is -7x10^-10 Ohm.m/K, which is comparable to the values reported for spin-gapless semiconductors.",1707.05078v2 2017-07-21,Mn$_2$VAl Heusler alloy thin films: Appearance of antiferromagnetism and an exchange bias in a layered structure with Fe,"Mn$_2$VAl Heusler alloy films were epitaxially grown on MgO(100) single crystal substrates by means of ultra-high-vacuum magnetron sputtering. A2 and L2$_1$ type Mn$_2$VAl order was controlled by the deposition temperatures. A2-type Mn$_2$VAl films showed no spontaneous magnetization and L2$_1$-type Mn$_2$VAl films showed ferrimagnetic behavior with a maximum saturation magnetization of 220 emu/cm$^3$ at room temperature. An antiferromagnetic reflection was observed with neutron diffraction at room temperature for an A2-type Mn$_2$VAl film deposited at 400$^\circ$C. A bilayer sample of the antiferromagnetic A2 Mn$_2$VAl and Fe showed an exchange bias of 120 Oe at 10 K.",1707.06731v1 2018-03-05,Measurement independent magnetocaloric effect in Mn-rich Mn-Fe-Ni-Sn(Sb/In) Heusler alloys,"We report a systematic study on the magneto-structural transition in Mn-rich Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence electron concentration (e/a ratio) fixed. The martensitic transition (MT) temperature is found to shift by following a proportional relationship with the e/a ratio of the magnetic elements alone. The magnetic entropy change across MT for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different measurement methods (isofield magnetization (M) vs temperature (T), isothermal M vs field (H) and heat capacity (HC) vs T). We observed that though the peak value of magnetic entropy change changes with the measurement methods, the broadened shape of the magnetic entropy change vs T curves and the corresponding cooling power (~140 Jkg-1) remains invariant. The equivalent adiabatic temperature change ~ -2.6 K has been obtained from indirect measurements of temperature change. Moreover, an exchange bias field ~ 783 Oe at 5 K and a magnetoresistance of -30% are also obtained in one of these materials.",1803.01566v3 2018-11-15,"LnPd$_{2}$Sn (Ln=Sc, Y, Lu) class of Heusler alloys for topological superconductivity","Based on the first-principles electronic structure calculations and the symmetry analysis, we predict that the topological superconductivity may occur on the surface of the LnPd$_{2}$Sn (Ln=Sc, Y, Lu) class of Heusler alloys. The calculated electronic band structure and topological invariant demonstrate that the LnPd$_{2}$Sn family is topologically nontrivial. The further slab calculations show that the nontrivial topological surface states of LnPd$_{2}$Sn exist within the bulk band gap and meanwhile they cross the Fermi level. Considering that the LnPd$_{2}$Sn class of compounds were all found experimentally to be superconducting at low temperature, the surface topological superconductivity is likely to be generated via the proximity effect. Thus the LnPd$_{2}$Sn class of compounds shall be a promising platform for exploring novel topological superconductivity and handling Majorana zero modes.",1811.06401v1 2019-11-06,High spin mixing conductance and spin interface transparency at $Co_2Fe_{0.4}Mn_{0.6}Si$ Heusler alloy and Pt interface,"Ferromagnetic materials exhibiting low magnetic damping ($\alpha$) and moderately high saturation magnetization are required from the viewpoints of generation, transmission and detection of spin wave. Since spin-to-charge conversion efficiency is another important parameter, high spin mixing conductance ($g_{r}^{\uparrow \downarrow}$) is the key for efficient spin-to-charge conversion. Full Heusler alloys e.g. $Co_2Fe_{0.4}Mn_{0.6}Si$ (CFMS), which are predicted to be 100$\%$ spin polarized, possess low $\alpha$. However, the $g_{r}^{\uparrow \downarrow}$ at the interface between CFMS and a paramagnet has not fully been understood. Here, we report the investigations of spin pumping and inverse spin Hall effect in $CFMS/Pt$ bilayers. Damping analysis indicates the presence of significant spin pumping at the interface of CFMS and Pt, which is also confirmed by the detection of inverse spin Hall voltage. We show that in CFMS/Pt the $g_{r}^{\uparrow \downarrow}$ (1.77$\times$10$^{20}$m$^{-2}$) and interface transparency (84$\%$) are higher compared to values reported for other ferromagnet/heavy metal systems.",1911.02230v1 2019-04-04,\textit{Ab initio} study of Bi-based half Heusler alloys as potential thermoelectric prospects,"We investigated six heavy element bismuth-based 18-VEC half-Heusler alloys CoTiBi, CoZrBi, CoHfBi, FeVBi, FeNbBi, and FeTaBi by first principles approach, in search of better thermoelectric prospects. The motivation is driven by expected lower thermal conductivity and the recent discovery of CoZrBi-based materials. Significantly, our calculated power factor values of all the systems show an increment of $\sim$40\% in comparison to the reported \textit{p}-type CoTiSb. We propose that doping at Bi-site, on account of electronic features, will be helpful in achieving the proposed power factor values. Interestingly, the thermal conductivity of CoTiBi and CoZrBi was found to be lower and that of CoHfBi was almost parallel, in comparison to the reported CoTiSb. We also provide conservative estimates of the figure of merit, exceeding the reported CoTiSb and comparable to FeNbSb. Overall, our results suggest potential new candidates of bismuth-based ternary compounds for high thermoelectric performance.",1904.02488v1 2012-09-12,Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements,"We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following magnetic saturation, the dominant magnetic states consist of quasi-uniform configurations, where a strong influence from the magnetocrystalline anisotropy is visible. Heating experiments show the stability of the spin configuration of domain walls in confined geometries up to 800 K. The switching temperature for the transition from transverse to vortex walls in ring elements is found to increase with ring width, an effect attributed to structural changes and consequent changes in magnetic anisotropy, which start to occur in the narrower elements at lower temperatures.",1209.2702v1 2014-06-13,"Investigation of the electronic and thermoelectric properties of Fe2 ScX (X = P, As and Sb) full Heusler alloys by using first principles calculations","By using ab initio electronic structure calculations here we report the three new full Heusler alloys which are possessing very good thermoelectric behavior and expected to be synthesized in the laboratories. These are Fe2 ScP, Fe2 ScAs and Fe2 ScSb compound. First two compounds are indirect band gap semiconductors and the last one shows semimetallic ground state. The value of band gap of Fe2 ScP and Fe2 ScAs is 0.3 and 0.09 eV, respectively. These compounds show the presence of flat conduction bands along {\Gamma} - X-direction suggesting for the large electron like effective mass and promising for very good thermoelectric behavior of the compounds. At 200 K, the Seebeck coefficients of Fe2 ScP, Fe2 ScAs and Fe2 ScSb compounds are -770, -386 and -192{\mu}V/K, respectively. The maximum power factor (P F ) is expected for the n-type doping in these materials. The heavily doped Fe2 ScP and Fe2 ScAs have P F >60 for a wide temperature range, which is comparable to the PF of Bi2 Te3 - a well known and one of the best commercially used thermoelectric material. Present work suggests the possible thermoelectric applicability of these materials in a wide temperature range.",1406.3425v1 2019-02-05,Co-existence of spin semi-metallic and Weyl semi-metallic behavior in FeRhCrGe,"In this letter, we report the discovery of a new class of spintronic materials, namely spin semi-metals (SSM), employing both theoretical and experimental tools. The band structure of this class of materials is such that one of the spin bands resembles that of a semi-metal, while the other is similar to that of an insulator/semiconductor. This report is the experimental verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a magnetic moment 3 $\mu_B$ and a Curie temperature of 550 K. The measurement below 300 K shows nearly temperature independent conductivity and a relatively moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous first principles calculations. Band structure calculations also reveal that the spin up (semi metallic) band has combined features of type II Weyl and nodal line semimetal. As such, this study opens up the possibility of a new class of material with combined spintronic and topological properties, which is important both from fundamental and applied point of view.",1902.01593v2 2020-04-15,Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys,"Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large thermal hysteresis at their first-order martensitic phase transition which hinder a technological application in magnetic refrigeration. By optimizing the Cu content in Ni$_2$Cu$_x$Mn$_{1.4-x}$In$_{0.6}$, we obtained a thermal hysteresis of the martensitic phase transition in Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ of only 6 K. We can explain this very small hysteresis by an almost perfect habit plane at the interface of martensite and austenite phases. Application of hydrostatic pressure does not reduce the hysteresis further, but shifts the martensitic transition close to room temperature. The isothermal entropy change does not depend on warming or cooling protocols and is pressure independent. Experiments in pulsed-magnetic fields on Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ find a reversible magnetocaloric effect with a maximum adiabatic temperature change of -13 K.",2004.07145v1 2021-03-29,"Prediction of electronic and half metallic properties of Mn$_2$YSn (Y = Mo, Nb, Zr) Heusler alloys","We investigate the structural, electronic and magnetic properties of the full Heusler compounds Mn$_2$YSn (Y = Mo, Nb, Zr) by first-principles density functional theory using the generalized gradient approximation. It is found that the calculated lattice constants are in good agreement with the theoretical values. We observe that the Cu$_2$MnAl-type structure is more stable than the Hg$_2$CuTi type. The calculated total magnetic moments of Mn$_2$NbSn and Mn$_2$ZrSn are 1 $\mu_{\text{B}}$ and 2 $\mu_{\text{B}}$ at the equilibrium lattice constant of 6.18 \AA and 6.31 \AA, respectively, for the Cu$_2$MnAl-type structure. Mn$_2$MoSn have a metallic character in both Hg$_2$CuTi and Cu$_2$MnAl type structures. The total spin magnetic moment obeys the Slater-Pauling rule. Half-metal exhibits 100% spin polarization at the Fermi level. Thus, these alloys are promising magnetic candidates in spintronic devices.",2103.15542v1 2022-03-22,A strategic high throughput search for identifying stable Li based half Heusler alloys for spintronics applications,"In this work, high throughput DFT calculations are performed on the alkali metal-based half Heusler alloys; LiY$_p$Y$^\prime_{1-p}$S (Y, Y$^\prime$ = V, Cr, Mn, Fe, Co, Ni and $\mathit{p}$ = 0, 0.25, 0.5, 0.75, 1). Starting with 243 structural replica, systematic filters are designed to select the energetically and vibrationally favorable compositions by considering the contributions stemming from the magnetic alignments of the ions. Thereby, 26 dynamically stable magnetic compositions are identified, of which 10 are found to be ferromagnetic (FM), 4 antiferromagnetic (AFM) and 12 ferrimagnetic (FiM). 4 FM and 8 FiM ones are found to show 100 $\%$ spin polarization. Further, tetragonal distortion is found to be present in 4 FM, 3 FiM and 4 AFM compositions, which indicates the possibility of easy-axis magnetocrystalline anisotropy. The ferromagnetic LiFe$_{0.5}$Mn$_{0.5}$S and antiferromagnetic LiFeS are found to have the most prominent easy-axis magnetocrystalline anisotropy.",2203.11794v1 2022-03-22,"Lattice Dynamics, Mechanical Properties, Electronic Structure and Magnetic Properties of Equiatomic Quaternary Heusler Alloys CrTiCoZ (Z =Al,Si) using first principles calculations","First principles calculations are performed to investigate the thermodynamical stability, dynamical, mechanical, electronic and magnetic properties of CrTiCoZ (Z= Al/Si) novel quaternary Heusler alloys. Y-type III atomic configuration is found to be the most stable structure for both compounds. The melting temperatures of both compounds are as high as 2142 K and 2420 K for CrTiCoAl and CrTiCoSi, respectively. The electronic structure calculations using GGA-PBE approach show a half metallic behavior of CrTiCoAl. The spin-down channel exhibits a direct band gap of 0.15 eV, whereas the spin-up channel is metallic making CrTiCoAl a half metallic ferromagnet with 100% spin polarization and an appreciable magnetic moment of -2 Bohr Magnetons. The Curie temperature of CrTiCoAl is well above the room temperature (385K), whereas that of CrTiCoSi is below the room temperature (203K).",2203.11858v1 2022-03-23,Effective decoupling of ferromagnetic sublattices by frustration in Heusler alloys,"Magnetic frustration in ferromagnetic metallic systems is unusual due to the long-range and symmetric nature of the exchange interactions. In this work we prove that it is possible to obtain a highly frustrated ferromagnetic phase in a multi-sublattices cubic structure through a fine tuning of the magnetic interactions. This peculiar state is achieved in Ni-Mn-(In, Sn) Heusler alloys and results in the effective decoupling of their two intertwined ferromagnetic sublattices. One sublattice is ferromagnetic long range ordered below the macroscopic Curie temperature (TC ) whereas the second one remains disordered until a crossover to a polarized state occurs at T << TC . This result points out that a fine engineering of the magnetic interactions in metallic systems can lead to interesting novel and emergent phenomena.",2203.12498v2 2016-03-29,Revealing the nature of magnetic phases in the semi-Heusler alloy Cu0.85Ni0.15MnSb,"We report the magnetic, magnetocaloric, and magnetotransport properties of the semi-Heusler alloy Cu0.85Ni0.15MnSb, which exhibits coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) phases. A broad magnetic phase transition is evident from the temperature variations of magnetization, heat capacity, and isothermal magnetic entropy change. This is due to the presence of both AFM and FM phases at low temperatures. The variation of electrical resistivity with temperature shows three distinct regions of magnetic phases. The magnetoresistance (MR) results also show the presence of AFM and FM phases at temperatures below 45 K, and a FM phase at temperature above 45K. Though there is no signature of a spin-glass state at low temperatures, various results point towards the presence of short-range magnetic correlations at low temperatures.",1603.08618v1 2017-02-03,Field dependent neutron diffraction study in Ni50Mn38Sb12 Heusler alloy,"In this paper, we present temperature and field dependent neutron diffraction (ND) study to unravel the structural and the magnetic properties in Ni50Mn38Sb12 Heusler system. This alloy shows martensitic transition from high temperature austenite cubic phase to low temperature martensite orthorhombic phase on cooling. At 3 K, the lattice parameters and magnetic moments are found to be almost insensitive to field. Just below the martensitic transition temperature, the martensite phase fraction is found to be 85%. Upon applying the field, the austenite phase becomes dominant, and the field induced reverse martensitic transition is clearly observed in the ND data. Therefore, the present study gives an estimate of the strength of the martensite phase or the sharpness of the martensitic transition. Variation of individual moments and the change in the phase fraction obtained from the analysis of the ND data vividly show the change in the magneto-structural state of the material across the transition.",1702.00940v1 2019-05-21,Competition of L21 and XA Ordering in Fe2CoAl Heusler Alloy: A First-Principles Study,"The physical properties of Fe2CoAl (FCA) Heusler alloy are systematically investigated using the first-principles calculations within generalized gradient approximation (GGA) and GGA+U. The influence of atomic ordering with respect to the Wyckoff sites on the phase stability, magnetism and half metallicity in both the conventional L21 and XA phases of FCA is focused in this study. Various possible hypothetical structures viz., L21, XA-I, and XA-II are prepared by altering atomic occupancies at their Wyckoff sites. At first, we have determined the stable phase of FCA considering various non-magnetic (or paramagnetic), ferromagnetic (FM) and antiferromagnetic (AFM) configurations. Out of these, the ferromagnetic (FM) XA-I structure is found to be energetically most stable. The total magnetic moments per cell are not in agreement with the Slater-Pauling (SP) rule in any phases; therefore, the half-metallicity is not observed in any configurations. However, FM ordered XA-I type FCA shows 78% spin polarization at EF. Interestingly, the results of XA-I type FCA are closely matched with the experimental results.",1905.08476v2 2019-09-07,Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping,"Based on high-throughput density functional theory calculations, we investigated the effects of light interstitial H, B, C, and N atoms on the magnetic properties of cubic Heusler alloys, with the aim to design new rare-earth free permanent magnets. It is observed that the interstitial atoms induce significant tetragonal distortions, leading to 32 candidates with large ($>$ 0.4 MJ/m$^3$) uniaxial magneto-crystalline anisotropy energies (MAEs) and 10 cases with large in-plane MAEs. Detailed analysis following the the perturbation theory and chemical bonding reveals the strong MAE originates from the local crystalline distortions and thus the changes of the chemical bonding around the interstitials. This provides a valuable way to tailor the MAEs to obtain competitive permanent magnets, filling the gap between high performance Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.",1909.03275v1 2019-09-23,Giant magnetocaloric effect in Co2FeAl Heusler alloy nanoparticles,"A giant magnetocaloric effect across the ferromagnetic (FM) to paramagnetic (PM) phase transition was observed in chemically synthesized Co2FeAl Heusler alloy nanoparticles with a mean diameter of 16 nm. In our previous report, we have observed a significant enhancement in its saturation magnetization (Ms) and Curie temperature (Tc) as compared with the bulk counterpart. Motivated from those results, here, we aim to explore its magnetocaloric properties near the Tc. The magnetic entropy change shows a positive anomaly at 1252 K. Magnetic entropy change increases linearly with the magnetic field, and a large value of ~15 J/Kg-K is detected under a moderate field of 14 kOe. It leads to a net relative cooling power of 89 J/Kg for the magnetic field change of 14 kOe. To confirm the nature of magnetic phase transition, a detailed study of its magnetization is performed. The Arrott plot and nature of the universal curve conclude that FM to PM phase transition in the present system is of second-order.",1909.10201v4 2020-02-27,Ultrafast magnetization dynamics in half-metallic Co$_2$FeAl Heusler alloy,"We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy $\mathrm{Co_{2}FeAl}$, probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to results from electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we find that the demagnetization time ($\tau_{M}$) in films of $\mathrm{Co_{2}FeAl}$ is almost independent of varying structural order, and that it is similar to that in elemental 3d ferromagnets. In contrast, the slower process of magnetization recovery, specified by $\tau_{R}$, is found to occur on picosecond time scales, and is demonstrated to correlate strongly with the Gilbert damping parameter ($\alpha$). Our results show that $\mathrm{Co_{2}FeAl}$ is unique, in that it is the first material that clearly demonstrates the importance of the damping parameter in the remagnetization process. Based on these results we argue that for $\mathrm{Co_{2}FeAl}$ the remagnetization process is dominated by magnon dynamics, something which might have general applicability.",2002.12255v1 2020-07-12,"Magnetocaloric effect in Ni2(Mn,Cu)Ga0.84Al0.16 Heusler alloys","Polycrystalline Heusler compounds Ni2Mn0.75Cu0.25Ga0.84Al0.16 with a martensitic transition between ferromagnetic phases and Ni2Mn0.70Cu0.30Ga0.84Al0.16 with a magnetostructural transformation were investigated by magnetization and thermal measurements, both as a function of temperature and magnetic field. The compound Ni2Mn0.75Cu0.25Ga0.84Al0.16 presents a large magnetocaloric effect among magnetically aligned structures and its causes are explored. In addition, Ni2Mn0.70Cu0.30Ga0.84Al0.16 shows very high, although irreversible, entropy and adiabatic temperature change at room temperature under a magnetic field change 0-1 T. Improved refrigerant capacity is also a highlight of the 30% Cu material when compared to similar Ni2MnGa-based alloys.",2007.05899v2 2020-10-16,Visualizing half-metallic bulk band structure with multiple Weyl cones of the Heusler ferromagnet,"Using a well-focused soft X-ray synchrotron radiation beam, angle-resolved photoelectron spectroscopy was applied to a full-Heusler-type Co$_2$MnGe alloy to elucidate its bulk band structure. A large parabolic band at the Brillouin zone center and several bands that cross the Fermi level near the Brillouin zone boundary were identified in line with the results from first-principles calculations. These Fermi level crossings are ascribed to majority spin bands that are responsible for electron transport with extremely high spin polarization especially along the direction being perpendicular to the interface of magneto-resistive devices. The spectroscopy confirms there is no contribution of the minority spin bands to the Fermi surface, signifying half-metallicity for the alloy. Furthermore, two topological Weyl cones with band crossing points were identified around the $X$ point, yielding the conclusion that Co$_2$MnGe could exhibit topologically meaningful behavior such as large anomalous Hall and Nernst effects driven by the Berry flux in its half-metallic band structure.",2010.08415v1 2021-02-15,Prediction of a Heusler alloy with switchable metal-to-half-metal behavior,"We propose a ferromagnetic Heusler alloy that can switch between a metal and a half-metal. Thiseffect can provide tunable spintronics properties. Using the density functional theory (DFT) withreliable implementations of the electron correlation effects, we find Mn2ScSi total energy curvesconsisting of distinct branches with a very small energy difference. The phase at low lattice crystalvolume is a low magnetic half-metallic state while the phase at high lattice crystal volume is a highmagnetic metallic state. We suggest that the transition between half-metallic and metallic statescan be triggered by a triaxial contraction/expansion of the crystal lattice or by an external magneticfield if we assume that the lattice is cubic and remains cubic under expansion/contraction. However,the phase at high volume can also undergo an austenite-martensite phase transition because of thepresence of Jahn-Teller active3delectrons on the Mn atoms.",2102.07447v1 2021-06-06,Prediction of half-metallicity and spin-gapless semiconducting behavior in the new series of FeCr-based quaternary Heusler alloys: an ab initio study,"This paper presents a detailed investigation of FeCr-based quaternary Heusler alloys. By using ultrasoft pseudopotential, electronic and magnetic properties of the compounds are studied within the framework of Density Functional Theory (DFT) by using the Quantum Espresso package. The thermodynamic, mechanical, and dynamical stability of the compounds is established through the comprehensive study of different mechanical parameters and phonon dispersion curves. The meticulous study of elastic parameters such as bulk, Young's, shear moduli, etc. is done to understand different mechanical properties. The FeCr-based compounds containing also Yttrium are studied to redress the contradictory electronic and magnetic properties observed in the literature. The interesting properties like half-metallicity and spin-gapless semiconducting (SGS) behavior are realized in the compounds under study.",2106.03026v1 2021-11-29,"Half-metallic Ferromagnets, Spin Gapless Semiconductors, and Topological Semimetals Based on Heusler Alloys","A review of theoretical and experimental studies of the electronic structure, electronic and magnetic properties of various systems of Heusler alloys in the states of a half-metallic ferromagnet, a spin gapless semiconductor, and a topological semimetal is presented. These substances have unusual, highly sensitive to external influences, magnetic and electronic characteristics, which is associated with the presence of energy gaps and exotic excitations in them. The features of the behavior and evolution of the electronic structure and properties in each of these states, as well as during the transition between them, are considered. The possibility to purposefully control the properties of such materials is prospective for their practical application.",2111.14537v1 2022-08-06,Giant spin Hall effect in half-Heusler alloy topological semimetal YPtBi grown at low temperature,"Half-Heusler alloy topological semimetal YPtBi is a promising candidate for an efficient spin source material having both large spin Hall angle ${\theta}$$_{SH}$ and high thermal stability. However, high-quality YPtBi thin films with low bulk carrier density are usually grown at 600${\deg}$C, which exceeds the limitation of 400${\deg}$C for back end of line (BEOL) process. Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films grown at lower growth temperature down to 300${\deg}$C. Although ${\theta}$$_{SH}$ degraded with lowering the growth temperature to 300${\deg}$C due to degradation of the crystallinity, it was recovered by reducing the sputtering Ar gas pressure. We achieved a giant ${\theta}$$_{SH}$ up to 8.2 and demonstrated efficient spin-orbit torque magnetization switching by ultralow current density of ~10$^5$ A/cm$^2$ in YPtBi grown at 300${\deg}$C with the Ar gas pressure of 1 Pa. Our results provide the recipe to achieve giant ${\theta}$$_{SH}$ in YPtBi grown at lower growth temperature suitable for BEOL process.",2208.03413v1 2022-09-18,Superparamagnetic and metal-like Ru2TiGe: a propitious thermoelectric material,"We report a study of structural, magnetic, heat capacity and thermoelectric properties of a Rubased Heusler alloy, Ru2TiGe. The magnetic measurements reveal that at higher temperatures, diamagnetic and Pauli paramagnetic contributions dominate the magnetic behaviour whereas, at lower temperatures (T<= 20 K), superparamagnetic interaction among clusters is observed. Effect of such magnetic defects is also evident in the electrical resistivity behaviour at lower temperatures. Though the temperature dependence of resistivity exhibits a metal-like nature, the large value of Seebeck coefficient leads to an appreciable power factor of the order of 1 mW/mK2 at 300 K. Large power factor as well as low thermal conductivity results in a value of ZT = 0.025 at 390 K for Ru2TiGe that is orders of magnitude higher than that of the other pure Heusler alloys and point towards its high potential for practical thermoelectric applications.",2209.08474v1 2022-11-22,Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl,"Heusler alloys based magnetic tunnel junctions can potentially provide high magnetoresistance, small damping and fast switching. Here junctions with Co2FeAl as a ferromagnetic electrode are fabricated by room temperature sputtering on Si/SiO2 substrates. The doping of Boron in Co2FeAl is found to have a large positive impact on the structural, magnetic and transport properties of the junctions, with a reduced interfacial roughness and substantial improved tunneling magnetoresistance. A two-level magnetoresistance is also observed in samples annealed at low temperature, which is believed to be related to the memristive effect of the tunnel barrier with impurities.",2211.12448v1 2023-09-11,Experimental realization of a high Curie temperature CoFeRuSn quaternary Heusler alloy for spintronic applications,"We synthesize CoFeRuSn equiatomic quaternary Heusler alloy using arc-melt technique and investigate its structural, magnetic and transport properties. The room temperature powder X-ray diffraction analysis reveals that CoFeRuSn crystallizes in cubic crystal structure with small amount of DO3 - disorder. The field dependence of magnetization shows non-zero but small hysteresis and saturation behavior up to room temperature, indicating soft ferromagnetic nature of CoFeRuSn. The magnetic moment estimated from the magnetization data is found to be 4.15 {\mu}B / f.u., which is slightly less than the expected Slater-Pauling rule. The deviation in the value of experimentally observed moment from the theoretical value might be due to small disorder in the crystal. The low temperature fit to electrical resistivity data show absence of quadratic temperature dependence of resistivity, suggesting half-metallic behavior of CoFeRuSn. The high Curie temperature and possible half-metallic behavior of CoFeRuSn make it a highly promising candidate for room temperature spintronic applications.",2309.05493v1 2023-11-26,Machine Learning-based estimation and explainable artificial intelligence-supported interpretation of the critical temperature from magnetic ab initio Heusler alloys data,"Machine Learning (ML) has impacted numerous areas of materials science, most prominently improving molecular simulations, where force fields were trained on previously relaxed structures. One natural next step is to predict material properties beyond structure. In this work, we investigate the applicability and explainability of ML methods in the use case of estimating the critical temperature for magnetic Heusler alloys calculated using ab initio methods determined materials-specific magnetic interactions and a subsequent Monte Carlo (MC) approach. We compare the performance of regression and classification models to predict the range of the critical temperature of given compounds without performing the MC calculations. Since the MC calculation requires computational resources in the same order of magnitude as the density-functional theory (DFT) calculation, it would be advantageous to replace either step with a less computationally intensive method such as ML. We discuss the necessity to generate the magnetic ab initio results to make a quantitative prediction of the critical temperature. We used state-of-the-art explainable artificial intelligence (XAI) methods to extract physical relations and deepen our understanding of patterns learned by our models from the examined data.",2311.15423v1 2024-03-27,THz probing of non-trivial topological states in Co2MnGe Heusler alloy thin films,"Co2MnGe (CMG) has been demonstrated recently as a half-metallic ferromagnetic Heusler alloy which possesses a topologically non-trivial band structure. This behavior is unique to such systems and hence warrants extensive experimental exploration for potential spintronic and chirality sensitive optoelectonic applications. Here, we demonstrate that an epitaxial thin film of CMG acts as a source of THz radiation upon photoexcitation by optical femtosecond laser pulses. Detailed experiments have revealed that a large contribution to THz emission occurs due to nonmagnetic or spin-independent origin, however, significant contribution in the THz generation is evidenced through excitation light helicity dependent circular photogalvanic effect (CPGE) confirming the presence of topologically non-trivial carriers. Furthermore, we show that not only the topological contribution is easily suppressed but also the overall THz generation efficiency is also affected adversely for the epitaxial films grown at high substrate temperatures.",2403.18332v1 2015-06-23,Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias,"The discovery of materials with improved functionality can be accelerated by rational material design. Heusler compounds with tunable magnetic sublattices allow to implement this concept to achieve novel magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant exchange bias (EB) of more than 3 T and a similarly large coercivity are established. The large exchange anisotropy originates from the exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. We demonstrate the applicability of our design concept on a second material, Mn-Fe-Ga, with a magnetic transition above room temperature, exemplifying the universality of the concept and the feasibility of room-temperature applications. Our study points to a new direction for novel magneto-electronic devices. At the same time it suggests a new route for realizing rare-earth free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.",1506.07028v1 2021-07-19,Impact of local arrangement of Fe and Ni in Fe-Ni-Al Heusler alloys on the phase stability and magnetocrystalline anisotropy,"On the basis of the density functional calculations in combination with the supercell approach, we report on a complete study of the influences of atomic arrangement and Ni substitution for Al on the ground state structural and magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss systematically the competition between five cubic Heusler-type structures formed by shuffles of Fe and Ni atoms to reveal routes for improving the phase stability and magnetic properties, in particular magnetocrystalline anisotropy~(MAE). We predict that in case of Fe$_2$NiAl the ground state cubic structure with alternated layers of Fe and Ni possesses the highest uniaxial MAE which twice larger than that for the tetragonal L1$_0$ FeNi. The successive Ni doping at Al sublattice leads to a change of ground state structure and to reduce of the MAE. In addition, the phase stability against the decomposition into the stable systems at finite-temperatures is discussed. All~Ni-rich Fe$_2$Ni$_{1+x}$Al$_{1-x}$ are turned to be decomposed into a dual-phase consisting of Fe$_2$NiAl and FeNi.",2107.08804v2 2019-07-05,Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy,"Materials suitable for magnonic crystals demand low magnetic damping and long spin wave (SW) propagation distance. In this context Co based Heusler compounds are ideal candidates for magnonic based applications. In this work, antidot arrays (with different shapes) of epitaxial $\mathrm{Co}_2\mathrm{Fe}_{0.4}\mathrm{Mn}_{0.6}\mathrm{Si}$ (CFMS) Heusler alloy thin films have been prepared using e-beam lithography and sputtering technique. Magneto-optic Kerr effect and ferromagnetic resonance analysis have confirmed the presence of dominant cubic and moderate uniaxial magnetic anisotropies in the thin films. Domain imaging via x-ray photoemission electron microscopy on the antidot arrays reveals chain like switching or correlated bigger domains for different shape of the antidots. Time-resolved MOKE microscopy has been performed to study the precessional dynamics and magnonic modes of the antidots with different shapes. We show that the optically induced spin-wave spectra in such antidot arrays can be tuned by changing the shape of the holes. The variation in internal field profiles, pinning energy barrier, and anisotropy modifies the spin-wave spectra dramatically within the antidot arrays with different shapes. We further show that by combining the magnetocrystalline anisotropy with the shape anisotropy, an extra degree of freedom can be achieved to control the magnonic modes in such antidot lattices.",1907.02746v1 2014-02-07,Fermi sea term in the relativistic linear muffin-tin-orbital transport theory for random alloys,"We present a formulation of the so-called Fermi sea contribution to the conductivity tensor of spin-polarized random alloys within the fully relativistic tight-binding linear muffin-tin-orbital (TB-LMTO) method and the coherent potential approximation (CPA). We show that the configuration averaging of this contribution leads to the CPA-vertex corrections that are solely due to the energy dependence of the average single-particle propagators. Moreover, we prove that this contribution is indispensable for the invariance of the anomalous Hall conductivities with respect to the particular LMTO representation used in numerical implementation. Ab initio calculations for cubic ferromagnetic 3d transition metals (Fe, Co, Ni) and their random binary alloys (Ni-Fe, Fe-Si) indicate that the Fermi sea term is small against the dominating Fermi surface term. However, for more complicated structures and systems, such as hexagonal cobalt and selected ordered and disordered Co-based Heusler alloys, the Fermi sea term plays a significant role in the quantitative theory of the anomalous Hall effect.",1402.1643v1 2015-05-01,"Half-metallic state and magnetic properties versus the lattice constant in Zr2RhZ (Z = Al, Ga, In) Heusler alloys","The half metallic and magnetic properties of Zr2RhZ (Z = Al, Ga, In) alloys with an Hg2CuTi-type structure were systematically investigated using the first-principle calculations. Zr2RhZ (Z = Al, Ga, In) alloys are predicted to be half-metallic ferrimagnets at their equilibrium lattice constants. The Zr2Rh-based alloys have Mt (the total magnetic moment per unit cell) and Zt (the valence concentration) values that in agreement with Slater-Pauling rule Mt = Zt -18. The half-metallic properties and the magnetic properties at different lattice constants are discussed in detail. We expect that our results may trigger Zr2RhZ (Z = Al, Ga, In) applying in the future spintronics field.",1505.00203v1 2016-11-08,Geometry of Adaptive Martensite in Ni-Mn-based Heusler alloys,"Modulated martensites play an important role in magnetic shape memory alloys, because all functional properties are closely connected to the twin microstructure and the phase boundary. The nature of the modulated martensites is still unclear. One approach is the concept of adaptive martensite, which regards all modulated phases as nanotwinned microstructures. In this article, we use the Ni-Mn-based shape memory alloys as an example to show the geometric rationale behind this concept using analytic equations based on the phenomenological theory of martensite. This could enhance discussions about the implications of the adaptive martensite by showing the exact relations between the various unit cells used to describe the structure. We use the concept to discuss the compatibility at the habit plane, the nature of high-order twin boundaries and the dependence of the lattice constants on the different types of modulation.",1611.02535v2 2020-10-06,Tailoring magnetocaloric effect in all-d-metal Ni-Co-Mn-Ti Heusler alloys: a combined experimental and theoretical study,"Novel Ni-Co-Mn-Ti all-d-metal Heusler alloys are exciting due to large multicaloric effects combined with enhanced mechanical properties. An optimized heat treatment for a series of these compounds leads to very sharp phase transitions in bulk alloys with isothermal entropy changes of up to 38 J kg$^{-1}$ K$^{-1}$ for a magnetic field change of 2 T. The differences of as-cast and annealed samples are analyzed by investigating microstructure and phase transitions in detail by optical microscopy. We identify different grain structures as well as stoichiometric (in)homogenieties as reasons for differently sharp martensitic transitions after ideal and non-ideal annealing. We develop alloy design rules for tuning the magnetostructural phase transition and evaluate specifically the sensitivity of the transition temperature towards the externally applied magnetic fields ($\frac{dT_t}{\mu_0dH}$) by analyzing the different stoichiometries. We then set up a phase diagram including martensitic transition temperatures and austenite Curie temperatures depending on the e/a ratio for varying Co and Ti content. The evolution of the Curie temperature with changing stoichiometry is compared to other Heusler systems. Density Functional Theory calculations reveal a correlation of T$_C$ with the stoichiometry as well as with the order state of the austenite. This combined approach of experiment and theory allows for an efficient development of new systems towards promising magnetocaloric properties. Direct adiabatic temperature change measurements show here the largest change of -4 K in a magnetic field change of 1.93 T for Ni$_{35}$Co$_{15}$Mn$_{37}$Ti$_{13}$.",2010.02620v2 2015-06-29,Giant magnetocaloric effect from reverse martensitic transformation in Ni-Mn-Ga-Cu ferromagnetic shape memory alloys,"In an effort to produce Giant Magnetocaloric effect (GMCE) near room temperature, in a first ever such study, the austenite transformation temperature (As) was fine tuned to ferromagnetic Curie temperature (TC) in Ferromagnetic Shape Memory Alloys (FSMA) and a large GMCE of delta-SM = - 81.75 J/Kg-K was achieved in Ni50Mn18.5Cu6.5Ga25 alloy during reverse martensitic transformation (heating cycle) for a magnetic field change of 9 T at 302.5 K. Fine tuning of As with TC was achieved by Cu substitution in Ni50Mn25-xCuxGa25 (0< x < 7.0)-based FSMAs. Characterizations of these alloys were carried out using Optical and Scanning Electron Microscopy, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and DC magnetization measurements. Addition of Cu to stoichiometric Heusler type Ni2MnGa increases the martensitic transformation temperatures and decreases TC. Concurrently, DSM increases with Cu addition and peaks at 6.5 at. % Cu for which there is a virtual overlap between TC and As. Maximum Refrigerant Capacity (RCP) of 327.01 J/Kg was also achieved in the heating cycle for 9 T field change at 302.5 K. Corresponding values for the cooling cycle measurements (measured during forward transformation) were 30.4 J/Kg-K and 123.52 J/Kg respectively for the same 6.5 at. % Cu sample and same thermo-magnetic conditions.",1506.08709v2 2006-01-30,Electronic structure and spectroscopy of the quaternary Heusler alloy Co$_2$Cr$_{1-x}$Fe$_{x}$Al,"Quaternary Heusler alloys Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe ratio $x$ were investigated experimentally and theoretically. The electronic structure and spectroscopic properties were calculated using the full relativistic Korringa-Kohn-Rostocker method with coherent potential approximation to account for the random distribution of Cr and Fe atoms as well as random disorder. Magnetic effects are included by the use of spin dependent potentials in the local spin density approximation. Magnetic circular dichroism in X-ray absorption was measured at the $L_{2,3}$ edges of Co, Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to determine element specific magnetic moments. Calculations and measurements show an increase of the magnetic moments with increasing iron content. Resonant (560eV - 800eV) soft X-ray as well as high resolution - high energy ($\geq 3.5$keV) hard X-ray photo emission was used to probe the density of the occupied states in Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al.",0601670v1 2008-02-18,Ab-initio determined electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys; the role of interfaces and defects,"Using state-of-the-art first-principles calculations we study the properties of the ferromagnetic Heusler compounds NiYSi where Y stands for V, Cr or Mn. NiCrSi and NiMnSi contrary to NiVSi are half-metallic at their equilibrium lattice constant exhibiting integer values of the total spin magnetic moment and thus we concentrate on these two alloys. The minority-spin gap has the same characteristics as for the well-known NiMnSb alloy being around $\sim$1 eV. Upon tetragonalization the gap is present in the density of states even for expansion or contraction of the out-of-plane lattice parameter by 5%. The Cr-Cr and Mn-Mn interactions make ferromagnetism extremely stable and the Curie temperature exceeds 1000 K for NiMnSi. Surface and interfaces with GaP, ZnS and Si semiconductors are not half-metallic but in the case of NiCrSi the Ni-based contacts present spin-polarization at the Fermi level over 90%. Finally, we show that there are two cases of defects and atomic-swaps. The first-ones which involve the Cr(Mn) and Si atoms induce states at the edges of the gap which persists for a moderate-concentration of defects. Defects involving Ni atoms induce states localized within the gap completely destroying the half-metallicity. Based on single-impurity calculations we associate these states to the symmetry of the crystal.",0802.2531v1 2016-10-19,Bismuth based Half Heusler Alloys with giant thermoelectric figure of merit,"Half Heusler (HH) thermoelectric alloys provide a wide platform to choose materials with non-toxic and earth abundant elements. This article presents an ab-initio theoretical evaluation of electrical and thermal transport properties of three Bismuth-based most promising thermoelectric alloys, selected out of 54 stable HH compounds. These are brand new compounds which are recently proposed to be stable (Nature Chem. 7, 308 (2015)) and may have interesting properties. The calculated band structure of the three compounds, namely HfRhBi, ZrIrBi and ZrRhBi, served as a hint for their promising thermoelectric properties. To gain confidence on the theoretical predictions of these unreported systems, we first checked our calculated results for a well studied similar compound, ZrNiSn, and showed reasonable agreement with the measured ones. HfRhBi and ZrIrBi turn out to be narrow band gap while ZrRhBi is a moderate band gap semiconductor. A detailed study of the carrier concentration and temperature dependance of the Seebeck coefficient (S), Power factor (S$^2 \sigma$), lattice ($\kappa_L$) and electronic ($\kappa_e$) thermal conductivity and hence the figure of merit (ZT) is carried out. In contrast to most promising known thermoelectric materials, we found high power factor for these materials (highest S$^2 \sigma\sim$17.36 mWm$^{-1}$K$^{-2}$ for p-type ZrIrBi). All the three systems (specially p-type) show high figure of merit, with ZT value as high as 0.45 for ideal crystal. Maximum ZT and the corresponding optimal n- and p-type doping concentrations ($n_c$) are calculated for all the three compounds, which shall certainly pave guidance to future experimental work.",1610.06038v2 2017-04-01,"Native defects in the Co$_2$Ti$Z$ ($Z=$ Si, Ge, Sn) full Heusler alloys: formation and influence on the thermoelectric properties","We have performed first-principles investigations on the native defects in the full Heusler alloys Co$_2$Ti$Z$ ($Z$ one of the group IV elements Si, Ge, Sn), determining their formation energies and how they influence the transport properties. We find that Co vacancies (Vc) in all compounds and the Ti$_\text{Sn}$ anti-site exhibit negative formation energies. The smallest positive values occur for Co in excess on anti-sites (Co$_Z$ or Co$_\text{Ti}$) and for Ti$_Z$. The most abundant native defects were modeled as dilute alloys, treated with the coherent potential approximation in combination with the multiple-scattering theory Green function approach. The self-consistent potentials determined this way were used to calculate the residual resistivity via the Kubo-Greenwood formula and, based on its energy dependence, the Seebeck coefficient of the systems. The latter is shown to depend significantly on the type of defect, leading to variations that are related to subtle, spin-orbit coupling induced, changes in the electronic structure above the half-metallic gap. Two of the systems, Vc$_\text{Co}$ and Co$_Z$, are found to exhibit a negative Seebeck coefficient. This observation, together with their low formation energy, offers an explanation for the experimentally observed negative Seebeck coefficient of the Co$_2$Ti$Z$ compounds as being due to unintentionally created native defects.",1704.00149v2 2017-10-06,Relative Cooling Power Enhancement by Tuning Magneto-structural Stability in Ni-Mn-In Heusler Alloys,"Off-stoichiometric Ni$_2$MnIn Heusler alloys have drawn recent attention due to their large magnetocaloric entropy change associated with the first-order magneto-structural transition. Here we present crystal structural, calorimetric and magnetic studies of three compositions. Temperature-dependent X-ray diffraction shows clear structural transition from a 6M modulated monoclinic to a L2$_1$ cubic. A significant enhancement of relative cooling power (RCP) was achieved by tuning the magnetic and structural stability through minor compositional changes, with the measured results quantitatively close to the prediction as a function of the ratio between the martensitic transition ($T_m$) temperature and austenite Curie temperature ($T_C$) although the maximal magnetic induced entropy change ($\Delta S_{max}$) reduction is observed in the same time. The results provided an evaluation guideline of RCPs as well as magnetic-induced entropy change in designing practical active materials.",1710.02522v6 2020-10-22,Multicaloric effects in Metamagnetic Heusler Ni-Mn-In under uniaxial stress and magnetic field,"The world's growing hunger for artificial cold on the one hand, and the ever more stringent climate targets on the other, pose an enormous challenge to mankind. Novel, efficient and environmentally friendly refrigeration technologies based on solid-state refrigerants can offer a way out of the problems arising from climate-damaging substances used in conventional vapor-compressors. Multicaloric materials stand out because of their large temperature changes which can be induced by the application of different external stimuli such as a magnetic, electric, or a mechanical field. Despite the high potential for applications and the interesting physics of this group of materials, only few studies focus on their investigation by direct methods. In this paper, we report on the advanced characterization of all relevant physical quantities that determine the multicaloric effect of a Ni-Mn-In Heusler compound. We have used a purpose-designed calorimeter to determine the isothermal entropy and adiabatic temperature changes resulting from the combined action of magnetic field and uniaxial stress on this metamagnetic shape-memory alloy. From these results, we can conclude that the multicaloric response of this alloy by appropriate changes of uniaxial stress and magnetic field largely outperforms the caloric response of the alloy when subjected to only a single stimulus. We anticipate that our findings can be applied to other multicaloric materials, thus inspiring the development of refrigeration devices based on the multicaloric effect.",2010.11511v1 2020-11-03,Fully-Compensated Ferrimagnetic Spin Filter Materials within the Cr$\textit{M}\textit{N}$Al Equiatomic Quaternary Heusler Alloys,"XX'YZ equiatomic quaternary Heusler alloys (EQHA's) containing Cr, Al, and select Group IVB elements ($\textit{M}$ = Ti, Zr, Hf) and Group VB elements ($\textit{N}$ = V, Nb, Ta) were studied using state-of-the-art density functional theory to determine their effectiveness in spintronic applications. Each alloy is classified based on their spin-dependent electronic structure as a half-metal, a spin gapless semiconductor, or a spin filter material. We predict several new fully-compensated ferrimagnetic spin filter materials with small electronic gaps and large exchange splitting allowing for robust spin polarization with small resistance. CrVZrAl, CrVHfAl, CrTiNbAl, and CrTiTaAl are identified as particularly robust spin filter candidates with an exchange splitting of $\sim 0.20$ eV. In particular, CrTiNbAl and CrTiTaAl have exceptionally small band gaps of $\sim 0.10$ eV. Moreover, in these compounds, a spin asymmetric electronic band gap is maintained in 2 of 3 possible atomic arrangements they can take, making the electronic properties less susceptible to random site disorder. In addition, hydrostatic stress is applied to a subset of the studied compounds in order to determine the stability and tunability of the various electronic phases. Specifically, we find the CrAlV$\textit{M}$ subfamily of compounds to be exceptionally sensitive to hydrostatic stress, yielding transitions between all spin-dependent electronic phases.",2011.01389v1 2023-07-31,Ballistic spin-transport properties of magnetic tunnel junctions with MnCr-based ferrimagnetic quaternary Heusler alloys,"We investigate the suitability of nearly half-metallic ferrimagnetic quaternary Heusler alloys, CoCrMnZ (Z=Al, Ga, Si, Ge) to assess the feasibility as electrode materials of MgO-based magnetic tunnel junctions (MTJ). Low magnetic moments of these alloys originated from the anti-ferromagnetic coupling between Mn and Cr spins ensure a negligible stray field in spintronics devices as well as a lower switching current required to flip their spin direction. We confirmed mechanical stability of these materials from the evaluated values of elastic constants, and the absence of any imaginary frequency in their phonon dispersion curves. The influence of swapping disorders on the electronic structures and their relative stability are also discussed. A high spin polarization of the conduction electrons are observed in case of CoCrMnZ/MgO hetrojunctions, independent of terminations at the interface. Based on our ballistic transport calculations, a large coherent tunnelling of the majority-spin $s$-like $\Delta_1$ states can be expected through MgO-barrier. The calculated tunnelling magnetoresistance (TMR) ratios are in the order of 1000\%. A very high Curie temperatures specifically for CoCrMnAl and CoCrMnGa, which are comparable to $bcc$ Co, could also yield a weaker temperature dependece of TMR ratios for CoCrMnAl/MgO/CoCrMnAl (001) and CoCrMnGa/MgO/CoCrMnGa (001) MTJ.",2307.16442v1 2024-01-22,Off-stoichiometric effect on magnetic and electron transport properties of Fe$_2$VAl$_{1.35}$ in respect to Ni$_2$VAl; Comparative study,"Density functional theory (DFT) calculations confirm that the structurally ordered Fe$_2$VAl Heusler alloy is nonmagnetic narrow-gap semiconductor. This compound is apt to form various disordered modifications with high concentration of antisite defects. We study the effect of structural disorder on the electronic structure, magnetic, and electronic transport properties of the full Heusler alloy Fe$_2$VAl and its off-stoichiometric equivalent Fe$_2$VAl$_{1.35}$. Data analysis in relation to {\it ab initio} calculations indicates an appearance of antisite disorder mainly due to Fe--V and Fe--Al stoichiometric variations. The data for weakly magnetic Fe$_2$VAl$_{1.35}$ are discussed in respect to Ni$_2$VAl. Fe$_2$VAl$_{1.35}$ can be classified as a nearly ferromagnetic metal with a pronounced spin glassy contribution, which, however, does not give a predominant effect on its thermoelectric properties. The figure of merit $ZT$ is at 300 K about 0.05 for the Fe sample and 0.02 for Ni one, respectively. However, it is documented that the narrow $d$ band resulting from Fe/V site exchange can be responsible for the unusual temperature dependencies of the physical properties of the Fe2TiAl$_{1.35}$ alloy, characteristic of strongly correlated electron systems. As an example, the magnetic susceptibility of Fe$_2$VAl$_{1.35}$ exhibits singularity characteristic of a Griffiths phase, appearing as an inhomogeneous electronic state below $T_G\sim 200$ K. We also performed numerical analysis which supports the Griffiths phase scenario.",2401.12218v1 2016-11-21,Adaptive modulation in Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy,"The origin of incommensurate structural modulation in Ni-Mn based Heusler type magnetic shape memory alloys (MSMAs) is still an unresolved issue inspite of intense focus on this due to its role in the magnetic field induced ultra-high strains. In the archetypal MSMA Ni2MnGa, the observation of non-uniform displacement of atoms from their mean positions in the modulated martensite phase, premartensite phase and charge density wave as well as the presence of phason broadening of satellite peaks have been taken in support of the electronic instability model linked with a soft acoustic phonon. We present here results of a combined high resolution synchrotron x-ray powder diffraction (SXRPD) and neutron powder diffraction (NPD) study on Ni2Mn1.4In0.6 using (3+1)D superspace group approach, which reveal not only uniform atomic displacements in the modulated structure of the martensite phase with physically acceptable ordered magnetic moments in the antiferromagnetic phase at low temperatures but also the absence of any premartensite phase and phason broadening of the satellite peaks. Our HRTEM studies and first principles calculations of the ground state also support uniform atomic displacements predicted by powder diffraction studies. All these observations suggest that the structural modulation in the martensite phase of Ni2Mn1.4In0.6 MSMA can be explained in terms of the adaptive phase model. The present study underlines the importance of superspace group analysis using complimentary SXRPD and NPD in understanding the physics of the origin of modulation as well as the magnetic and the modulated ground states of the Heusler type MSMAs. Our work also highlights the fact that the mechanism responsible for the origin of modulated structure in different Ni-Mn based MSMAs may not be universal and it must be investigated thoroughly in different alloy compositions.",1611.06688v2 2021-05-14,"Understanding Magnetic Phase Coexistence in Ru$_2$Mn$_{1-x}$Fe$_x$Sn Heusler Alloys: A Neutron Scattering, Thermodynamic, and Phenomenological Analysis","The random substitutional solid solution between the antiferromagnetic (AFM) full-Heusler alloy Ru$_2$MnSn and the ferromagnetic (FM) full-Heusler alloy Ru$_2$FeSn provides a rare opportunity to study FM-AFM phase competition in a near-lattice-matched, cubic system, with full solubility. At intermediate $x$ in Ru$_2$Mn$_{1-x}$Fe$_x$Sn this system displays suppressed magnetic ordering temperatures, spatially coexisting FM and AFM order, and strong coercivity enhancement, despite rigorous chemical homogeneity. Here, we construct the most detailed temperature- and $x$-dependent understanding of the magnetic phase competition and coexistence in this system to date, combining wide-temperature-range neutron diffraction and small-angle neutron scattering with magnetometry and specific heat measurements on thoroughly characterized polycrystals. A complete magnetic phase diagram is generated, showing FM-AFM coexistence between $x \approx 0.30$ and $x \approx 0.70$. Important new insight is gained from the extracted length scales for magnetic phase coexistence (25-100 nm), the relative magnetic volume fractions and ordering temperatures, in addition to remarkable $x$-dependent trends in magnetic and electronic contributions to specific heat. An unusual feature in the magnetic phase diagram (an intermediate FM phase) is also shown to arise from an extrinsic effect related to a minor Ru-rich secondary phase. The established magnetic phase diagram is then discussed with the aid of phenomenological modeling, clarifying the nature of the mesoscale phase coexistence with respect to the understanding of disordered Heisenberg models.",2105.06629v1 2023-08-18,Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films,"Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high Curie temperature (TC) and sizeable spin polarization have emerged as potential candidates for tunable spintronic applications. We report comprehensive investigation of the temperature dependent ANE and intrinsic longitudinal spin Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm) film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (= 0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $\mu$V/K/$\Omega$ at room temperature which is twice larger than that of the half-metallic ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5 $\mu$V/K/$\Omega$). We show that both ANE and LSSE coefficients follow identical temperature dependences and exhibit a maximum at $\cong$ 225 K which is understood as the combined effects of inelastic magnon scatterings and reduced magnon population at low temperatures. Our analyses not only indicate that the extrinsic skew scattering is the dominating mechanism for ANE in these films but also provide critical insights into the functional form of the observed temperature dependent LSSE at low temperatures. Furthermore, by employing radio frequency transverse susceptibility and broadband ferromagnetic resonance in combination with the LSSE measurements, we establish a correlation among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the CoFeCrGa thin films, which will be beneficial for fabricating tunable and highly efficient Heusler alloys based spincaloritronic nanodevices.",2308.09843v1 2016-01-22,Phase Separation and Superparamagnetism in the Martensitic Phase of $Ni_{50-x}Co_{x}Mn_{40}Sn_{10}$,"$Ni_{50-x}Co_{x}Mn_{40}Sn_{10}$ shape memory alloys in the approximate range $5 \le x \le 10$ display desirable properties for applications as well as intriguing magnetism. These off-stoichiometric Heusler alloys undergo a martensitic phase transformation at a temperature $T_{M}$ of 300 - 400 K, from ferromagnetic (F) to nonferromagnetic, with unusually low thermal hysteresis and a large change in magnetization. The low temperature magnetic structures in the martensitic phase of such alloys, which are distinctly inhomogeneous, are of great interest but are not well understood. Our present use of spin echo NMR, in the large hyperfine fields at $^{55}Mn$ sites, provides compelling evidence that nanoscale magnetic phase separation into F and antiferromagnetic (AF) regions occurs below $T_{M}$ in alloys with x in the range 0 to 7. At finite Co substitution the F regions are found to be of two distinct types, corresponding to high and low local concentrations of Co on Ni sites. Estimates of the size distributions of both the F and AF nanoregions have been made. At x = 7 the AF component is not long-range ordered, even below 4 K, and is quite different to the AF component found at x = 0; by x = 14 the F phase is completely dominant. Of particular interest, we find, for x = 7, that field cooling leads to dramatic changes in the AF regions. These findings provide insight into the origins of magnetic phase separation and superparamagnetism in these complex alloys, particularly their intrinsic exchange bias, which is of considerable current interest.",1601.05993v1 2018-04-11,NMR and the antiferromagnetic crystal phase regions in rapidly quenched ribbons and in alloys of the type $Cu-Mn-Al$,"It was shown that anomalous resistivity behavior of the $Cu-Mn-Al$ ribbons is explained by the s-d interaction between conduction electrons and the clustered Mn atoms. While nuclear magnetic resonance measurements show the antiferromagnetic and ferromagnetic clusters of Mn atom coexisting without long-range order, it is an interesting problem to study magnetic resonance properties also for the antiferromagnetic crystal phase regions (which have long-range order for larger regions) and which may also occur in these ribbons. The Heusler Type $Cu-Mn-Al$ Alloy has a composition half way between $Cu_{2}MnAl$ and $Cu_{3}Al$. Electron microscopy of the premartensitic $\beta Cu-Zn-Al$ alloy has shown that the $\beta Cu-Zn-Al$ alloy quenched from high temperature has the electron diffraction patterns of this alloy well explained by the model with the existence of small particles with an orthorhombic structure. It was noted that an important aspect of improvement in the material properties is to create a nanostructured state in matrix, which has significant advantages in magnetic and mechanical characteristics in contrast to the bulk materials in crystalline or amorphous state. It is an interesting problem to study magnetic resonance properties not only for the Mn atoms and clusters without long-range order but also for the antiferromagnetic crystal phase regions (which have long-range order for larger regions) which may also occur in ribbons. This is the aim of our paper.",1804.04196v1 2023-11-30,Vanishing of the anomalous Hall effect and enhanced carrier mobility in the spin-gapless ferromagnetic Mn2CoGa1-xAlx alloys,"Spin gapless semiconductor (SGS) has attracted long attention since its theoretical prediction, while concrete experimental hints are still lack in the relevant Heusler alloys. Here in this work, by preparing the series alloys of Mn2CoGa1-xAlx (x=0, 0.25, 0.5, 0.75 and 1), we identified the vanishing of anomalous Hall effect in the ferromagnetic Mn2CoGa (or x=0.25) alloy in a wide temperature interval, accompanying with growing contribution from the ordinary Hall effect. As a result, comparatively low carrier density (1020 cm-3) and high carrier mobility (150 cm2/Vs) are obtained in Mn2CoGa (or x=0.25) alloy in the temperature range of 10-200K. These also lead to a large dip in the related magnetoresistance at low fields. While in high Al content, despite the magnetization behavior is not altered significantly, the Hall resistivity is instead dominated by the anomalous one, just analogous to that widely reported in Mn2CoAl. The distinct electrical transport behavior of x=0 and x=0.75 (or 1) is presently understood by their possible different scattering mechanism of the anomalous Hall effect due to the differences in atomic order and conductivity. Our work can expand the existing understanding of the SGS properties and offer a better SGS candidate with higher carrier mobility that can facilitate the application in the spin-injected related devices.",2311.18335v1 2003-11-19,Shape memory ferromagnets,"In ferromagnetic alloys with shape memory large reversible strains can be obtained by rearranging the martensitic domain structure by a magnetic field. Magnetization through displacement of domain walls is possible in the presence of high magnetocrystalline anisotropy, when martensitic structure rearrangement is energetically favorable compared to the reorientation of magnetic moments. In ferromagnetic Heusler alloys Ni$_{2+x}$Mn$_{1-x}$Ga the Curie temperature exceeds the martensitic transformation temperature. The fact that these two temperatures are close to room temperature offers the possibility of magnetically controlling the shape and size of ferromagnets in the martensitic state. In Ni$_{2+x}$Mn$_{1-x}$Ga single crystals, a reversible strain of $\sim 6$% is obtained in fields of $\sim 1$ T.",0311433v1 2003-12-04,Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition,"The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with coupled magnetic and structural (martensitic) phase transitions were studied experimentally and theoretically. The magnetocaloric effect was measured by a direct method in magnetic fields 0-26 kOe at temperatures close to the magnetostructural transition temperature. For theoretical description of the alloy properties near the magnetostructural transition a statistical model is suggested, that takes into account the coexistence of martensite and austenite domains in the vicinity of martensite transformation point.",0312110v1 2004-05-07,Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys,"A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19) Heusler alloys undergoing structural martensite-austenite transformations while in ferromagnetic state has been performed. From measurements of spontaneous magnetization, Ms(T), jumps \Delta M at structural phase transitions were determined. Virtual Curie temperatures of the martensite were estimated from the comparison of magnetization in martensitic and austenitic phases. Both saturation magnetic moments in ferromagnetic state and effective magnetic moments in paramagnetic state of Mn and Ni atoms were estimated and the influence of delocalization effects on magnetism in these alloys was discussed. The experimental results obtained show that the shift of martensitic transition temperature depends weakly on composition. The values of this shift are in good correspondence with Clapeyron-Clausius formalism taking into account the experimental data on latent heat at martensite-austenite transformations.",0405134v1 2007-09-01,Local atomic arrangement and martensitic transformation in Ni$_{50}$Mn$_{35}$In$_{15}$: An EXAFS Study,"Heusler alloys that undergo martensitic transformation in ferromagnetic state are of increasing scientific and technological interest. These alloys show large magnetic field induced strains upon martensitic phase change thus making it a potential candidate for magneto-mechanical actuation. The crystal structure of martensite is an important factor that affects both the magnetic anisotropy and mechanical properties of such materials. Moreover, the local chemical arrangement of constituent atoms is vital in determining the overall physical properties. Ni$_{50}$Mn$_{35}$In$_{15}$ is one such ferromagnetic shape memory alloy that displays exotic properties like large magnetoresistance at moderate field values. In this work, we present the extended x-ray absorption fine-structure measurements (EXAFS) on the bulk Ni$_{50}$Mn$_{35}$In$_{15}$ which reveal the local structural change that occurs upon phase transformation. The change in the bond lengths between different atomic species helps in understanding the type of hybridization which is an important factor in driving such Ni-Mn based systems towards martensitic transformation.",0709.0030v1 2009-06-19,Lattice dynamics in magnetic superelastic Ni-Mn-In alloys. Neutron scattering and ultrasonic experiments,"Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two single crystals of Ni-Mn-In Heusler alloys close to Ni$_{50}$Mn$_{34}$In$_{16}$ magnetic superelastic composition. The paper reports the experimental determination of the low-lying phonon dispersion curves and the elastic constants for this alloy system. We found that the frequencies of the TA$_{2}$ branch are relatively low and it exhibits a small dip anomaly at a wave number $\xi_{0} \approx 1/3$, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear elastic constant $C'=(C_{11}-C_{12})/2$. Both temperature softenings are typical for bcc based solids which undergo martensitic transformations and reflect the dynamical instability of the cubic lattice against shearing of $\{110\}$ planes along $<1\bar{1}0>$ directions. Additionally, we measured low-lying phonon dispersion branches and elastic constants in applied magnetic fields aimed to characterize the magnetoelastic coupling.",0906.3622v1 2010-05-26,Correlation between Local Structure Distortions and Martensitic Transformation in Ni-Mn-In alloys,"The local structural distortions arising as a consequence of increasing Mn content in Ni_2Mn_1+xIn_1-x (x=0, 0.3, 0.4, 0.5 and 0.6) and its effect on martensitic transformation have been studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni and Mn K-edges in the above compositions, the changes associated with respect to the local structure of these absorbing atoms are compared. It is seen that in the alloys exhibiting martensitic transformation ($x \ge 0.4$) there is a significant difference between the Ni-In and Ni-Mn bond lengths even in the austenitic phase indicating atomic volume to be the main factor in inducing martensitic transformation in Ni-Mn-In Heusler alloys.",1005.4873v1 2012-12-03,Role of covalent hybridization in martensitic structure and magnetic properties of shape memory alloys: the case of Ni50Mn5+xGa35-xCu10,"We have investigated the impact of covalent hybridization on martensitic structure and magnetic properties of Ni50Mn5+xGa35-xCu10 shape memory alloys. We found that the lattice distortion ((c-a)/a) of L10 martensite monotonously changes with the substitution of Mn for Ga atoms and shows a kink behavior at Ga(at.%)= 25 due to the weakened covalent effect between main-group and transition-metal atoms. Moreover, owing to the competition between covalence hybridization and magnetic ordering of introduced Mn atoms, the molecular magnetic moment and Curie temperature coincidently show maximums at Ga(at.%)=25 as well. These behaviors are closely associated with corresponding changes of the strength of covalent hybridization. The results therefore suggest that careful control of the concentration of main-group atoms in Heusler alloys can serve as an additional general tuning parameter for searching new multifunctional materials.",1212.0302v1 2014-03-28,First-principle prediction of Martensitic transformation and magnetic properties of Heusler-type Pt2-xMn1+xGa alloys,"The electronic structure, magnetism and phase stability of Pt2-xMn1+xGa(x=0, 0.25, 0.5, 0.75, 1) alloys are studied by first-principle calculations. The calculations reveal that a potential magnetic martensitic transformation can be expected in all the series. In addition, a large magnetic-field-induced strain is likely to appear in Pt2-xMn1+xGa(x=0, 0.25, 0.75, 1) alloys. The electronic structure calculations indicate that the tetragonal phase is stabilized upon the distortion because of the pseudogap formation at the Fermi Level. The magnetic structure is also investigated and the total magnetic moment of the tetragonal phase is a little larger than that of the cubic austenite phase in all the series.",1403.7318v3 2014-04-27,Magnetic shape memory microactuator,"Bimetallic composite nanotweezers based on Ti2NiCu alloy with shape memory effect (SME) have recently demonstrated the ability to manipulate real nano-objects, such as nanotubes, and bionanoparticles when heated to 40-60 C by laser radiation. The possibility of developing nanotweezers operating at constant temperature is of particular importance mainly for the manipulation of biological objects. In this work, a microactuator was produced using a composite bilayer made of a layer of rapidly quenched Ni53Mn24Ga23 ferromagnetic shape memory Heusler alloy and an elastic layer of Pt. The size of the microactuator is 25x2.3x1.7 micro-meters3. A controlled bending deformation of the actuator of 1.2 %, with a deflection of the end of the actuator higher than 2 micro-meter was obtained by applying a magnetic field of 8 T at T = 62 C. The possibility of the development of new technologies for magnetic-field-controlled nanotools operating at a constant temperature using the new multifunction magnetic shape memory alloys will be discussed.",1404.6762v1 2017-12-13,Co$_{2}$PtGa: A promising magnetic shape memory alloy with high martensite transition temperature,"In the present work, a combined theoretical and experimental study on Co$_{2}$PtGa Heusler alloy shows that it exhibits a martensite transition around 1320 K with a small thermal hysteresis (10 K). Dynamical stability of Co$_2$PtGa in the tetragonal phase has been established by the theoretically calculated phonon dispersion curves. Magnetization measurements suggest that this alloy is a ferromagnetic material with a saturation magnetic moment of 2.83 $\mu_B$/f.u. at 2 K, which is in excellent agreement with the value obtained from \textit{ab-initio} calculations (2.87 $\mu_B$/f.u.). Our present study demonstrates that Co$_{2}$PtGa is a promising material for high temperature magnetic shape memory application.",1712.04765v4 2020-08-27,Lattice strain accommodation and absence of pre-transition phases in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$,"The stoichiometric Ni$_{50}$Mn$_{25}$In$_{25}$ Heusler alloy transforms from a stable ferromagnetic austenitic ground state to an incommensurate modulated martensitic ground state with a progressive replacement of In with Mn without any pre-transition phases. The absence of pre-transition phases like strain glass in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$ alloys is explained to be the ability of the ferromagnetic cubic structure to accommodate the lattice strain caused by atomic size differences of In and Mn atoms. Beyond the critical value of $x$ = 8.75, the alloys undergo martensitic transformation despite the formation of ferromagnetic and antiferromagnetic clusters and the appearance of a super spin glass state.",2008.11982v1 2019-12-08,Investigation of Thermoelectric properties of Magnetic Insulator FeRuTiSi Using First Principle Calculation,"In this work, we have investigated the electronic structure and thermoelectric properties of quaternary heusler alloy, FeRuTiSi, using first principle DFT tools implemented in WIEN2k and BoltzTraP code. Electronic structure calculations using TB-mBJ potential shows appearance of flat band at the conduction band edge, thus electron in conduction band have the large effective mass (me*), and therefore mainly contribute for negatively large value of Seebeck coefficient (S). This alloy has indirect band gap of 0.59 eV, and shows the n-type transport behavior. Under the constant relaxation time approximation (tau = 10 -14 s), temperature dependent Seebeck coefficient, electrical conductivity (sigma), and electronic thermal conductivity (ke) were also estimated. The maximum figure-of-merit (ZT), for the FeRuTiSi compound is found to be ~0.86 at 840 K, with n-type doping, which suggests that this quaternary alloy can be a good candidate among the n-type material for thermoelectric applications in high-temperature reg",1912.03708v1 2022-01-31,Disorder-mediated quenching of magnetization in NbVTiAl: Theory and Experiment,"In this paper, we present the structural, electronic, magnetic and transport properties of a equiatomic quaternary alloy NbVTiAl. The absence of (111) and (200) peaks in X-ray diffraction (XRD) data confirms the A2-type structure. Magnetization measurements indicate a high Curie temperature and a negligibly small magnetic moment ($\sim 10^{-3} \mu_B/f.u.$) These observations are indicative of fully compensated ferrimagnetism in the alloy. Temperature-dependent resistivity indicates metallic nature. Ab-initio calculation of fully ordered NbVTiAl structure confirms a nearly half metallic behavior with a high spin polarization ($\sim$ 90 \%) and a net magnetic moment of 0.8 $\mu_B/f.u.$ (in complete contrast to the experimental observation). One of the main objective of the present paper is to resolve and explain the long-standing discrepancy between theoretical prediction and experimental observation of magnetization for V-based quaternary Heusler alloys, in general. To gain an in-depth understanding, we modelled various disordered states and its subsequent effect on the magnetic and electronic properties. The discrepancy is attributed to the A2 disorder present in the system, as confirmed by our XRD data. The presence of disorder also causes the emergence of finite states at the Fermi level, which impacts the spin polarization of the system.",2201.13037v1 2015-12-24,"Importance of spin-orbit coupling in power factor calculations for half-Heusler ANiB (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi)","We investigate the spin-orbit coupling (SOC) effects on the electronic structures and semi-classic transport coefficients of half-Heusler $\mathrm{ANiB}$ (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi) by using generalized gradient approximation (GGA). Calculated results show that SOC splits the valence bands at high symmetry $\Gamma$ point, and modifies the outline of $\Gamma$-centered valence bands, which has remarkable effects on the electron transport properties. Thermoelectric properties are performed through solving Boltzmann transport equations within the constant scattering time approximation. It is found that the compounds containing Sn atom have larger power factor in p-type doping than ones in n-type doping, and it is just the opposite for compounds containing Sb and Bi elements. The SOC has obvious detrimental influence on power factor in p-type doping, while has a negligible effect in n-type doping. These can be understood by considering the effects of SOC on the valence bands and conduction bands. The maximum power factors (MPF) are extracted in n-type and p-type doping with GGA and GGA+SOC, and the MPF at 300 K with SOC is predicted to be about 4.25\%$\sim$44.13\% smaller than that without SOC in the case of p-type doping for $\mathrm{ANiB}$ (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi). Therefore, it is crucial to consider SOC effects for theoretical analysis in the case of p-type doping in half-Heusler compounds composed of heavy elements.",1512.07710v1 2017-08-03,"A comparative study of different exchange-correlation functionals in understanding structural, electronic and thermoelectric properties of Fe$_{2}$VAl and Fe$_{2}$TiSn compounds","Fe$_{2}$VAl and Fe$_{2}$TiSn are full Heusler compounds with non-magnetic ground state. The two compouds are good thermoelectric materials. PBE and LDA(PW92) are the two most commonly used density functionals to study the Heusler compounds. Along with these two well studied exchange-correlation functionals, recently developed PBEsol, mBJ and SCAN functionals are employed to study the two compounds. Using the five functionals equilibrium lattice parameter and bulk modulus are calculated. Obtained values are compared with experimental reports wherever available. Electronic structure properties are studied by calculating dispersion curves, total and partial density of states. For Fe$_{2}$VAl, band gap of 0.22 eV is obtained from the mBJ potential which is in reasonable agreement with experimental value while, for Fe$_{2}$TiSn band gap of 0.68 eV is obtained. Fe$_{2}$VAl is predicted to be semimetallic with different values of negative gaps from LDA,PBEsol,PBE and SCAN functionals. Whereas, Fe$_{2}$TiSn is found to be semimetallic(semiconducting) from LDA,PBEsol(PBE,SCAN) functionals employed calculations. From the dispersion curve effective mass values are also computed to see the contribution to the Seebeck coefficient. In Fe$_{2}$TiSn, a flat band is present along the $\Gamma$-X direction with calculated value of effective mass $\sim$36 more than the mass of electron. The improvements or inadequacies among the functionals in explaining the properties of full Heusler alloys for thermoelectric application are thus observed through this study.",1708.01180v1 2020-08-31,Robust topological Hall effect driven by tunable noncoplanar magnetic state in Mn-Pt-In inverse tetragonal Heusler alloys,"Manipulation of magnetic ground states by effective control of competing magnetic interactions has led to the finding of many exotic magnetic states. In this direction, the tetragonal Heusler compounds consisting of multiple magnetic sublattices and crystal symmetry favoring chiral Dzyaloshinskii-Moriya interaction (DMI) provide an ideal base to realize non-trivial magnetic structures. Here, we present the observation of a large robust topological Hall effect (THE) in the multi-sublattice Mn$_{2-x}$PtIn Heusler magnets. The topological Hall resistivity, which originates from the non-vanishing real space Berry curvature in the presence of non-zero scalar spin chirality, systematically decreases with decreasing the magnitude of the canting angle of the magnetic moments at different sublattices. With help of first principle calculations, magnetic and neutron diffraction measurements, we establish that the presence of a tunable non-coplanar magnetic structure arising from the competing Heisenberg exchanges and chiral DMI from the D$_{2d}$ symmetry structure is responsible for the observed THE. The robustness of the THE with respect to the degree of non-collinearity adds up a new degree of freedom for designing THE based spintronic devices.",2008.13505v1 2017-10-05,"First-principles investigation of competing magnetic interactions in (Mn,Fe)Ru$_2$Sn Heusler solid solutions","Many Heusler compounds possess magnetic properties well-suited for applications as spintronic materials. The pseudo-binary Mn$_{0.5}$Fe$_{0.5}$Ru$_2$Sn, formed as a solid solution of two full Heuslers, has recently been shown to exhibit exchange hardening suggestive of two magnetic phases, despite existing as a \textit{single} chemical phase. We have performed a first-principles study of the chemical and magnetic degrees of freedom in the Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn pseudo-binary to determine the origin of the unique magnetic behavior responsible for exchange hardening within a single phase. We find a transition from antiferromagnetic (AFM) to ferromagnetic (FM) behavior upon replacement of Mn with Fe, consistent with experimental results. The lowest energy orderings in Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn consist of chemically- and magnetically-uniform (111) planes, with Fe-rich regions preferring FM ordering and Mn-rich regions preferring AFM ordering, independent of the overall composition. Analysis of the electronic structure suggests that the magnetic behavior of this alloy arises from a competition between AFM-favoring Sn-mediated superexchange and FM-favoring RKKY exchange mediated by spin-polarized conduction electrons. Changes in valency upon replacement of Mn with Fe shifts the balance from superexchange-dominated interactions to RKKY-dominated interactions.",1710.02089v1 2006-11-17,"Ab initio prediction of half-metallic properties for the ferromagnetic Heusler alloys Co$_2$MSi (M=Ti, V, Cr)","By means of density functional calculations the magnetic and electronic properties and phase stabilities of the Heusler compounds Co$_2$MSi (with M=Ti, V, Cr, Mn, Fe, Co, Ni) were investigated. Based on the calculated results we predict the ferromagnetic phases of the compounds Co$_2$TiSi, Co$_2$VSi and Co$_2$CrSi to be half-metals. Of particular interest is Co$_2$CrSi because of its high density of majority spin states at Fermi energy in combination with a reasonably high estimated Curie temperature of 747K. The compounds Co$_2$TiSi and Co$_2$VSi are thermodynamically stable, whereas Co$_2$CrSi is a metastable phase which might be stabilized by suitable experimental techniques.",0611466v1 2006-12-10,Substituting the main group element in cobalt - iron based Heusler alloys: Co$_2$FeAl$_{1-x}$Si$_x$,"This work reports about electronic structure calculations for the Heusler compound Co$_2$FeAl$_{1-x}$Si$_x$. Particular emphasis was put on the role of the main group element in this compound. The substitution of Al by Si leads to an increase of the number of valence electrons with increasing Si content and may be seen as electron-doping. Self-consistent electronic structure calculations were performed to investigate the consequences of the electron doping for the magnetic properties. The series Co$_2$FeAl$_{1-x}$Si$_x$ is found to exhibit half-metallic ferromagnetism and the magnetic moment follows the Slater-Pauling rule. It is shown that the electron-doping stabilises the gap in the minority states for $x=0.5$.",0612241v1 2007-06-25,Optical and magneto-optical properties of ferromagnetic full-Heusler films: experiments and first-principles calculations,"We report a joint theoretical and experimental study focused on understanding the optical and magneto-optical properties of Co-based full-Heusler compounds. We show that magneto-optical spectra calculated within ab-initio density functional theory are able to uniquely identify the features of the experimental spectra in terms of spin resolved electronic transitions. As expected for 3d-based magnets, we find that the largest Kerr rotation for these alloys is of the order of 0.3o in polar geometry. In addition, we demonstrate that (i) multilayered structures have to be carefully handled in the theoretical calculations in order to improve the agreement with experiments, and (ii) combined theoretical and experimental investigations constitute a powerful approach to designing new materials for magneto-optical and spin-related applications",0706.3613v1 2010-02-28,A new platform for topological quantum phenomena : Topological Insulator states in thermoelectric Heusler-related ternary compounds,"Topological insulators (TI) realize a novel state of quantum matter that are distinguished by topological invariants of bulk band structure rather than spontaneously broken symmetries. A number of exotic quantum phenomena have been predicted to exist in multiply-connected geometries which require an enormous amount of materials flexibility. We have extended our previous search for TI materials from binary (Bi2X3 series) to the thermoelectric ternary compounds. We discover that the distorted LuPtSb is the first ternary compound harboring a 3D topological insulator state. We also show that the half-Heusler LuPtSb-type series is a natural platform that hosts a range of candidate compounds, alloys and artificial heterostructures (quantum-wells). We also discovered several different paradigms of trivial and non-trivial topological ordering in this class, including a metallic nontrivial topological state in YAuPb. Some of these materials are grown (results will be reported separately).",1003.0155v1 2011-08-19,Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films,"This paper shows the correlation between chemical order, lattice strains and magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A detailed magnetic characterization has been performed using vector field magnetometery combined with numerical Stoner-Wohlfarth analysis. We demonstrate the presence of three types of in-plane anisotropies: one biaxial, as expected for the cubic symmetry, and other two uniaxial ones. The three anisotropies show different behavior with the annealing temperature. The biaxial anisotropy shows a monotonous increase. The uniaxial anisotropy, parallel with the hard biaxial axes, related to the chemical homogeneity, decreases, while the other, supposed to have magnetostatic origin, remains constant.",1108.4043v2 2013-06-26,Effective Scattering Cross-section in Lattice Thermal Conductivity Calculation with Differential Effective Medium Method,"To further reduce the lattice thermal conductivity of thermoelectric materials, the technique of embedding nano-inclusions into bulk matrix materials, in addition to point defect scattering via alloying, was widely applied. Differential Effective Medium (DEM) method was employed to calculate two-phase heterogeneous systems. However, in most effective medium treatment, the interface scattering of matrix phonons by embedded nanoparticle was underestimated by adopting particle's projected area as scattering cross-section. Herein, modified cross-section calculations, as well as grain sizes dispersions, are applied in DEM, with the calculations then validated by comparing with Monte-Carlo simulations and existing experimental data. Predictions of lattice thermal conductivity reduction on in-situ formed Full Heusler(FH)/Half Heusler(HH) nano/matrix system are discussed.",1306.6274v1 2014-04-22,First principles investigation of magnetocrystalline anisotropy at the L2$_1$ Full Heusler|MgO interfaces and tunnel junctions,"Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been studied using first principles calculations. It is found that Co terminated Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31 mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic anisotropy. Atomic layer resolved analysis indicates that the origin of perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be attributed to the out-of-plane orbital contributions of interfacial Co atoms. At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to favor in-plane magnetic anisotropy for all terminations.",1404.5646v2 2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic resonance (FMR) measurements and calculations from first principles to investigate how the composition of the epitaxially grown NiMnSb influences the magnetodynamic properties of saturation magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$. $M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while the Gilbert damping is minimum. We find excellent quantitative agreement between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows the same trend as the experimental data, but has a larger magnitude. Additionally to the unique in-plane anisotropy of the material, these tunabilities of the magnetodynamic properties can be taken advantage of when employing NiMnSb films in magnonic devices.",1510.01894v1 2016-07-19,Lattice Thermal Conductivity of NiTiSn Half-Heusler Thermoelectric Materials from First-Principles Calculations,"The microscopic physics behind the lattice thermal conductivity of NiTiSn is investigated using first-principles-based anharmonic lattice dynamics. The calcu lated lattice thermal conductivity of bulk materials (5.3 W/m.K) is in good agreement with the experimental value at the optimal working temper ature (700 K), but is overestimated below this temperature. The calculated values can be strongly affected by the size of the crystalline grains. We show tha t the lattice thermal conductivity is dominated by the acoustic (transverse and mostly longitudinal) modes with no contribution from the optical modes. The a coustic phonons are located below 150 cm-1 and involve mainly the tin atoms. The calculated mean free path of the most heat carrying phonons is around f ifty nanometers with a maximum life time of approx. 100 ps. These theoretical results are a step forward in developing the experimental design of low thermal conductivity NiTiSn Heusler based materials.",1607.05558v1 2016-10-09,Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure,"The thermoelectric properties of n type semiconductor, TiNiSn is optimized by partial substitution with metallic, MnNiSb in the half Heusler structure. Herein, we study the transport properties and intrinsic phase separation in the system. The Ti1-xMnxNiSn1-xSbx alloys were prepared by arc-melting and were annealed at temperatures obtained from differential thermal analysis and differential scanning calorimetry results. The phases were characterized using powder X-ray diffraction patterns, energy dispersive X-ray spectroscopy, and differential scanning calorimetry. After annealing the majority phase was TiNiSn with some Ni rich sites and the minority phases was majorly Ti6Sn5, Sn, and MnSn2. Ni rich sites were caused by Frenkel defects, this led to a metal-like behavior of the semiconducting specimens at low temperature. For x up to 0.05 the samples showed an activated conduction, whereas for x>0.05 they showed metallic character. The figure of merit for x=0.05 was increased by 61% (ZT=0.45) in comparison to the pure TiNiSn.",1610.02657v1 2017-08-16,Ab-initio design of new Heusler materials for thermoelectric applications,"In search of new prospects for thermoelectric materials, using ab-initio calculations and semi-classical Boltzmann theory, we have systematically investigated the electronic structure and transport properties of 18-valence electron count cobalt based half-Heusler alloys with prime focus on CoVSn, CoNbSn, CoTaSn, CoMoIn, and CoWIn. The effect of doping on transport properties has been studied under the rigid band approximation. The maximum power factor, S$^2\sigma$, for all systems is obtained on hole doping and is comparable to the existing thermoelectric material CoTiSb. The stability of all the systems is verified by phonon calculations. Based on our calculations, we suggest that CoVSn, CoNbSn, CoTaSn, CoMoIn and CoWIn could be potential candidates for high temperature thermoelectric materials.",1708.04768v1 2018-01-26,Stoichiometric and off-stoichiometric full Heusler $\mathbf {Fe_2V_{1-x}W_xAl} $ thermoelectric systems,"A series of full-Heusler alloys, $\rm Fe_2V_{1-x}W_xAl$, $0 \leq x \leq 0.2$, was prepared, characterized and relevant physical properties to account for the thermoelectric performance were studied in a wide temperature range. Additionally, off-stoichiometric samples with similar compositions have been included, and a 10~\% improvement of the thermoelectric figure of merit was obtained. The V/W substitution causes i) a change of the main carrier type, from holes to electrons as evidenced from Seebeck and Hall measurements and ii) a substantial reduction of the lattice thermal conductivity due to a creation of lattice disorder by means of a distinct different mass and metallic radius upon the V/W substitution. Moreover $ZT$ values above 0.2 have been obtained. A microscopic understanding of the experimental data observed is revealed from ab-initio calculations of the electronic and phononic structure.",1801.08966v2 2018-05-07,High-temperature thermoelectric properties of half-Heusler phases Er$_{1-x}$Ho$_x$NiSb,"Polycrystalline samples of Er$_{1-x}$Ho$_x$NiSb ($x$ = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and optical metallography. The results proved the formation of half-Heusler alloys in the entire composition range. Their electrical transport properties (resistivity, thermoelectric power) were studied in the temperature interval 350-1000 K. The measured electrical resistivity spanned between 5 and 25 $\mu \Omega$m. The maximum thermopower of 50-65 $\mu$V/K was observed at temperatures 500-650 K. Replacing Ho for Er resulted in a non-monotonous variation of the thermoelectric power factor ($PF = S^2/\rho$). The largest $PF$ of 4.6 $\mu$WcmK$^{-2}$ was found at 660 K for Er$_{0.5}$Ho$_{0.5}$NiSb. This value is distinctly larger than PF determined for the terminal phases ErNiSb and HoNiSb.",1805.02435v1 2018-08-08,High throughput screening for spin-gapless semiconductors in quaternary Heusler compounds,"Based on high throughput density functional theory calculations, we performed systematic screening for spin-gapless semiconductors (SGSs) in quaternary Heusler alloys XX 0 YZ (X, X 0 , and Y are transition metal elements without Tc, and Z is one of B, Al, Ga, In, Si, Ge, Sn, Pb, P, As, Sb, and Bi). Following the empirical rule, we focused on compounds with 21, 26, or 28 valence electrons, resulting in 12, 000 possible chemical compositions. After systematically evaluating the thermodynamic, mechanical, and dynamical stabilities, we successfully identified 70 stable SGSs, confirmed by explicit electronic structure calculations with proper magnetic ground states. It is demonstrated that all four types of SGSs can be realized, defined based on the spin characters of the bands around the Fermi energy, and the type-II SGSs show promising transport properties for spintronic applications. The effect of spin-orbit coupling is investigated, resulting in large anisotropic magnetoresistance and anomalous Nernst effects.",1808.02684v1 2018-12-20,"Theoretical study of the structural stability, electronic and magnetic properties of XVSb (X $=$ Fe, Ni, and Co) half-Heusler compounds","The structural, electronic and magnetic properties of half-Heusler compounds XVSb (X $=$ Fe, Co and Ni) are investigated by using the density functional theory with generalized gradient approximation (GGA), and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential approximation. It is found that the half-metallic gaps are generally reasonably widened by mBJ as compared to the GGA approximation. The magnetic proprieties of XVSb (X $=$ Fe, Co and Ni) are well defined within mBJ with an exact integer value of magnetic moment. The band gaps given by TB-mBJ are in good agreement with the available theoretical data. The FeVSb exhibits a semiconductor nature. The CoVSb and NiVSb present half-metallic behaviour with total magnetic moment of $1\mu_\text{B}$ and $2\mu_\text{B}$ in good agreement with Slater-Pauling rule. These alloys seem to be a potential candidate of spintronic devices.",1812.08559v1 2019-05-23,"Thermodynamic and Thermoelectric Properties of CoFeYGe (Y= Ti, Cr) Quaternary Heusler Alloys: First Principle Calculations","Utilizing a material in thermoelectric applications requires a mechanical, thermal, and lattice stability as well a high figure of merit (ZT). In this work, we present the structural, electronic, magnetic, mechanical, thermodynamic, dynamic, and thermoelectric properties of CoFeYGe (Y = Ti, Cr) quaternary Heusler compounds using the density functional theory (DFT). The calculated mechanical properties and phonon dispersions reveal that the structures of these compounds are stable. Both CoFeCrGe and CoFeTiGe compounds show a ferromagnetic and ferrimagnetic half-metallic behavior with band gaps of 0.41 and 0.38 eV, respectively. The lattice thermal conductivity (\k{appa}L) exhibits low values that reach 3.01 W/(m.K) (3.47 W/(m.K)) for CoFeCrGe (CoFeTiGe) at 1100 K. The optical phonon modes have a large contribution of 60.2% (70.9 %) to \k{appa}L value for CoFeCrGe (CoFeTiGe). High ZT values of 0.71 and 0.65 were obtained for CoFeCrGe and CoFeTiGe, respectively. Based on our calculations, CoFeCrGe and CoFeTiGe combine both good spintronic and thermoelectric behaviors that may be used in spin injection applications.",1905.09854v1 2020-09-02,"Phase transition in the magnetocrystalline anisotropy of tetragonal Heusler alloys: Rh$_2T$Sb, $T=$ Fe, Co","This work reports on first principles calculations of the electronic and magnetic structure of tetragonal Heusler compounds with the composition Rh$_2$Fe$_{x}$Co$_{1-x}$Sb ($0\leq x\leq1$). It is found that the magnetic moments increase from 2 to 3.4~$\mu_B$ and the Curie temperature decreases from 500 to 464~K with increasing Fe content $x$. The $3d$ transition metals make the main contribution to the magnetic moments, whereas Rh contributes only approximately 0.2~$\mu_B$ per atom, independent of the composition. The paper focuses on the magnetocrystalline anisotropy of the borderline compounds Rh$_2$FeSb, Rh$_2$Fe$_{0.5}$Co$_{0.5}$Sb, and Rh$_2$CoSb. A transition from easy-axis to easy-plane anisotropy is observed when the composition changes from Rh$_2$CoSb to Rh$_2$FeSb. The transition occurs at an iron concentration of approximately 40\%.",2009.00920v1 2021-02-23,Strain glass versus antisite disorder induced ferromagnetic state in Fe doped Ni-Mn-In Heusler martensites,"Fe doping in Ni$_2$Mn$_{1.5}$In$_{0.5}$ results in suppression of the martensitic phase via two contrasting routes. In Ni$_2$Mn$_{1.5-x}$Fe$_{x}$In$_{0.5}$, the martensitic phase is converted to a strain glassy phase, while in Ni$_{2-y}$Fe$_y$Mn$_{1.5}$In$_{0.5}$, a cubic ferromagnetic phase results at the expense of the martensite. Careful studies of magnetic and structural properties reveal the presence of the impurity $\gamma -$(Fe,Ni) phase as the reason for the emergence of non-ergodic strain glassy phase when Fe is sought to be doped at Y/Z (Mn) sites of X$_2$YZ Heusler alloy. Whereas attempts to dope Fe in the X (Ni) sublattice result in an A2 type antisite disorder that promotes a ferromagnetic ground state.",2102.11611v1 2023-04-06,Formation of Core-Shell Precipitates in off-stochiometric Ni-Mn-Sn Heusler alloys probed through the induced Sn-moment,"The Shell-ferromagnetic effect originates from the segregation process in off-stochiometric Ni-Mn-based Heusler. In this work, we investigate the precipitation process of L2$_1$-ordered Ni$_2$MnSn and L1$_0$-ordered NiMn in off-stochiometric Ni$_{50}$Mn$_{45}$Sn$_{5}$ during temper annealing, by X-ray diffraction (XRD) and $^{119}$Sn M\""ossbauer spectroscopy. While XRD probes long-range ordering of the lattice structure, M\""ossbauer spectroscopy probes nearest-neighbour interactions, reflected in the induced Sn magnetic moment. As shown in this work, the induced magnetic Sn moment can be used as a detector for microscopic structural changes and is, therefore, a powerful tool for investigating the formation of nano-precipitates. Similar research can be performed in the future, for example, on different pinning type magnets like Sm-Co or Nd-Fe-B.",2304.03033v1 2002-09-24,Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni2.19Mn0.81Ga Heusler alloy,"In this paper we report the existence of a giant magnetocaloric effect (MCE) in a intermetallic compound non-containing rare-earth. This effect is associated with the concomitant occurrence of a structural and a magnetic transition. The result has been compared with that obtained in a parent compound in which magnetic and structural transition occur separately.",0209564v2 2003-08-07,The effect of the spin-orbit interaction on the band gap of half-metals,"The spin-orbit interaction can cause a nonvanishing density of states (DOS) within the minority-spin band gap of half-metals around the Fermi level. We examine the magnitude of the effect in Heusler alloys, zinc-blende half metals and diluted magnetic semiconductors, using first-principles calculations. We find that the ratio of spin-down to spin-up DOS at the Fermi level can range from below 1% (e.g. 0.5% for NiMnSb) over several percents (4.2% for (Ga,Mn)As) to 13% for MnBi.",0308146v1 2006-03-10,Model Hamiltonian parameters for half-metallic ferromagnets NiMnSb and CrO2,"Using the recently developed Nth-order muffin-tin-orbital (NMTO) based downfolding technique we revisit the electronic properties of half-metallic ferromagnets, the semi-Heusler NiMnSb and rutile CrO2. The NMTO Wannier orbitals for the Mn-d and Cr-t2g manifolds are constructed and the mechanism of chemical bonding is discussed. The effective hopping Hamiltonian parameters are calculated using a NMTO downfolded basis set. We propose model Hamiltonian parameters with possibly minimal basis sets for both half-metallic ferromagnetic alloys.",0603305v2 2007-11-28,Tailoring magnetic and magnetocaloric properties of martensitic transitions in ferromagnetic Heusler alloys,"Ni$_{50}$Mn$_{34}$In$_{16}$ undergoes a martensitic transformation around 250 K and exhibits a field induced reverse martensitic transformation and substantial magnetocaloric effects. We substitute small amounts Ga for In, which are isoelectronic, to carry these technically important properties to close to room temperature by shifting the martensitic transformation temperature.",0711.4506v1 2009-02-18,Majority-spin non-quasiparticle states in half-metallic ferrimagnet Mn$_2$VAl,"The density of non-quasiparticle states in the ferrimagnetic full-Heuslers Mn$_2$VAl alloy is calculated from first principles upon appropriate inclusion of correlations. In contrast to most half-metallic compounds, this material displays an energy gap in the majority-spin spectrum. For this situation, non-quasiparticle states are located below the Fermi level, and should be detectable by spin-polarized photoemission. This opens a new way to study many-body effects in spintronic-related materials.",0902.3109v1 2009-06-04,Giant diamagnetism in half-metallic Co$_{2}$CrAl Heusler alloy,"A giant diamagnetism in the Co$_{2}$CrAl compounds, in both bulk and thin film, below a certain temperature ($T_z$) was observed. Above $T_z$, the compound behaves as an ordinary ferromagnet. The diamagnetic alignment might be initiated by the Landau diamagnetism because of the half-metallic properties and the pinning of the diamagnetism is preserved by the peculiar electronic structures.",0906.0824v1 2010-01-04,Rare-earth impurities in Co$_2$MnSi: an opportunity to improve Half-Metallicity at finite temperatures,"We analyse the effects of doping Holmium impurities into the full-Heusler ferromagnetic alloy Co$_2$MnSi. Experimental results, as well as theoretical calculations within Density Functional Theory in the ""Local Density Approximation plus Hubbard U"" framework show that the holmium moment is aligned antiparallely to that of the transition metal atoms. According to the electronic structure calculations, substituting Ho on Co sites introduces a finite density of states in the minority spin gap, while substitution on the Mn sites preserves the half-metallic character.",1001.0480v1 2011-12-09,Spin polarized tunneling in MgO-based tunnel junctions with superconducting electrodes,"We prepared magnetic tunnel junctions with one ferromagnetic and one superconducting Al-Si electrode. Pure cobalt electrodes were compared with a Co-Fe-B alloy and the Heusler compound Co2FeAl. The polarization of the tunneling electrons was determined using the Maki-Fulde-model and is discussed along with the spin-orbit scattering and the total pair-breaking parameters. The junctions were post-annealed at different temperatures to investigate the symmetry filtering mechanism responsible for the giant tunneling magnetoresistance ratios in Co-Fe-B/ MgO/ Co-Fe-B junctions.",1112.2110v1 2012-10-27,"Structural, magnetic, magnetocaloric and magneto-transport properties in Ge doped Ni-Mn-Sb Heusler Alloys","The effect of Ge substitution on the magnetic, magnetocaloric and transport properties of Ni45Co5Mn38Sb12-xGex (x=0-3) has been investigated. The decrease in the exchange interaction brought by Ge substitution can be seen from the reduction in the magnetization of austenite phase and the increase in the martensitic transition temperature. Large magnetocaloric effect and magnetoresistance have been observed at room temperature, making it a potential material system for various applications.",1210.7297v2 2014-01-08,Tri-Dirac Surface Modes in Topological Superconductors,"We propose a new type of topological surface modes having cubic dispersion in three-dimensional topological superconductors. Lower order dispersions are prohibited by the threefold rotational symmetry and time-reversal symmetry. Cooper pairing in the bulk changes sign under improper rotations, akin to$^{3}$He-B. The surface manifestations are a divergent surface density of states at the Fermi level and isospins that rotate three times as they circle the origin in momentum space. We propose that Heusler alloys with band inversion are candidate materials to harbor the novel topological superconductivity.",1401.1823v1 2014-09-24,Direct magnetocaloric effect measurement technique in alternating magnetic fields,"A method for direct measurement of the magnetocaloric effect (MCE) in alternating magnetic fields is offered. Main advantages of the method compared to a classical direct one are the high temperature sensitivity (better than 10-3 K); the ability of measuring of MCE in weak magnetic fields (by several tens oersteds and higher); the ability of measuring of MCE on small-sized samples (1x1x 0.01 mm3 and larger); the ability of measuring of MCE in alternating magnetic fields up to 50 Hz of frequency. The results on measurement of MCE on Gd and Ni-Mn-In Heusler alloy are reported.",1409.6898v1 2016-02-01,Anti-sites disordering suppression of the possible phase transition in Mn2CrGa,"Theoretical and experimental characterizations of Mn2CrGa compound in regard to the possibility of phase transformation have been carried out in this work. Under a high ordering L21 structure, this compound has the potential to be a martensite phase transition material. However, experimental results show a severe disordering took place in this system, which forbids the occurring of the phase transition. This work provides important reference for the design of new phase transition materials in Heusler alloys.",1602.00397v1 2016-11-16,Perpendicular magnetic anisotropy in Co$_2$MnGa,"We report perpendicular magnetic anisotropy in the ferromagnetic Heusler alloy Co$_2$MnGa in a MgO/Co$_2$MnGa/Pd trilayer stack for Co$_2$MnGa thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin reorientation transition from perpendicular to in-plane magnetic anisotropy which we study through the anomalous Hall effect. From the temperature dependence of the anomalous Hall effect, we observe the expected scaling of $\rho_{xy}^{AHE}$ with $\rho_{xx}$, suggesting the intrinsic and side-jump mechanisms are largely responsible for the anomalous Hall effect in this material.",1611.05110v1 2017-07-26,Interfacial exchange interactions and magnetism of Ni2MnAl/Fe bilayers,"Based on a multi-scale calculations, combining ab-initio methods with spin dynamics simulations, we perform a detailed study of the magnetic behavior of Ni2MnAl/Fe bilayers. Our simulations show that such a bilayer exhibits a small exchange bias effect when the Ni2MnAl Heusler alloy is in a disordered B2 phase. Additionally, we present an effective way to control the magnetic structure of the Ni2MnAl antiferromagnet, in the pseudo-ordered B2-I as well as the disordered B2 phases, via a spin-flop coupling to the Fe layer.",1707.08651v1 2019-10-29,Possible martensitic transformation in Pd2MnTi and Pt2MnTi: First-principles investigation,"The martensitic transformation in new-type all-d-metal Heusler alloys Pd2MnTi and Pt2MnTi have been investigated based on first-principles investigations. The calculated results indicate that the martenstic transformation have great possibility to occur in both Pd2MnTi and Pt2MnTi. The energy differences between the cubic and tetragonal phases are 215.12 meV and 329.45 meV for Pd2MnTi and Pt2MnTi, respectively. The analysis of the electronic structure of cubic and tetragonal phases also support this conclusion. The magnetic properties are also investigated for the two compounds.",1910.13075v1 2016-03-13,Perpendicular magnetic anisotropy in Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si,"We report perpendicular magnetic anisotropy (PMA) in the half-metallic ferromagnetic Heusler alloy Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS) in a MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2 nm, with a magnetic anisotropy energy density of $K_U = 1.5\times 10^6$ erg/cm$^3$ for t$_{\tiny \textrm{CFMS}} = 1.5$ nm. Both the MgO and Pd layer are necessary to induce the PMA. We measure a tunable anomalous Hall effect, where its sign and magnitude vary with both the CFMS and Pd thickness.",1603.04072v1 2019-03-26,Quantum topological transitions and spinons in metallic ferro- and antiferromagnets,"An effective Hamiltonian describing fluctuation effects in the magnetic phases of the Hubbard model in terms of spinon excitations is derived. A comparison of spin-rotational Kotliar-Ruckenstein slave boson and Ribeiro-Wen dopon representations is performed. The quantum transition into the half-metallic ferromagnetic state with vanishing of spin-down Fermi surface is treated as the topological Lifshitz transition in the quasimomentum space. The itinerant-localized magnetism transitions and Mott transition in antiferromagnetic state are considered in the topological context. Related metal-insulator transitions in Heusler alloys are discussed.",1903.11003v1 2022-12-15,Griffiths' phase behavior of the Weyl semimetal CrFeVGa,"We report a combined theoretical and experimental study of a new topological semimetal CrFeVGa with an emphasis on the role of atomic disorder on the magnetoelectronic properties and its applications.CrFeVGa belongs to the quaternary Heusler alloy family and crystallizes in the cubic structure. Synchrotron XRD measurement confirms B2 disorder, which plays a crucial role in dictating the electronic and magnetic properties of the system.",2212.07576v1 2023-09-29,Micromagnetics of ferromagnetic/antiferromagnetic nanocomposite materials. Part I: Towards the mesoscopic approach,"In the first of two articles, we present here a novel mesoscopic micromagnetic approach for simulating materials composed of ferromagnetic and antiferromagnetic phases. Starting with the atomistic modeling of quasi one-dimensional systems, we explicitly show how the material parameters for the mesoscopic model of an antiferromagnet can be derived. The comparison between magnetization profiles obtained in atomistic and mesoscopic calculations (using a Heusler alloy as an example) proves the validity of our method. This approach opens up the possibility to recover the details of the magnetization distribution in ferromagnetic/antiferromagnetic materials with the resolution of a few nanometers covering length scales up to several hundreds of nanometers.",2309.17131v1 2013-05-15,"Structural ordering driven anisotropic magnetoresistance, anomalous Hall resistance and its topological overtones in full-Heusler Co2MnSi thin films","We report the evolution of crystallographic structure, magnetic ordering and electronic transport in thin films of full-Heusler alloy Co$_2$MnSi deposited on (001) MgO with annealing temperatures ($T_A$). By increasing the $T_A$ from 300$^\circ$C to 600$^\circ$C, the film goes from a disordered nanocrystalline phase to $B2$ ordered and finally to the $L2_1$ ordered alloy. The saturation magnetic moment improves with structural ordering and approaches the Slater-Pauling value of $\approx 5.0 \mu_B$ per formula unit for $T_A$ = 600$^\circ$C. At this stage the films are soft magnets with coercive and saturation fields as low as $\approx$ 7 mT and 350 mT, respectively. Remarkable effects of improved structural order are also seen in longitudinal resistivity ($\rho_{xx}$) and residual resistivity ratio. A model based upon electronic transparency of grain boundaries illucidates the transition from a state of negative $d\rho/dT$ to positive $d\rho/dT$ with improved structural order. The Hall resistivity ($\rho_{xy}$) derives contribution from the normal scattering of charge carriers in external magnetic field, the anomalous effect originating from built-in magnetization and a small but distinct topological Hall effect in the disordered phase. The carrier concentration ($n$) and mobility ($\mu$) have been extracted from the high field $\rho_{xy}$ data. The highly ordered films are characterized by $n$ and $\mu$ of 1.19$\times$ 10$^{29}$ m$^{-3}$ and 0.4 cm$^2V^{-1}s^{-1}$ at room temperature. The dependence of $\rho_{xy}$ on $\rho_{xx}$ indicates the dominance of skew scattering in our films, which shows a monotonic drop on raising the $T_A$. The topological Hall effect is analyzed for the films annealed at 300$^\circ$C. ......",1305.3453v1 2014-08-02,Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates,"We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate. Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance (TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a switching layer. Using a thermal activation model, the intrinsic critical current density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lower than 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett. 100, 182403 (2012)]. We found that the Gilbert damping constant evaluated using ferromagnetic resonance measurements for the polycrystalline CFA film was ~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0 for the polycrystalline MTJ was mainly attributed to the low damping of the CFA layer compared with the value in the epitaxial one (~0.04).",1408.0341v1 2018-05-18,Reentrant cluster glass and stability of ferromagnetism in Ga2MnCo Heusler alloy,"We present here a detailed investigation into the magnetic ordering of full Heusler alloy Ga$_2$MnCo using dc, ac magnetization measurements, neutron diffraction and neutron depolarization experiments. Crystal structure at room temperature was first confirmed to be L2$_1$ using the highly intense synchrotron X-ray diffraction (XRD) technique. Temperature dependent magnetization reveals that Ga$_2$MnCo enters a ferromagnetic (FM) state at $T_C = $154 K, characterized by a sharp increase in magnetization and a plateau-like region hereafter. As the temperature is decreased further, a sharp drop in magnetization is observed at $T_f$ = 50 K, hinting towards an antiferromagnetic (AFM) phase change. Neutron diffraction (ND) recorded over the range of temperature from 6 to 300 K, provides combined information regarding crystal as well as magnetic structure. Accordingly, an increase in the intensity of the ND pattern is seen at 150 K, signaling onset of long range FM order. However, there is no sign of appearance of superlattice reflections corresponding to the AFM phase, in the patterns recorded below 50 K. An unusual discontinuity in the unit cell volume is seen around $T_f$ indicating a coupling of this second transition with the contraction of the lattice. Attempts to unravel this interesting magnetic behaviour using ac susceptibility measurements lead to the existence of glassy magnetism below $T_f$. Systematic analysis of the susceptibility results along with neutron depolarization measurement, identifies the low temperature phase as a reentrant cluster glass.",1805.07320v1 2019-11-15,Fermi level tuning and atomic ordering induced giant anomalous Nernst effect in Co2MnAl1-xSix Heusler alloy,"Co2MnAl has been predicted to have Weyl points near Fermi level which is expected to give rise to exotic transverse transport properties such as large anomalous Hall(AHE) and Nernst effects(ANE) due to large Berry curvature. In this study, the effect of Fermi level position and atomic ordering on AHE and ANE in Co2MnAl1-xSix were studied systematically. The Co2MnAl film keeps B2-disordred structure regardless of annealing temperature, which results in much smaller anomalous Hall conductivity sigma_xy and transverse Peltier coefficient sigma_xy than those calculated for L21-ordered Co2MnAl. Our newly performed calculation of sigma_xy with taking B2 disordering into account well reproduces experimental result, thus it was concluded that Berry curvature originating from Weyl points is largely reduced by B2 disordering. It was also revealed Al substitution with Si shifts the position of Fermi level and improves the L21-atomic ordering largely, leading to strong enhancement of sigma_xy, which also agreed with our theoretical calculation. The highest thermopower of ANE of 6.1uV, which is comparable to the recent reports for Co2MnGa, was observed for Co2MnAl0.63Si0.37 because of dominant contribution of sigma_xy. This study clearly shows the importance of both Fermi level tuning and high atomic ordering for obtaining the effect of topological feature in Co-based Heusler alloys on transverse transport properties.",1911.07741v1 2021-07-01,Dopant-segregation to grain boundaries controls electrical conductivity of n-type NbCo(Pt)Sn half-Heusler alloy mediating thermoelectric performance,"Science-driven design of future thermoelectric materials requires a deep understanding of the fundamental relationships between microstructure and transport properties. Grain boundaries in polycrystalline materials influence the thermoelectric performance through the scattering of phonons or the trapping of electrons due to space-charge effects. Yet, the current lack of careful investigations on grain boundary-associated features hinders further optimization of properties. Here, we study n-type NbCo1-xPtxSn half-Heusler alloys, which were synthesized by ball milling and spark plasma sintering (SPS). Post-SPS annealing was performed on one sample, leading to improved low-temperature electrical conductivity. The microstructure of both samples was examined by electron microscopy and atom probe tomography. The grain size increases from ~230 nm to ~2.38 {\mu}m upon annealing. Pt is found within grains and at grain boundaries, where it locally reduces the resistivity, as assessed by in situ four-point-probe electrical conductivity measurement. Our work showcases the correlation between microstructure and electrical conductivity, providing opportunities for future microstructural optimization by tuning the chemical composition at grain boundaries.",2107.00326v1 2018-10-17,"Investigation of the structural, electronic, transport and magnetic properties of Co$_2$FeGa Heusler alloy nanoparticles","We report the structural, transport, electronic, and magnetic properties of Co$_2$FeGa Heusler alloy nanoparticles. The Rietveld refinements of x-ray diffraction (XRD) data with the space group Fm$\bar {3}$m clearly demonstrates that the nanoparticles are of single phase. The particle size (D) decreases with increasing the SiO$_2$ concentration. The Bragg peak positions and the inter-planer spacing extracted from high-resolution transmission electron microscopy image and selected area electron diffraction are in well agreement with data obtained from XRD. The coercivity initially increases from 127~Oe to 208~Oe between D = 8.5~nm and 12.5~nm, following the D$^{-3/2}$ dependence and then decreases with further increasing D up to 21.5~nm with a D$^{-1}$ dependence, indicating the transition from single domain to multidomain regime. The effective magnetic anisotropic constant behaves similarly as coercivity, which confirms this transition. A complex scattering mechanisms have been fitted to explain the electronic transport properties of these nanoparticles. In addition we have studied core-level and valence band spectra using photoemission spectroscopy, which confirm the hybridization between $d$ states of Co/Fe. Further nanoparticle samples synthesized by co-precipitation method show higher saturation magnetization. The presence of Raman active modes can be associated with the high chemical ordering, which motivates for detailed temperature dependent structural investigation using synchrotron radiation and neutron sources.",1810.07660v1 2019-07-13,Magnetocaloric properties and critical behavior of Co$_2$Cr$_{1-x}$Mn$_x$Al Heusler alloys,"We study the magnetocaloric effect and critical behavior of Co$_2$Cr$_{1-x}$Mn$_x$Al ($x=$ 0.25, 0.5, 0.75) Heusler alloys across the ferromagnetic (FM) transition (T$_{\rm C}$). The Rietveld refinement of x-ray diffraction patterns exhibit single phase cubic structure for all the samples. The temperature dependent magnetic susceptibility $\chi$(T) data show a systematic enhancement in the Curie temperature and effective magnetic moment with Mn concentration, which is consistent with the Slater-Pauling behavior. The M(H) isotherms also exhibit the FM ordering and the analysis of $\chi$(T) data indicates the nature of the phase transition to be a second order, which is further supported by scaling of the entropy curves and Arrott plot. Interestingly, the Mn substitution causes an increase in the magnetic entropy change and hence large relative cooling power for multi-stage magnetic refrigerator applications. In order to understand the nature of the magnetic phase transition we examine the critical exponents $\beta$, $\gamma$, $\delta$ for the $x=$ 0.75 sample by the modified Arrott plot and the critical isotherm analysis, which is further confirmed by Kouvel-Fisher method and Widom scaling relation, respectively. The estimated values of $\beta=$ 0.507, $\gamma=$ 1.056, $\delta=$ 3.084 are found to be close to the mean field theoretical values. The renormalized isotherms (m vs h) corresponding to these exponent values collapse into two branches, above and below T$_{\rm C}$ that validates our analysis. Our results suggest for the existence of long-range FM interactions, which decays slower than power law as $J(r)\sim r^{-4.5}$ for a 3 dimensional mean field theory.",1907.06114v1 2019-10-16,Modeling magnetic evolution and exchange hardening in disordered magnets: The example of Mn$_{1-x}$Fe$_x$Ru$_2$Sn Heusler alloys,"We demonstrate how exchange hardening can arise in a chemically-disordered solid solution from a first-principles statistical mechanics approach. A general mixed-basis chemical and magnetic cluster expansion has been developed, and applied to the Mn$_{1-x}$Fe$_x$Ru$_2$Sn Heusler alloy system; single-phase solid solutions between antiferromagnetic \ch{MnRu2Sn} and ferromagnetic \ch{FeRu2Sn} with disorder on the Mn/Fe sublattice that exhibit unexpected exchange hardening. Monte Carlo simulations applied to the cluster expansion are able to reproduce the experimentally measured magnetic transition temperatures and the bulk magnetization as a function of composition. The magnetic ordering around a site is shown to be dependent not only on bulk composition, but also on the identity of the site and the local composition around that site. The simulations predict that local antiferromagnetic orderings form inside a bulk ferromagnetic region at intermediate compositions that drives the exchange hardening. Furthermore, the antiferromagnetic regions disorder at a lower temperature than the ferromagnetic regions, providing an atomistic explanation for the experimentally-observed decrease in exchange hardening with increasing temperature. These effects occur on a length scale too small to be resolved with previously-used characterization techniques.",1910.07543v1 2019-06-15,"Effect of L21 and XA ordering on phase stability, half-metallicity and magnetism of Co2FeAl Heusler Alloy: GGA and GGA+U approach","The generalized gradient approximation (GGA) scheme in the first-principles calculations are used to study the effect of L21 and XA ordering on the phase stability, half-metallicity and magnetism of Co2FeAl (CFA) Heusler alloy. Various possible hypothetical structures: L21-I, L21-II, XA-I, and XA-II were prepared under the conventional L21 and inverse XA phases by altering the atomic occupancies at their Wyckoff sites. It is found that the XA-II phase of CFA is the most stable phase energetically among all the structures. The electronic structure calculations without U show the presence of half-metallic (HM) ground state only in L21-1 structure and the other structures are found to be metallic. However, the electronic structures of CFA are significantly modified in the presence of U, although the total magnetic moments per cell remained the same and consistent with the Slater-Pauling (SP) rule. The metallic ground states of CFA in L21-II and XA-II structures are converted into the half-metallic ground states in presence of U but remained the same (metallic) in XA-I structure. The results indicate that the electronic structures are not only dependent on the L21 and XA ordering of the atoms but also depend on the choice of U values. So experiments may only verify the superiority of GGA+U to GGA.",1906.06516v2 2021-03-06,Observation of inverse magnetocaloric effect in magnetic-field-induced austenite phase of Heusler Alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7),"Magnetocaloric effect (MCE), magnetization, specific heat, and magnetostriction measurements were performed in both pulsed and steady high magnetic fields to investigate the magnetocaloric properties of Heusler alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7). From direct MCE measurements for Ni41Co9Mn31.5Ga18.5 up to 56 T, a steep temperature drop was observed for magnetic-field-induced martensitic transformation (MFIMT), designated as inverse MCE. Remarkably, this inverse MCE is apparent not only with MFIMT, but also in the magnetic-field-induced austenite phase. Specific heat measurements under steady high magnetic fields revealed that the magnetic field variation of the electronic entropy plays a dominant role in the unconventional magnetocaloric properties of these materials. First-principles based calculations performed for Ni41Co9Mn31.5Ga18.5 and Ni45Co5Mn36.7In13.3 revealed that the magnetic-field-induced austenite phase of Ni41Co9Mn31.5Ga18.5 is more unstable than that of Ni45Co5Mn36.7In13.3 and that it is sensitive to slight tetragonal distortion. We conclude that the inverse MCE in the magnetic-field-induced austenite phase is realized by marked change in the electronic entropy through tetragonal distortion induced by the externally applied magnetic field.",2103.04143v1 2021-03-18,Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co$_2$MnGa,"Weyl semimetals are playing a major role in condensed matter physics due to exotic topological properties, and their coexistence with ferromagnetism may lead to enhanced spin-related phenomena. Here, the inverse spin Hall effect (ISHE) in the ferromagnetic Weyl-semimetal Heusler alloy Co$_2$MnGa was investigated at room temperature by means of electrical spin injection in lateral spin valve structures. Spin transport properties such as spin polarization and spin diffusion length in this material were precisely extracted in order to estimate the spin Hall angle $\theta_{\textrm{SH}}$, which was found to be $-0.19\pm0.04$ and is among the highest reported for a ferromagnet. Although this value is on the same order of magnitude of known heavy metals, the significantly higher resistivity of Co$_2$MnGa implies an improvement on the magnitude of detection voltages, while its ferromagnetic nature allows controlling the intensity of SHE through the magnetization direction. It was also shown that Onsager's reciprocity does not hold for this system, which is in part attributable to a different spin-dependent Hall conductivity for spin-up and spin-down carriers.",2103.10188v1 2022-03-20,Deposition temperature dependence of thermo-spin and magneto-thermoelectric conversion in Co$_2$MnGa films on Y$_3$Fe$_5$O$_{12}$ and Gd$_3$Ga$_5$O$_{12}$,"We have characterized Co$_2$MnGa (CMG) Heusler alloy films grown on Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates at different deposition temperatures and investigated thermo-spin and magneto-thermoelectric conversion properties by means of a lock-in thermography technique. X-ray diffraction, magnetization, and electrical transport measurements show that the deposition at high substrate temperatures induces the crystallized structures of CMG while the resistivity of the CMG films on YIG (GGG) prepared at and above 500 {\deg}C (550 {\deg}C) becomes too high to measure the thermo-spin and magneto-thermoelectric effects due to large roughness, highlighting the difficulty of fabricating highly ordered continuous CMG films on garnet structures. Our lock-in thermography measurements show that the deposition at high substrate temperatures results in an increase in the current-induced temperature change for CMG/GGG and a decrease in that for CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen effect in CMG through crystallization. The latter can be explained by the superposition of the anomalous Ettingshausen effect and the spin Peltier effect induced by the positive (negative) charge-to-spin conversion for the amorphous (crystallized) CMG films. These results provide a hint to construct spin-caloritronic devices based on Heusler alloys.",2203.10566v2 2016-03-01,Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys,"Weyl fermions have recently been observed in several time-reversal-invariant semimetals and photonics materials with broken inversion symmetry. These systems are expected to have exotic transport properties such as the chiral anomaly. However, most discovered Weyl materials possess a substantial number of Weyl nodes close to the Fermi level that give rise to complicated transport properties. Here we predict, for the first time, a new family of Weyl systems defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions in the centrosymmetric magnetic systems, we recall an easy and practical inversion invariant, which has been calculated to be -1, guaranteeing the existence of an odd number of pairs of Weyl fermions. These materials exhibit, when alloyed, only two Weyl nodes at the Fermi level - the minimum number possible in a condensed matter system. The Weyl nodes are protected by the rotational symmetry along the magnetic axis and separated by a large distance (of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been calculated as well. This discovery provides a realistic and promising platform for manipulating and studying the magnetic Weyl physics in experiments.",1603.00479v2 2018-04-17,Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy,"Resonant ultrasound spectroscopy and magnetic susceptibility experiments have been used to characterize strain coupling phenomena associated with structural and magnetic properties of the shape-memory Heusler alloy series Ni$_{50+x}$Mn$_{25-x}$Ga$_{25}$ ($x=0$, 2.5, 5.0, and 7.5). All samples exhibit a martensitic transformation at temperature $T_M$ and ferromagnetic ordering at temperature $T_C$, while the pure end member ($x=0$) also has a premartensitic transition at $T_{PM}$, giving four different scenarios: $T_C>T_{PM}>T_M$, $T_C>T_M$ without premartensitic transition, $T_C\approx T_M$, and $T_C 1) is limited to a few chalcogenide TIs with toxic elements and low melting points, making them challenging for device integration during the silicon Back-End-of-Line (BEOL) process. Here, we show that by using a half-Heusler alloy topological semi-metal (HHA-TSM), YPtBi, it is possible to achieve both a giant ${\theta}_{SH}$ up to 1.6 and a high thermal budget up to 600${\deg}$C. We demonstrate magnetization switching of a CoPt thin film using the giant spin Hall effect of YPtBi by current densities lower than those of heavy metals by one order of magnitude. Since HHA-TSM includes a group of three-element topological materials with great flexibility, our work opens the door to the third-generation spin Hall materials with both high ${\theta}_{SH}$ and high compatibility with the BEOL process that would be easily adopted by the industry.",2111.12889v1 2023-01-24,"Ab initio Prediction of Mechanical, Electronic, Magnetic and Transport Properties of Bulk and Heterostructure of a Novel Fe-Cr based Full Heusler Chalcogenide","Using electronic structure calculations based on density functional theory, we predict and study the structural, mechanical, electronic, magnetic and transport properties of a new full Heusler chalcogenide, namely, Fe$_2$CrTe, both in bulk and heterostructure form. The system shows a ferromagnetic and half-metallic(HM) like behavior, with a very high (about 95%) spin polarization at the Fermi level, in its cubic phase. Interestingly, under tetragonal distortion, a clear minimum (with almost the same energy as the cubic phase) has also been found, at a c/a value of 1.26, which, however, shows a ferrimagnetic and fully metallic nature. The compound has been found to be dynamically stable in both the phases against the lattice vibration. The elastic properties indicate that the compound is mechanically stable in both the phases, following the stability criteria of the cubic and tetragonal phases. The elastic parameters unveil the mechanically anisotropic and ductile nature of the alloy system. Due to the HM-like behavior of the cubic phase and keeping in mind the practical aspects, we probe the effect of strain as well as substrate on various physical properties of this alloy. Transmission profile of the Fe$_2$CrTe/MgO/Fe$_2$CrTe heterojunction has been calculated to probe it as a magnetic tunneling junction (MTJ) material in both the cubic and tetragonal phases. Considerably large tunneling magnetoresistance ratio (TMR) of 1000% is observed for the tetragonal phase, which is found to be one order of magnitude larger than that of the cubic phase.",2301.09843v1 2023-03-15,Rare observation of spin-gapless semiconducting characteristics and related band topology of quaternary Heusler alloy CoFeMnSn,"In this paper, we report the theoretical investigation and experimental realization of a new spin-gapless semiconductor (SGSs) compound CoFeMnSn belonging to the family of quaternary Heusler alloys. Through the use of several ground-state energy calculations, the most stable structure has been identified. Calculations of the spin-polarized band structure in optimized structure's reveals the SGS nature of the compound. The compound form in an ordered crystal structure and exhibit a high ferromagnetic transition temperature (T$_{\rm C}$ = 560 K), making the material excellent for room temperature applications. Adherence of saturation magnetization to the Slater-Pauling rule, together with the nearly temperature-independent resistivity, conductivity, and carrier concentration of the compound in the temperature regime 5$-$300 K along with the low value of anomalous Hall conductivity (AHC) further confirms the SGS nature. Theoretical calculations also reveal the robustness of the SGS state due to lattice contraction and one can obtain a high value of intrinsic AHC using hole doping. Combined SGS and topological properties of the compound make CoFeMnSn suitable for spintronics and magneto-electronics devices.",2303.08589v2 2023-07-11,Microstructure of a spark-plasma-sintered Fe2VAl-type Heusler alloy for thermoelectric application,"The influence of microstructure on thermoelectricity is increasingly recognized. Approaches for microstructural engineering can hence be exploited to enhance thermoelectric performance, particularly through manipulating crystalline defects, their structure, and composition. Here, we focus on a full-Heusler Fe2VAl-based compound that is one of the most promising thermoelectric materials containing only Earth-abundant, non-toxic elements. A Fe2VTa0.05Al0.95 cast alloy was atomized under a nitrogen-rich atmosphere to induce nitride precipitation. Nanometer- to micrometer-scale microstructural investigations by advanced scanning electron microscopy and atom probe tomography (APT) are performed on the powder first and then on the material consolidated by spark-plasma sintering for an increasing time. APT reveals an unexpected pick-up of additional impurities from atomization, namely W and Mo. The microstructure is then correlated with local and global measurements of the thermoelectric properties. At grain boundaries, segregation and precipitation locally reduce the electrical resistivity, as evidenced by in-situ four-point probe measurements. The final microstructure contains a hierarchy of structural defects, including individual point defects, dislocations, grain boundaries, and precipitates, that allow for a strong decrease in thermal conductivity. In combination, these effects provide an appreciable increase in thermoelectric performance.",2307.05051v1 2023-09-18,Coherent Tunneling and Strain Sensitivity of an All Heusler Alloy Magnetic Tunneling Junction: A First-Principles Study,"Half-metallic Co-based full Heusler alloys have captured considerable attention of the researchers in the realm of spintronic applications, owing to their remarkable characteristics such as exceptionally high spin polarization at Fermi level, ultra-low Gilbert damping, and high Curie temperature. In this comprehensive study, employing density functional theory, we delve into the stability and electron transport properties of a magnetic tunneling junction (MTJ) comprising a Co$_2$MnSb/HfIrSb interface. Utilizing a standard model given by Julliere, we estimate the tunnel magnetoresistance (TMR) ratio of this heterojunction under external electric field, revealing a significantly high TMR ratio (500%) that remains almost unaltered for electric field magnitudes up to 0.5 V/A. In-depth investigation of K-dependent majority spin transmissions uncovers the occurrence of coherent tunneling for the Mn-Mn/Ir interface, particularly when a spacer layer beyond a certain thickness is employed. Additionally, we explore the impact of bi-axial strain on the MTJ by varying the in-plane lattice constants between -4% and +4%. Our spin-dependent transmission calculations demonstrate that the Mn-Mn/Ir interface manifests strain-sensitive transmission properties under both compressive and tensile strain, and yields a remarkable three-fold increase in majority spin transmission under tensile strain conditions. These compelling outcomes place the Co2MnSb/HfIrSb junction among the highly promising candidates for nanoscale spintronic devices, emphasizing the potential significance of the system in the advancement of the field.",2309.09755v1 2023-09-29,Micromagnetics of ferromagnetic/antiferromagnetic nanocomposite materials. Part II: Mesoscopic modeling,"In the second part of this publication, we present simulation results for two three-dimensional models of Heusler-type alloys obtained by the mesoscopic micromagnetic approach. In the first model, we simulate the magnetization reversal of a single ferromagnetic (FM) inclusion within a monocrystalline antiferromagnetic (AFM) matrix, revealing the evolution of the complex magnetization distribution within this inclusion when the external field is changed. The main result of this ``monocrystalline'' model is the absence of any hysteretic behavior by the magnetization reversal of the FM inclusion. Hence, this model is unable to reproduce the basic experimental result for the corresponding nanocomposite -- hysteresis in the magnetization reversal of FM inclusions with a vertical shift of the corresponding loops. To explain this latter feature, in the second model we introduce a polycrystalline AFM matrix, with exchange interactions between AFM crystallites and between the FM inclusion and these crystallites. We show that within this model we can not only reproduce the hysteretic character of the remagnetization process, but also achieve a semi-quantitative agreement with the experimentally observed hysteresis loop assuming that the concentration of FM inclusions strongly fluctuates. These findings demonstrate the reliability of our enhanced micromagnetic model and set the basis for its applications in future studies of Heusler alloys and FM/AFM nanocomposites.",2309.17129v1 2023-10-03,Complex magnetic interactions and critical behavior analysis in quaternary CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy,"We investigate the magnetic behavior and critical exponents of quaternary CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy to understand the interactions across the Curie temperature ($T_{\rm C}$). The Rietveld refinement of the x-ray diffraction pattern with the space group F$\bar{4}$3m confirms a single-phase cubic Y-type crystal structure. The magnetic susceptibility $\chi (T)$ data show a ferromagnetic nature with a second-order phase transition from paramagnetic to ferromagnetic at $446\pm1$~K. The saturation magnetization at 5~K is determined to be 2.2~$\mu_B$/f.u., which found to be close to the Slater--Pauling rule and indicates its half-metallic nature. The values of asymptotic critical exponents ($\beta$, $\gamma$, and $\delta$) and the $T_{\rm C}$ are extracted through detailed analytical analysis including the Modified Arrott plot, the Kouvel-Fisher (K--F) method, and the Widom scaling relation. Interestingly, the estimated values of $\beta$ = 0.369 and $\gamma$ = 1.445 closely approximate the theoretical values of the 3D Heisenberg model and second-order thermodynamic phase transition across the $T_{\rm C}$. The obtained exponents lead to the collapse of renormalized isotherms, represented by the relationship between the magnetization (m) and the applied magnetic field (h), into two distinct branches above and below the $T_{\rm C}$, which validates the reliability of the analysis. Furthermore, these exponents suggest that the spin interaction follows a decay pattern of $J(r) \sim r^{-4.99}$, indicating a short-range magnetic ordering, akin to the itinerant-electron 3D Heisenberg model.",2310.01790v1 2016-11-06,Lattice thermal conductivity of Ti$_x$Zr$_y$Hf$_{1-x-y}$NiSn half-Heusler alloys calculated from first principles: Key role of nature of phonon modes,"In spite of their relatively high lattice thermal conductivity $\kappa_{\ell}$, the XNiSn (X=Ti, Zr or Hf) half-Heusler compounds are good thermoelectric materials. Previous studies have shown that $\kappa_{\ell}$ can be reduced by sublattice-alloying on the X-site. To cast light on how the alloy composition affects $\kappa_\ell$, we study this system using the phonon Boltzmann-transport equation within the relaxation time approximation in conjunction with density functional theory.The effect of alloying through mass-disorder scattering is explored using the virtual crystal approximation to screen the entire ternary Ti$_x$Zr$_{y}$Hf$_{1-x-y}$NiSn phase diagram. The lowest lattice thermal conductivity is found for the Ti$_x$Hf$_{1-x}$NiSn compositions; in particular, there is a shallow minimum centered at Ti$_{0.5}$Hf$_{0.5}$NiSn with $\kappa_l$ taking values between 3.2 and 4.1 W/mK when the Ti content varies between 20 and 80\%. Interestingly, the overall behavior of mass-disorder scattering in this system can only be understood from a combination of the nature of the phonon modes and the magnitude of the mass variance. Mass-disorder scattering is not effective at scattering acoustic phonons of low energy. By using a simple model of grain boundary scattering, we find that nanostructuring these compounds can scatter such phonons effectively and thus further reduce the lattice thermal conductivity; for instance, Ti$_{0.5}$Hf$_{0.5}$NiSn with a grain size of $L= 100$ nm experiences a 42\% reduction of $\kappa_{\ell}$ compared to that of the single crystal.",1611.01757v2 2016-03-03,"Predicted superconductivity of Ni2VAl and pressure dependence of superconductivity in Ni2NbX (X = Al, Ga and Sn) and Ni2VAl","A first-principles study of the electronic and superconducting properties of the Ni$_2$VAl Heusler compound is presented. The electron-phonon coupling constant of $\lambda_{ep}$ = 0.68 is obtained, which leads to a superconducting transition temperature of T$_c$ = $\sim$4 $K$ (assuming a Coulomb pseudopotential $\mu^*$ = 0.13), which is a relatively high transition temperature for Ni based Heusler alloys. The electronic density of states reveals a significant hybridization between Ni-$eg$ and V-$t_{2g}$ states around the Fermi level. The Fermi surface, consisting of two electron pockets around the X-points of the Brillouin zone, exhibits nesting and leads to a Kohn anomaly of the phonon dispersion relation for the transverse acoustic mode TA2 along the (1,1,0) direction, which is furthermore found to soften with pressure. As a consequence, T$_c$ and $\lambda_{ep}$ vary non-monotonically under pressure. The calculations are compared to similar calculations performed for the Ni$_2$NbX (X = Al, Ga and Sn) Heusler alloys, which experimentally have been identified as superconductors. The experimental trend in T$_c$ is well reproduced, and reasonable quantitative agreement is obtained. The calculated T$_c$ of Ni$_2$VAl is larger than either calculated and observed T$_c$s of any of the Nb compounds. The Fermi surfaces of Ni$_2$NbAl and Ni$_2$NbGa consist of only a single electron pocket around the X point, however under compression second electron pocket similar to that of Ni2VAl emerges only in Ni2NbAl and the Tc increases non monotonically in all the compounds. Fermi surface nesting and associated Kohn anomalies are a common feature of all four compounds, albeit weakest in Ni$_2$VAl.",1603.01104v1 2021-08-26,Magnetoelastic anisotropy in Heusler-type Mn$_{2-δ}$CoGa$_{1+δ}$ films,"Perpendicular magnetization is essential for high-density memory application using magnetic materials. High-spin polarization of conduction electrons is also required for realizing large electric signals from spin-dependent transport phenomena. Heusler alloy is a well-known material class showing the half-metallic electronic structure. However, its cubic lattice nature favors in-plane magnetization and thus minimizes the perpendicular magnetic anisotropy (PMA), in general. This study focuses on an inverse-type Heusler alloy, Mn$_{2-\delta}$CoGa$_{1+\delta}$ (MCG) with a small off-stoichiometry ($\delta$) , which is expected to be a half-metallic material. We observed relatively large uniaxial magnetocrystalline anisotropy constant ($K_\mathrm{u}$) of the order of 10$^5$ J/m$^3$ at room temperature in MCG films with a small tetragonal distortion of a few percent. A positive correlation was confirmed between the $c/a$ ratio of lattice constants and $K_\mathrm{u}$. Imaging of magnetic domains using Kerr microscopy clearly demonstrated a change in the domain patterns along with $K_\mathrm{u}$. X-ray magnetic circular dichroism (XMCD) was employed using synchrotron radiation soft x-ray beam to get insight into the origin for PMA. Negligible angular variation of orbital magnetic moment ($\Delta m_\mathrm{orb}$) evaluated using the XMCD spectra suggested a minor role of the so-called Bruno's term to $K_\mathrm{u}$. Our first principles calculation reasonably explained the small $\Delta m_\mathrm{orb}$ and the positive correlation between the $c/a$ ratio and $K_\mathrm{u}$. The origin of the magnetocrystalline anisotropy was discussed based on the second-order perturbation theory in terms of the spin--orbit coupling, claiming that the mixing of the occupied $\uparrow$- and the unoccupied $\downarrow$-spin states is responsible for the PMA of the MCG films.",2108.11547v2 2018-11-10,Magnetic Order and Lattice Instabilities in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ Heusler based Magnetic Shape-Memory Alloys,"The magnetic correlations in the austenite phase and the consequent martensitic transition in inverse magnetocaloric alloys, Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$, have been a matter of debate for decades. We conclusively establish using {\it ab initio} phonon calculations that the spin alignment of excess Mn at the Sn site (Mn$_{Sn}$) with the existing Mn in the unit cell in the high temperature cubic phase of Ni-Mn-Sn alloy is ferromagnetic (FM), and not ferrimagnetic (FI), resolving a long lasting controversy. Using first principles density functional perturbation theory (DFPT), we observe an instability of the TA$_{2}$ mode along the $\Gamma$-M direction in the FM phase, very similar to that observed in the prototypical ferromagnetic shape memory alloy (FSMA) Ni$_{2}$MnGa. This specific instability is not observed in the FI phase. Further finite temperature first principles lattice dynamics calculations reveal that at 300 K the FM phase becomes mechanically stable, while the FI phase continue to remain unstable providing credence to the fact that the high-temperature phase has FM order. These results will be primordial to understand the magneto-structural properties of this class of compounds.",1811.04221v1 2020-06-09,Effect of partial substitution of iso-valent Mo at Cr-site on electronic structure and physical properties of Fe2CrAl,"Heusler alloy Fe2CrAl exhibits a ferromagnetic behaviour below Curie temperature (TC) ~ 202 K along with presence of cluster glass (CG) phase near freezing temperature (Tf) ~ 3.9 K and Griffiths phase (GP) above 300 K. The physical properties of this alloy are very sensitive to substitutions and anti-site disorder. Here, we investigate the effect of partial substitution of Mo at Cr-site on physical properties of Fe2CrAl. Structural and morphological analysis confirms the single cubic structure of the substituted alloys. Increment in Mo concentration shifts the TC towards lower temperature, which is ascribed to the effect of increased hybridization strength between 3d-4d states of Fe/Cr/Mo. Additionally, systematic analysis of AC susceptibility, magnetic memory effect and time dependent magnetization studies confirm the presence of CG-like phase near (Tf) ~ 3.5 K in Fe2Cr0.95Mo0.05Al. Such feature gets suppressed towards lower temperature with an increase of Mo concentration, i.e. below 1.8 K in Fe2Cr0.85Mo0.15Al. The origin of the glassy signature is ascribed to the decrement in magnetic anisotropy with Mo concentration. A partial increment in magnetic entropy change is also noted near TC with the increase in Mo substitution. Interestingly, at high temperatures (above 350 K), GP phase persists in both the alloys due to the presence of anti-site disorder.",2006.05111v2 2002-07-10,Martensitic transition and magnetoresistance in a Cu-Al-Mn shape memory alloy. Influence of aging,"We have studied the effect of ageing within the miscibility gap on the electric, magnetic and thermodynamic properties of a non-stoichiometric Heusler Cu-Al-Mn shape-memory alloy, which undergoes a martensitic transition from a $bcc$-based ($\beta$-phase) towards a close-packed structure ($M$-phase). Negative magnetoresistance which shows an almost linear dependence on the square of magnetization with different slopes in the $M$- and $\beta$-phases, was observed. This magnetoresistive effect has been associated with the existence of Mn-rich clusters with the Cu$_2$AlMn-structure. The effect of an applied magnetic field on the martensitic transition has also been studied. The entropy change between the $\beta$- and $M$-phases shows negligible dependence on the magnetic field but it decreases significantly with annealing time within the miscibility gap. Such a decrease is due to the increasing amount of Cu$_2$MnAl-rich domains that do not transform martensitically.",0207254v1 2007-07-06,"Effect of surfaces and interfaces on the electronic, magnetic and gap-related properties of the half-metal Co$_2$MnSn","We present state-of-the-art electronic structure calculations for the Co$_2$MnSn full-Heusler alloy. We show that in its bulk form it is a half-metallic ferromagnet with the Fermi level being located within a tiny gap of the minority-spin density of states. Moreover the alloy shows the Slater-Pauling behavior with a total spin magnetic moment in the unit cell of 5 $\mu_B$. In the case of the (001) surfaces, the broken bonds at the surface form a minority band pinned exactly at the Fermi level destroying the half-metallicity. Our calculations reveal that both the interfaces with the non-magnetic metal V and the semiconductor InAs are no more half-metallic due to the different environment of the atoms of the half-metal at the interface. These interface states although localized only at the first few interface layers can become conducting when coupled to defect states and kill the spin-polarization of the current injected from the half-metal into the semiconductor or the non-magnetic metallic spacer.",0707.0941v1 2011-10-25,Surface spin polarization of the non-stoichiometric Heusler compound Co2Mn(alpha)Si,"Using a combined approach of spin-resolved photoemission spectroscopy, band structure and photoemission calculations we investigate the influence of bulk defects and surface states on the spin polarization of Co2Mn(alpha)Si thin films with bulk L21 order. We find that for Mn-poor alloys the spin polarization at EF is negative due to the presence of Co_Mn antisite and minority surface state contributions. In Mn-rich alloys, the suppression of Co(Mn) antisites leads to a positive spin polarization at the Fermi energy, and the influence of minority surface states on the photoelectron spin polarization is reduced.",1110.5451v2 2014-07-11,A 4-fold-symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy and tunnel magnetoresistance,"An unusual crystallographic orientation of hexagonal Ru with a 4-fold symmetry emerging in epitaxial MgO/Ru/Co2FeAl/MgO heterostructures is reported, in which an approximately Ru(02-23) growth attributes to the lattice matching among MgO, Ru, and Co2FeAl. Perpendicular magnetic anisotropy of the Co2FeAl/MgO interface is substantially enhanced as compared with those with a Cr(001) layer. The MTJs incorporating this structure gave rise to the largest tunnel magnetoresistance for perpendicular MTJs using low damping Heusler alloys. The 4-fold-symmetry hexagonal Ru arises from an epitaxial growth with an unprecedentedly high crystal index, opening a unique pathway for the development of perpendicular anisotropy films of cubic and tetragonal ferromagnetic alloys.",1407.3160v2 2015-06-28,Calorimetric and magnetic study for Ni$_{50}$Mn$_{36}$In$_{14}$ and relative cooling power in paramagnetic inverse magnetocaloric systems,"The non-stoichiometric Heusler alloy Ni$_{50}$Mn$_{36}$In$_{14}$ undergoes a martensitic phase transformation in the vicinity of 345 K, with the high temperature austenite phase exhibiting paramagnetic rather than ferromagnetic behavior, as shown in similar alloys with lower-temperature transformations. Suitably prepared samples are shown to exhibit a sharp transformation, a relatively small thermal hysteresis, and a large field-induced entropy change. We analyzed the magnetocaloric behavior both through magnetization and direct field-dependent calorimetry measurements. For measurements passing through the first-order transformation, an improved method for heat-pulse relaxation calorimetry was designed. The results provide a firm basis for the analytic evaluation of field-induced entropy changes in related materials. An analysis of the relative cooling power (RCP), based on the integrated field-induced entropy change and magnetizing behavior of the Mn spin system with ferromagnetic correlations, shows that a significant RCP may be obtained in these materials by tuning the magnetic and structural transformation temperatures through minor compositional changes or local order changes.",1506.08351v1 2016-10-17,Designing compensated magnetic states in tetragonal Mn3Ge-based alloys,"Magnetic compensated state attracted much interests due to the observed large exchange bias and large coercivity, and its potential applications in the antiferromagnetic spintronics with merit of no stray field. In this work, by ab initio calculations with KKR-CPA for the treatment of random substitution, we obtain the complete compensated states in the Ni (Pd, Pt) doped Mn3Ge-based D022-type tetragonal Heusler alloys. We find the total moment change is asymmetric across the compensation point (at ~ x = 0.3) in Mn3-xYxGe (Y = Ni, Pd, Pt), which is highly conforming to that experimentally observed in Mn3Ga. In addition, an uncommon discontinuous jump is observed across the critical zero-moment point, indicating that some non-trivial properties can emerge at this point. Further electronic analysis for the three compensation compositions reveals large spin polarizations, together with the high Curie temperature of the host Mn3Ge, making them promising candidates for spin transfer torque applications.",1610.04971v1 2019-04-04,First-principles investigations of orthorhombic-cubic phase transition and its effect on thermoelectric properties in cobalt-based ternary alloys,"We screened six cobalt-based 18-VEC systems CoVSi, CoNbSi, CoTaSi (Si-group) and CoVGe, CoNbGe, CoTaGe (Ge-group) by the first-principles approach, with the motivation of stabilizing these orthorhombic phases into the cubic symmetry -- favorable for thermoelectrics. Remarkably, it was found that the Ge-group is energetically more favorable in the cubic symmetry than the hitherto orthorhombic phase. We account the cubic ground state of the Si-group to the interplay of internal pressure and covalent interactions. The principle of covalent interactions will provide an insight and could be vital in speeding the search of missing cubic half-Heusler alloys. Meanwhile, the calculated transport properties of all the systems on \textit{p}-type doping, except CoVSi, are more promising than the well-known CoTiSb. We also provide conservative estimates of the figure of merit, exceeding the CoTiSb. Based on our findings, we suggest possible new phases of ternary compounds for thermoelectric applications.",1904.02485v1 2020-04-01,Importance of site occupancy and absence of strain glassy phase in Ni$_{2-x}$Fe$_{x}$Mn$_{1.5}$In$_{0.5}$,"Martensitic transition temperature steadily decreases in Ni$_{2-x}$Fe$_{x}$Mn$_{1.5}$In$_{0.5}$ and is completely suppressed at $x$ = 0.2. Despite suppression of martensitic transition, Ni$_{1.8}$Fe$_{0.2}$Mn$_{1.5}$In$_{0.5}$ does not display the expected strain glassy phase. Instead, a ground state with dominant ferromagnetic interactions is observed. A study of structural and magnetic properties of $x$ = 0.2 reveal that the alloy consists of a major Fe rich cubic phase and a minor Fe deficient monoclinic phase favoring a ferromagnetic ground state. This is exactly opposite of that observed in Ni$_2$Mn$_{1-y}$Fe$_{y}$In$_{0.5}$ wherein a strain glassy phase is observed for $y$ = 0.1. The change in site symmetry of Fe when doped for Ni in contrast to Mn in the Heusler composition seems to support the growth of the ferromagnetic phase.",2004.00256v1 2019-09-28,Size-Dependent Structural and Magnetic Properties of Disordered Co2FeAl Heusler Alloy Nanoparticles,"Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by chemical route. The effect of the size of NPs upon the structure and magnetization compared to its bulk counterpart was investigated. The structure and composition were determined from X-ray diffraction (XRD) and electron microscopy. XRD analysis shows that the samples are having single (A2-type) disordered phase. Magnetization measurements suggest that the samples are soft ferromagnetic in nature with very low coercivity. Enhanced magnetic properties like saturation magnetization, coercive force, retentivity, and Curie-temperature are observed with a decrease in particle size. The effect of particle size on hysteresis losses is also discussed. The smallest particles of size 16 nm exhibited the highest saturation magnetization and transition temperature of 180.73 emu/g and 1261 K, respectively. The origin of enhancement in the magnetization of Co2FeAl nano-alloy is attributed to the strong Co-Co exchange interaction due to disorder present in the systems.",1909.13088v1 2020-03-04,"Theoretical study of phase stability, electronic and magnetic properties of Rh$_2$CrGe$_{1-x}$Al$_x$ ($x = 0$, $0.25$, $0.50$, $0.75$ and $1$) Heusler alloys by FP-LAPW method","First-principle calculations were performed within the framework of the density functional theory (DFT) using FP-LAPW method as implemented in WIEN2k code to determine the structural stability, electronic and magnetic properties of Rh$_2$CrGe$_{1-x}$Al$_x $($x = 0$, $0.25$, $0.50$, $0.75$ and $1$). The results showed that for Rh$_2$CrAl and Rh$_2$CrGe, the Cu$_2$MnAl-type structure is energetically more stable than Hg$_2$CuTi-type structure at the equilibrium volume. The calculated densities of states for Rh$_2$CrAl and Rh$_2$CrGe show half-metallic and nearly half-metallic behavior, respectively. Rh$_2$CrGe$_{1-x}$Al$_x$ ($x = 0.25$, $0.50$, $0.75$) these alloys show a half-metallic character, and these compounds are predicted to be good candidates for spintronic applications.",2003.02067v1 2020-03-25,Crystal and magnetic structure of antiferromagnetic Mn$_{2}$PtPd,"We have investigated the crystal and magnetic structure of Mn${}_{2}$PtPd alloy using powder x-ray and neutron diffraction experiments. This compound is believed to belong to the Heusler family having crystal symmetry $\mathit{I}$4/$\mathit{mmm}$ (TiAl${}_{3}$-type). However, in this work we found that the Pd and Pt atoms are disordered and thus Mn${}_{2}$PtPd crystallizes in the $\mathit{L}$1${}_{0}$ structure having $\mathit{P}$4/$\mathit{mmm}$ symmetry (CuAu-I type) like MnPt and MnPd binary alloys. The lattice constants are $\mathit{a}$ = 2.86 \r{A} and $\mathit{c}$ = 3.62 \r{A} at room temperature. Mn${}_{2}$PtPd has a collinear antiferromagnetic spin structure below the N\'{e}el temperature $\mathit{T}$${}_{N}$ = 866 K, where Mn moments of $\mathrm{\sim}$4 $\mu$${}_{B}$ lie in the $\mathit{ab}$-plane. We observed a strong change in the lattice parameters near $\mathit{T}$${}_{N}$. The sample exhibits metallic behaviour, where electrical resistivity and carrier concentration are of the order of 10${}^{-5}$ $\Omega$ cm and 10${}^{21}$ cm${}^{-3}$, respectively.",2003.11569v1 2020-10-14,"Ab-initio study of electronic and magnetic properties of Mn$_2$RuZ/MgO (001) heterojunctions (Z= Al, Ga, Si, Ge)","Using first-principles calculations, we studied Mn$_2$RuZ (Z=Al, Ga, Si, Ge) and their heterojunctions with MgO along (001) direction. All these alloys possess Hg$_2$CuTi-type inverse Heusler alloy structure and ferrimagnetic ground state. Our study reveals the half-metallic electronic structure with highly spin-polarized $\Delta_1$ band, which is robust against atomic disorder. Next we studied the electronic structure of Mn$_2$RuAl/MgO and Mn$_2$RuGe/MgO heterojunctions. We found that the MnAl- or MnGe-terminated interface is energetically more favorable compared to the MnRu-terminated interface. Interfacial states appear at the Fermi level in the minority-spin gap for the Mn$_2$RuGe/MgO junction. We discuss the origin of these interfacial states in terms of local environment around each constituent atom. On the other hand, in the Mn$_2$RuAl/MgO junction, high spin polarization of bulk Mn$_2$RuAl is preserved independent of its termination.",2010.06761v1 2018-11-30,Spin Gapless Semiconducting Nature in Co-rich Co1+xFe1-xCrGa: Insight and Advancements,"In this report, we present structural, electronic, magnetic and transport properties of Co-rich spin gapless semiconductor CoFeCrGa using both theoretical and experimental techniques. The key advantage of Co-rich samples $\mathrm{Co_{1+x}Fe_{1-x}CrGa}$ is the high Curie temperature (T$\mathrm{_C}$) and magnetization, without compromising the SGS nature (up to x = 0.4), and hence our choice. The quaternary Heusler alloys $\mathrm{Co_{1+x}Fe_{1-x}CrGa}$ (x = 0.1 to 0.5) are found to crystallize in LiMgPdSn-type structure having space group $F\bar{4}3m$ (\# 216). The measured Curie temperature increases from 690 K (x = 0) to 870 K (x = 0.5). Observed magnetization values follow the Slater-Pauling rule. Measured electrical resistivity, in the temperature range of 5-350 K, suggests that the alloys retain the SGS behavior up to x = 0.4, beyond which it reflects metallic character. Unlike conventional semiconductors, the conductivity value ($\mathrm{\sigma_{xx}}$) at 300 K lies in the range of 2289 S $\mathrm{cm^{-1}}$ to 3294 S $\mathrm{cm^{-1}}$, which is close to that of other reported SGS materials. The anomalous Hall effect is comparatively low. The intrinsic contribution to the anomalous Hall conductivity increase with x, which can be correlated with the enhancement in chemical order. The anomalous Hall coefficient is found to increase from 38 S/cm for x = 0.1 to 43 S/cm for 0.3. Seebeck coefficients turn out to be vanishingly small below 300 K, another signature for being SGS. All the alloys (for different x) are found to be both chemically and thermally stable. Simulated magnetization agrees fairly with the experiment. As such Co-rich CoFeCrGa is a promising candidate for room temperature spintronic applications, with enhanced T$\mathrm{_C}$, magnetic properties and SGS nature.",1811.12684v1 2012-09-22,Structural and electronic properties of superconducting Heusler alloy Ni$_{2}$Nb$_{1+x}$Sn$_{1-x}$: \textit{Ab initio} approach,"Using \textit{ab initio} calculation, we investigate systematically the structural and electronic properties of Ni$_{2}$Nb$_{1+x}$Sn$_{1-x}$ ($x$ = 0, 0.25, 0.50). Here, projector augmented wave approach (PAW) implemented in the Vienna \textit{ab initio} simulation package (VASP) within generalized gradient approximation (GGA) for the exchange-correlation functional has been used. In this article, it is reported that though Ni$_{2}$NbSn and Ni$_{2}$Nb$_{1.25}$Sn$_{0.75}$ have no structural transformation, Ni$_{2}$Nb$_{1.5}$Sn$_{0.5}$ can transform to tetragonal structure from cubic L2$_{1}$ phase. The cubic lattice parameter decreases with Nb doping at Sn sites in off-stoichiometric alloys. The alloys are in paramagnetic phase in all the structures. The hybridization between Ni and Nb 3d states triggers the tetragonal distortion. Due to Nb doping in cubic L2$_{1}$ phase, there is a significant change in total density of states (DOSs) at Fermi energy (E$_{F}$) (N(E$_{F}$)). N(E$_{F}$) increases with increasing Nb doping. But, N(E$_{F}$) decreases during structural transformation of Ni$_{2}$Nb$_{1.5}$Sn$_{0.5}$. The superconducting critical temperature (T$_{C}$) also changes with Nb doping in cubic phase and tetragonal distortion because T$_{C}$ very much depends on N(E$_{F}$).",1209.4964v3 2022-08-03,"Machine Learning-Based Classification, Interpretation, and Prediction of High-Entropy-Alloy Intermetallic Phases","The design of high-entropy alloys (HEA) with desired properties is challenging due to their large compositional space. While various machine learning (ML) models can predict specific HEA solid-solution phases (SS), predicting high-entropy intermetallic phases (IM) is underdeveloped due to limited datasets and inadequate ML features. This paper introduces feature engineering-assisted ML models that achieve detailed phase classification and high accuracy. By combining phase-diagram-based and physics-based features, it is found that the ML models trained on the Random Forest (RF) and Support Vector Machine (SVM) regressors, are able to classify individual SS and common IM (Sigma, Laves, Heusler, and refractory B2 phases) with accuracies ranging from 80 - 94%. The machine-learned features also enable the interpretation of IM formation. Furthermore, the efficacies of the RF, SVM, and neural network (NN) models are critically evaluated. The phase classification accuracies are found to decrease upon utilizing the NN model to train the datasets. The accuracy of the model prediction is validated by synthesizing 86 new alloys. This approach provides a practical and robust framework for guiding HEA phase design, particularly for technologically significant IM phases.",2208.02141v3 2024-02-29,Enhanced metamagnetic shape memory effect in Heusler-type Ni37Co11Mn43Sn9 polycrystalline ferromagnetic shape memory alloy,"Polycrystalline Ni-Co-Mn-Sn based ferromagnetic shape memory alloys (FSMAs) show promise as actuator materials, but their practical application involving magnetic field induced strain (MFIS) is often limited by three factors: the requirement for high magnetic fields (> 5 T), martensitic transition temperature away from room temperature, and limited recovery of pre-strain applied to the martensite phase. Current work investigates the martensitic transition (MT) and shape memory effect under the application of magnetic field for bulk polycrystalline Ni37Co11Mn43Sn9 alloy. The outcome of the study reveals a metamagnetic transition from the martensitic phase to the austenitic phase at a low field of 2.8 T at 300 K which results 0.25% spontaneous MFIS. Interestingly, 1.3% pre-strained specimen registers a 100% recovery with the application of magnetic field of 4.5 T. Furthermore, the pre-strained specimen exhibited a two-way shape memory effect between a strain value of 1.0% to 1.55% during the field loading and unloading sequences. Notably, this study also demonstrates, to the best of our knowledge , for the first time, that the spontaneous strain and pre-strain add together. This finding paves the way for achieving a giant MFIS by pre-straining a Ni-Mn-Sn/In class of FSMAs which shows large spontaneous MFIS.",2402.18992v1 2005-10-08,Design of magnetic materials: Co$_2$Cr$_{1-x}$Fe$_{x}$Al,"Doped Heusler compounds Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe ratio $x$ were investigated experimentally and theoretically. The electronic structure of the ordered, doped Heusler compound Co$_2$Cr$_{1-x}$Fe$_{x}$Al ($x=n/4, n=0,1,2,3,4)$ was calculated using different types of band structure calculations. The ordered compounds turned out to be ferromagnetic with small Al magnetic moment being aligned anti-parallel to the 3d transition metal moments. All compounds show a gap around the Fermi-energy in the minority bands. The pure compounds exhibit an indirect minority gap, whereas the ordered, doped compounds exhibit a direct gap. Magnetic circular dichroism (MCD) in X-ray absorption spectra was measured at the $L_{2,3}$ edges of Co, Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to determine element specific magnetic moments. Calculations and measurements show an increase of the magnetic moments with increasing iron content. The experimentally observed reduction of the magnetic moment of Cr can be explained by Co-Cr site-disorder. The presence of the gap in the minority bands of Co$_2$CrAl can be attributed to the occurrence of pure Co$_2$ and mixed CrAl (001)-planes in the $L2_1$ structure. It is retained in structures with different order of the CrAl planes but vanishes in the $X$-structure with alternating CoCr and CoAl planes.",0510203v1 2012-09-29,"Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric CoxMnyGez (x : z = 2 : 0.38) Heusler thin films","Fully epitaxial magnetic tunnel junctions (MTJs) with off-stoichiometric Co2-based Heusler alloy shows a intense dependency of the tunnel magnetoresistance (TMR) on the Mn composition, demonstrating giant TMR ratios of up to 1995% at 4.2 K for 1. This work reports on the electronic structure of non-stoichiometric CoxMnyGez thin films with a fixed Co/Ge ratio of x : z = 2 : 0.38. The electronic structure was investigated by high energy, hard X-ray photoelectron spectroscopy combined with first-principles calculations. The high-resolution measurements of the valence band of the non-stoichiometric CoxMnyGez films close to the Fermi energy indicate a shift of the spectral weight compared to bulk Co2MnGe. This is in agreement with the changes in the density of states predicted by the calculations. Furthermore it is shown that the co-sputtering of Co2MnGe together with additional Mn is an appropriate technique to adjust the stoichiometry of the CoxMnyGez film composition. The resulting changes of the electronic structure within the valence band will allow to tune the magnetoresistive characteristics of CoxMnyGez based tunnel junctions as verified by the calculations and photoemission experiments.",1210.0146v1 2014-08-07,Weak Antilocalization Effect and Noncentrosymmetric Superconductivity in a Topologically Nontrivial Semimetal LuPdBi,"A large number of half-Heusler compounds have been recently proposed as three-dimensional (3D) topological insulators (TIs) with tunable physical properties.However, no transport measurements associated with the topological surface states have been observed in these half-Heusler candidates due to the dominating contribution from bulk electrical conductance. Here we show that, by reducing the mobility of bulk carriers, a two-dimensional (2D) weak antilocalization (WAL) effect, one of the hallmarks of topological surface states, was experimentally revealed from the tilted magnetic field dependence of magnetoconductance in a topologically nontrivial semimetal LuPdBi. Besides the observation of a 2D WAL effect, a superconducting transition was revealed at Tc~1.7 K in the same bulk LuPdBi. Quantitative analysis within the framework of a generalized BCS theory leads to the conclusion that the noncentrosymmetric superconductivity of LuPdBi is fully gapped with a possibly unconventional pairing character. The co-existence of superconductivity and the transport signature of topological surface states in the same bulk alloy suggests that LuPdBi represents a very promising candidate as a topological superconductor.",1408.1543v1 2014-11-21,A new spin gapless semiconductor: quaternary Heusler CoFeCrGa alloy,"Despite a plethora of materials suggested for spintronic applications, a new class of materials has emerged, namely spin gapless semiconductors (SGS), that offers potentially more advantageous properties than existing ones. These magnetic semiconductors exhibit a finite band gap for one spin channel and a closed gap for the other. Here, supported by the first-principles, electronic-structure calculations, we report the first experimental evidence of SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (L21) structure but exhibiting chemical disorder (DO3 structure). CoFeCrGa is found to transform from SGS to half-metallic phase under pressure, which is attributed to unique electronic-structure features. The saturation magnetization (MS) obtained at 8 K agrees with the Slater-Pauling rule and the Curie temperature (TC) is found to exceed 400 K. Carrier concentration (up to 250 K) and electrical conductivity are observed to be nearly temperature independent, prerequisites for SGS. The anomalous Hall coefficient is estimated to be 185 S/cm at 5 K. Considering the SGS properties and high TC, this material appears to be promising for spintronic applications.",1411.5772v2 2015-03-05,Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy,"The magnitude of the spin polarization at the Fermi level of ferromagnetic materials at room temperature is a key property for spintronics. Investigating the Heusler compound Co$_2$MnSi a value of 93$\%$ for the spin polarization has been observed at room temperature, where the high spin polarization is related to a stable surface resonance in the majority band extending deep into the bulk. In particular, we identified in our spectroscopical analysis that this surface resonance is embedded in the bulk continuum with a strong coupling to the majority bulk states. The resonance behaves very bulk-like, as it extends over the first six atomic layers of the corresponding (001)-surface. Our study includes experimental investigations, where the bulk electronic structure as well as surface-related features have been investigated using spin-resolved photoelectron spectroscopy (SR-UPS) and for a larger probing depth spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The results are interpreted in comparison with first-principles band structure and photoemission calculations which consider all relativistic, surface and high-energy effects properly.",1503.01573v1 2017-07-13,"The role of grain boundary scattering in reducing the thermal conductivity of polycrystalline XNiSn (X = Hf, Zr, Ti) half-Heusler alloys","Thermoelectric application of half-Heusler compounds suffers from their fairly high thermal conductivities. Insight into how effective various scattering mechanisms are in reducing the thermal conductivity of fabricated XNiSn compounds (X = Hf, Zr, Ti, and mixtures thereof) is therefore crucial. Here, we show that such insight can be obtained through a concerted theory-experiment comparison of how the lattice thermal conductivity kLat(T) depends on temperature and crystallite size. Comparing theory and experiment for a range of Hf0.5Zr0.5NiSn and ZrNiSn samples reported in the literature and in the present paper revealed that grain boundary scattering plays the most important role in bringing down kLat, in particular so for unmixed compounds. Our concerted analysis approach was corroborated by a good qualitative agreement between the measured and calculated kLat of polycrystalline samples, where the experimental average crystallite size was used as an input parameter for the calculations. The calculations were based on the Boltzmann transport equation and ab initio density functional theory. Our analysis explains the significant variation of reported kLat of nominally identical XNiSn samples and is expected to provide valuable insights into the dominant scattering mechanisms even for other materials.",1707.04302v2 2017-11-29,Methods to induce perpendicular magnetic anisotropy in full-Heusler Co2FeSi thin layers in a magnetic tunnel junction structure,"In this study, to obtain perpendicular magnetic tunnel junctions (p-MTJs) using half-metallic ferromagnets (HMFs), several methods were developed to induce perpendicular magnetic anisotropy (PMA) in full-Heusler Co2FeSi (CFS) alloy thin layers in an MTJ multilayer composed of a layered CFS/MgO/CFS structure. Oxygen exposure at 2.0 Pa for 10 min after deposition of the bottom CFS layer was effective for obtaining PMA in the CFS layer. One of the reasons for the PMA is the formation of nearly ideal CFS/MgO interfaces due to oxygen exposure before the deposition of the MgO layer. The annealing process was effective for obtaining PMA in the top CFS layer capped with a Pd layer. PMA was clearly observed in the top CFS layer of a Cr(40 nm)/Pd(50 nm)/bottom CFS(0.6 nm)/MgO(2.0 nm)/top CFS(0.6 nm)/Pd(10 nm) multilayer, where the top CFS and Pd thin films were deposited at RT and subsequently annealed at 300{\deg}C. In addition to the continuous layer growth of the films, the crystalline orientation alignment at the top CFS/Pd interface probably attributes to the origin of PMA at the top CFS layer.",1711.10722v3 2017-04-26,Ordering tendencies and electronic properties in quaternary Heusler derivatives,"The phase stabilities and ordering tendencies in the quaternary full-Heusler alloys NiCoMnAl and NiCoMnGa have been investigated by in-situ neutron diffraction, calorimetry and magnetization measurements. NiCoMnGa was found to adopt the L2$_1$ structure, with distinct Mn and Ga sublattices but a common Ni-Co sublattice. A second-order phase transition to the B2 phase with disorder also between Mn and Ga was observed at 1160 K. In contrast, in NiCoMnAl slow cooling or low-temperature annealing treatments are required to induce incipient L2$_1$ ordering, otherwise the system displays only B2 order. Linked to this L2$_1$ ordering, a drastic increase in the magnetic transition temperature was observed in NiCoMnAl, while annealing affected the magnetic behavior of NiCoMnGa only weakly due to the low degree of quenched-in disorder. First principles calculations were employed to study the thermodynamics as well as order-dependent electronic properties of both compounds. It was found that a near half-metallic pseudo-gap emerges in the minority spin channel only for the completely ordered Y structure, which however is energetically unstable compared to the predicted ground state of a tetragonal structure with alternating layers of Ni and Co. The experimental inaccessibility of the totally ordered structures is explained by kinetic limitations due to the low ordering energies.",1704.08100v1 2019-10-07,Accurate high-throughput screening of I-II-V 8-electron Half-Heusler compounds for renewable-energy applications,"Renewable energy resources have emerged as the best alternatives to fossil fuel energy which are rapidly declining with time. Here, eight valence-electron count Half-Heusler(HH) alloys have been studied using reliable first principles calculations in the search of potential candidates for renewable energy applications like thermoelectric (TE), solar harvesting, topological insulator (TI) and transparent conductor (TC) applications. The initial screening parameters used for our study are chemical and thermal stability, band gap, nature of bandgap and band inversion strength. We have performed quasistatic G0W0 calculation starting from HSE groundstate wavefunction to predict the most accurate estimation of bandgap for these class of compounds. A total of 960 compounds were simulated. 121 out of 960 compounds were found to be thermally and chemically stable. 31 compounds with bandgap less than 1.5 eV were studied for thermoelectric application out of which 13 compounds were found to show thermoelectric figure of merit ZT > 0.7 for both p-type and n-type conduction. 30 compounds with band gap 1-1.8 eV were studied for optoelectronic application out of which 13 compounds were found to show Spectroscopic Limited Maximum Efficiency (SLME) more than 20%, comparable to existing state of the art materials. 21 compounds were found to show band inversion at ambient conditions which is a necessary condition for topological insulators. The surface band structure calculations for one of the promising candidate was done to check robustness of the topological behaviour. 29 compounds were found to have bandgap more than 2 eV which are promoted for transparent conductor applications with further band engineering. We strongly believe that our calculations will give useful insights to experimentalists for synthesizing and investigating proposed compounds for different energy applications.",1910.02984v1 2019-10-15,Impact of the scattering physics on the power factor of complex thermoelectric materials,"We assess the impact of the scattering physics assumptions on the thermoelectric properties of five Co-based p-type half-Heusler alloys by considering full energy-dependent scattering times, versus the commonly employed constant scattering time. For this, we employ DFT bandstructures and a full numerical scheme that uses Fermi's Golden Rule to extract the momentum relaxation times of each state at every energy, momentum, and band. We consider electron-phonon scattering (acoustic and optical), as well as ionized impurity scattering, and evaluate the qualitative and quantitative differences in the power factors of the materials compared to the case where the constant scattering time is employed. We show that the thermoelectric power factors extracted from the two different methods differ in terms of i) their ranking between materials, ii) the carrier density where the peak power factor appears, and iii) their trends with temperature. We further show that the constant relaxation time approximation smoothens out the richness in the bandstructure features, thus limiting the possibilities of exploring this richness for material design and optimization. These details are more properly captured under full energy/momentum-dependent scattering time considerations. Finally, by mapping the conductivities extracted within the two schemes, we provide appropriate density-dependent constant relaxation times that could be employed as a fast first order approximation for extracting charge transport properties in the half-Heuslers we consider.",1910.06628v3 2018-12-12,First-principles prediction of half-Heusler half-metals above room temperature,"Half-metallicity (HM) offers great potential for engineering spintronic applications, yet only few magnetic materials present metallicity in just one spin channel. In addition, most HM systems become magnetically disordered at temperatures well below ambient conditions, which further hinders the development of spin-based electronic devices. Here, we use first-principles methods based on density functional theory (DFT) to investigate the electronic, magnetic, structural, mixing, and vibrational properties of $90$ $XYZ$ half-Heusler (HH) alloys ($X =$ Li, Na, K, Rb, Cs; $Y =$ V,Nb, Ta; $Z =$ Si, Ge, Sn, S, Se, Te). We disclose a total of $28$ new HH compounds that are ferromagnetic, vibrationally stable, and HM, with semiconductor band gaps in the range of $1$-$4$ eV and HM band gaps of $0.2$-$0.8$ eV. By performing Monte Carlo simulations of a spin Heisenberg model fitted to DFT energies, we estimate the Curie temperature, $T_{\rm C}$, of each HM compound. We find that $17$ HH HM remain magnetically ordered at and above room temperature, namely, $300 \le T_{\rm C} \le 450$ K, with total magnetic moments of $2$ and $4$ $\mu_{\rm B}$. A further materials sieve based on zero-temperature mixing energies let us to conclude $5$ overall promising ferromagnetic HH HM at and above room temperature: NaVSi, RbVTe, CsVS, CsVSe, and RbNbTe. We also predict $2$ ferromagnetic materials that are semiconductor and magnetically ordered at ambient conditions: LiVSi and LiVGe.",1812.04813v1 2020-08-09,"Ab initio study of the half-metallic full-Heusler compounds Co$_2$ZAl [Z = Sc, Ti, V, Cr, Mn, Fe]; the role of electronic correlations","We study the structural, electronic, and magnetic properties of Co$_2$ZAl compounds employing a pseudopotential electronic bandstructure method. The stability of the compounds is established through the formation and cohesive energy calculations. The effect of the lattice parameter variation on the electronic and magnetic properties of the compounds is investigated and meticulous explanation is provided for the observed behavior. The variation of the individual spin magnetic moments and the stability of the total spin magnetic moment during the expansion and contraction of the lattice parameter is observed and an attempt is made to understand the obtained behavior. Finally, we implement DFT+U to examine its consequences on the electronic and magnetic properties of the Co$_2$ZAl compounds. We find that the use of DFT+U is not justified for these compounds and in some cases like Co$_2$MnAl it produces unrealistic properties. The exception is Co2FeAl where the desired half-metallicity is restored after the inclusion of on-site correlations. We explain why the on-site correlations might be important for Co$_2$FeAl by comparing it with other Heusler alloys where the correlation was found to be meaningful to explain the observed magnetic moments.",2008.03732v1 2020-08-28,Effect of Bi-substitution on Structural Stability and Improved Thermoelectric Performance of p-type Half-Heusler TaSbRu: A First-principles Study,"Recently, Fang et al. have predicted a high ZT of 1.54 in TaSbRu alloys at 1200 K from first-principles without considering spin-orbit interaction, accurate electronic structure, details of phonon scattering, and energy-dependent holes relaxation time. Here, we report the details of structural stability and thermoelectric performance of Bi-Substituted p-type TaSbRu from first-principles calculations considering theses important parameters. This indirect bandgap semiconductor (Eg=0.8 eV by TB-mBJ+SOC) has highly dispersive and degenerate valence bands, which lead to a maximum power factor, 3.8 mWm-1K-2 at 300K. As Sb-5p has a small contribution to the bandgap formation, the substitution of Bi on the Sb site does not cause significant change to the electronic structure. Although the Seebeck coefficient increases by Bi due to slight changes in the bandgap, electrical conductivity, and hence, the power factor reduces to ~3 mW m-1K-2 at 300K (50% Bi). On the other side, lattice thermal conductivity drops effectively to 5 from 20 W/m K as Bi introduces a significant contribution in the acoustic phonon region and intensify phonon scattering. Thus, ZT value is improved through Bi-substitution, reaching 1.1 (50% Bi) at 1200 K from 0.45 (pure TaSbRu) only. Therefore, the present study suggests how to improve the TE performance of Sb-based half-Heusler compounds and TaSbRu (with 50% Bi) is a promising material for high-temperature applications.",2008.12564v1 2019-12-21,Non-collinear antiferromagnetic states in Ru-based Heusler compounds induced by biquadratic coupling,"We investigate the magnetic properties of Ru$_{2}$Mn$Z$ ($Z$ = Sn, Sb, Ge, Si) chemically ordered full Heusler compounds for zero as well as finite temperatures. Based on first principles calculations we derive the interatomic isotropic bilinear and biquadratic couplings between Mn atoms from the paramagnetic state. We find frustrated isotropic couplings for all compounds and in case of $Z$ = Si and Sb a nearest-neighbor biquadratic coupling that favors perpendicular alignment between the Mn spins. By using an extended classical Heisenberg model in combination with spin dynamics simulations we obtain the magnetic equilibrium states. From these simulations we conclude that the biquadratic coupling, in combination with the frustrated isotropic interactions, leads to non-collinear magnetic ground states in the Ru$_{2}$MnSi and Ru$_{2}$MnSb compounds. In particular, for these alloys we find two distinct, non-collinear ground states which are energetically equivalent and can be identified as $3-q$ and $4-q$ states on a frustrated fcc lattice. Investigating the thermal stability of the non-collinear phase we find that in case of Ru$_{2}$MnSi the multiple$-q$ phase undergoes a transition to the single$-q$ phase, while in case of Ru$_{2}$MnSb the corresponding transition is not obtained due to the larger magnitude of the nearest-neighbor biquadratic coupling.",1912.10299v1 2020-10-16,THz range Faraday rotation in the Weyl Semimetal Candidate $\mathrm{Co_2TiGe}$,"The $\mathrm{Co_2}$ family of ferromagnetic Heusler alloys have attracted interest due to their fully spin-polarized nature, making them ideal for applications in spintronic devices. More recently, the existence of room temperature time-reversal-breaking Weyl nodes near the Fermi level was predicted and confirmed in these systems. As a result of the presence of these Weyl nodes, these systems possess a non-zero momentum space Berry curvature that can dramatically influence transport properties such as the anomalous Hall effect. One of these candidate compounds is $\mathrm{Co_2 Ti Ge}$. Recently, high quality molecular beam epitaxy-grown thin films of $\mathrm{Co_2 Ti Ge}$ have become available. In this work, we present THz-range measurement of MBE-grown $\mathrm{Co_2 Ti Ge}$ films. We measure the THz-range Faraday rotation, which can be understood as a measure of the anomalous Hall effect. We supplement this work with electronic band structure calculations showing that the principal contribution to the anomalous Hall effect in the this material stems from the Berry curvature of the material. Our work shows that this class of Heusler materials shows promise for Weyl semimetal based spintronics.",2010.08589v2 2020-12-03,When Band Convergence is Not Beneficial for Thermoelectrics,"Band convergence is considered a clear benefit to thermoelectric performance because it increases the charge carrier concentration for a given Fermi level, which typically enhances charge conductivity while preserving the Seebeck coefficient. However, this advantage hinges on the assumption that interband scattering of carriers is weak or insignificant. With first-principles treatment of electron-phonon scattering in CaMg$_{2}$Sb$_{2}$-CaZn$_{2}$Sb$_{2}$ Zintl system and full Heusler Sr$_{2}$SbAu, we demonstrate that the benefit of band convergence can be intrinsically negated by interband scattering depending on the manner in which bands converge. In the Zintl alloy, band convergence does not improve weighted mobility or the density-of-states effective mass. We trace the underlying reason to the fact that the bands converge at one k-point, which induces strong interband scattering of both the deformation-potential and the polar-optical kinds. The case contrasts with band convergence at distant k-points (as in the full Heusler), which better preserves the single-band scattering behavior thereby successfully leading to improved performance. Therefore, we suggest that band convergence as thermoelectric design principle is best suited to cases in which it occurs at distant k-points.",2012.02272v2 2023-05-25,Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100 fs timescales,"The direct manipulation of spins via light may provide a path toward ultrafast energy-efficient devices. However, distinguishing the microscopic processes that can occur during ultrafast laser excitation in magnetic alloys is challenging. Here, we study the Heusler compound Co2MnGa, a material that exhibits very strong light-induced spin transfers across the entire M-edge. By combining the element-specificity of extreme ultraviolet high harmonic probes with time-dependent density functional theory, we disentangle the competition between three ultrafast light-induced processes that occur in Co2MnGa: same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast spin-flips mediated by spin-orbit coupling. By measuring the dynamic magnetic asymmetry across the entire M-edges of the two magnetic sublattices involved, we uncover the relative dominance of these processes at different probe energy regions and times during the laser pulse. Our combined approach enables a comprehensive microscopic interpretation of laser-induced magnetization dynamics on timescales shorter than 100 fs.",2305.16455v2 2023-09-09,Accelerating Discovery of Vacancy Ordered 18-Valence Electron Half-Heusler Compounds: A Synergistic Approach of Machine Learning and Density Functional Theory,"In this study, we attempted to model vacancy ordered half Heusler compounds with 18 valence electron count (VHH) derived from 19 VEC compounds such as TiNiSb such that the compositions will be Ti0.75NiSb, Zr0.75NiSb and Hf0.75NiSb with semiconducting behavior. The main motivation is that such a vacancy-ordered phase not only introduces semi conductivity but also it disrupts the phonon conducting path in HH alloys and thus reduces the thermal conductivity and as a consequence enhances the thermoelectric figure of merit. In order to predict the formation energy ({\Delta}Hf) from composition and crystal structure we have used 4684 compounds for their {\Delta}Hf values are available in the material project database and trained a machine learning model with R2 value of 0.943. Using this trained model, we have predicted the {\Delta}Hf of a list of VHH. From the predicted database of VHH we have selected Zr0.75NiSb and Hf0.75NiSb to validate the machine learning prediction using accurate DFT calculation. The calculated {\Delta}Hf for these two compounds from DFT calculation are found to be comparable with our ML prediction. The calculated electronic and lattice dynamics properties show that these materials are narrow band gap semiconductors and are dynamically stable as their all-phonon dispersion curves are having positive frequencies. The calculated Seebeck coefficient, electrical conductivity as well as thermal conductivity, power factor and thermoelectric figure of merit are analyzed.",2309.04692v1 2017-11-14,"Growth, electrical, structural, and magnetic properties of half-Heusler CoTi$_{1-x}$Fe$_x$Sb","Epitaxial thin films of the substitutionally alloyed half-Heusler series CoTi$_{1-x}$Fe$_x$Sb were grown by molecular beam epitaxy on InAlAs/InP(001) substrates for concentrations 0.0$\leq$x$\leq$1.0. The influence of Fe on the structural, electronic, and magnetic properties was studied and compared to that expected from density functional theory. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and X-ray diffraction. Using in-situ X-ray photoelectron spectroscopy, only small changes in the valence band are detected for x$\leq$0.5. For films with x$\geq$0.05, ferromagnetism is observed in SQUID magnetometry with a saturation magnetization that scales linearly with Fe content. A dramatic decrease in the magnetic moment per formula unit occurs when the Fe is substitutionally alloyed on the Co site indicating a strong dependence on the magnetic moment with site occupancy. A crossover from both in-plane and out-of-plane magnetic moments to only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic resonance indicates a transition from weak to strong interaction with a reduction in inhomogeneous broadening as Fe content is increased. Temperature-dependent transport reveals a semiconductor to metal transition with thermally activated behavior for x$\leq$0.5. Anomalous Hall effect and large negative magnetoresistance (up to -18.5% at 100 kOe for x=0.3) are observed for higher Fe content films. Evidence of superparamagnetism for x=0.3 and x=0.2 suggests for moderate levels of Fe, demixing of the CoTi$_{1-x}$Fe$_x$Sb films into Fe rich and Fe deficient regions may be present. Atom probe tomography is used to examine the Fe distribution in a x=0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe atoms throughout the film, which is used to explain the observed magnetic and electrical behavior.",1711.05320v1 2019-03-07,"Uniaxial anisotropy, intrinsic and extrinsic damping in Co$_{2}$FeSi Heusler alloy thin films","Ferromagnetic resonance (FMR) technique has been used to study the magnetization relaxation processes and magnetic anisotropy in two different series of the Co2FeSi (CFS) Heusler alloy thin films, deposited on the Si(111) substrate by UHV sputtering. While the CFS films of fixed (50 nm) thickness, deposited at different substrate temperatures (TS) ranging from room temperature (RT) to 600^C, constitute the series-I, the CFS films with thickness t varying from 12 nm to 100 nm and deposited at 550^C make up the series-II. In series-I, the CFS films deposited at TS = RT and 200^C are completely amorphous, the one at TS = 300^C is partially crystalline, and those at TS equal 450^C, 550^C and 600^C are completely crystalline with B2 order. By contrast, all the CFS films in series-II are in the fully-developed B2 crystalline state. Irrespective of the strength of disorder and film thickness, angular variation of the resonance field in the film plane unambiguously establishes the presence of global in-plane uniaxial anisotropy. Angular variation of the linewidth in the film plane reveals that, in the CFS thin films of varying thickness, a crossover from the in-plane local four-fold symmetry (cubic anisotropy) to local two-fold symmetry (uniaxial anisotropy) occurs as t exceeds 50 nm. Gilbert damping parameter {\alpha} decreases monotonously from 0.047 to 0.0078 with decreasing disorder strength (increasing TS) and jumps from 0.008 for the CFS film with t = 50 nm to 0.024 for the film with t equal 75 nm. Such variations of {\alpha} with TS and t are understood in terms of the changes in the total (spin-up and spin-down) density of states at the Fermi level caused by the disorder and film thickness.",1903.02976v1 2019-09-18,Neutron diffraction and magnetic properties of Co$_2$Cr$_{1-x}$Ti$_x$Al Heusler alloys,"We report the structural, magnetic, and magnetocaloric properties of Co$_2$Cr$_{1-x}$Ti$_x$Al ($x=$ 0--0.5) Heusler alloys for spintronic and magnetic refrigerator applications. Room temperature X-ray diffraction and neutron diffraction patterns along with Rietveld refinements confirm that the samples are of single phase and possess a cubic structure. Interestingly, magnetic susceptibly measurements indicate a second order phase transition from paramagnetic to ferromagnetic where the Curie temperature (T$_{\rm C}$) of Co$_2$CrAl increases from 330~K to 445~K with Ti substitution. Neutron powder diffraction data of the $x=$ 0 sample across the magnetic phase transition taken in a large temperature range confirm the structural stability and exclude the possibility of antiferromagnetic ordering. The saturation magnetization of the $x=$ 0 sample is found to be 8000~emu/mol (1.45~$\mu_{\rm B}$/{\it f.u.}) at 5~K, which is in good agreement with the value (1.35$\pm$0.05~$\mu_{\rm B}$/{\it f.u.}) obtained from the Rietveld analysis of the neutron powder diffraction pattern measured at temperature of 4~K. By analysing the temperature dependence of the neutron data of the $x=$ 0 sample, we find that the change in the intensity of the most intense Bragg peak (220) is consistent with the magnetization behavior with temperature. Furthermore, an enhancement of change in the magnetic entropy and relative cooling power values has been observed for the $x=$ 0.25 sample. Interestingly, the critical behavior analysis across the second order magnetic phase transition and extracted exponents ($\beta\approx$ 0.496, $\gamma\approx$ 1.348, and $\delta\approx$ 3.71 for the $x=$ 0.25 sample) suggest the presence of long-range ordering, which deviates towards 3D Heisenberg type interactions above T$_{\rm C}$, consistent with the interaction range value $\sigma$.",1909.08292v1 2021-11-02,Microstructure engineering of metamagnetic Ni-Mn-based Heusler compounds by Fe-doping: A roadmap towards excellent cyclic stability combined with large elastocaloric and magnetocaloric effects,"Ni-Mn-based metamagnetic shape-memory alloys exhibit a giant thermal response to magnetic fields and uniaxial stress which can be utilized in single caloric or multicaloric cooling concepts for energy-efficient and sustainable refrigeration. However, during cyclic operation these alloys suffer from structural and functional fatigue as a result of their high intrinsic brittleness. Here, we present based on Fe-doping of Ni-Mn-In a microstructure design strategy which simultaneously improves cyclic stability and maintains the excellent magnetocaloric and elastocaloric properties. Our results reveal that precipitation of a strongly Fe-enriched and In-depleted coherent secondary gamma-phase at grain boundaries can ensure excellent mechanical stability by hindering intergranular fracture during cyclic loading. In this way, a large elastocaloric effect of -4.5 K was achieved for more than 16000 cycles without structural or functional degradation, which corresponds to an increase of the cyclic stability by more than three orders of magnitude as compared to single-phase Ni-Mn-In-(Fe). In addition, we demonstrate that the large magnetocaloric effect of single-phase Ni-Mn-In-(Fe) can be preserved in the dual-phase material when the secondary gamma-phase is exclusively formed at grain boundaries as the martensitic transformation within the Heusler matrix is barely affected. This way, an adiabatic temperature change of -3 K and an isothermal entropy change of 15 $Jkg^{-1}K^{-1}$ was obtained in 2 T for dual-phase Ni-Mn-In-Fe. We expect that this concept can be applied to other single caloric and mutlicaloric materials, therewith paving the way for solid-state caloric cooling applications.",2111.01621v2 2023-01-10,Dissipation losses limiting first-order phase transition materials in cryogenic caloric cooling: A case study on all-d-metal Ni(-Co)-Mn-Ti Heusler alloys,"Ni-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are highly promising materials for energy-efficient solid-state refrigeration as large multicaloric effects can be achieved across their magnetostructural martensitic transformation. However, no comprehensive study on the crucially important transition entropy change $\Delta s_t$ exists so far for Ni(-Co)-Mn-Ti. Here, we present a systematic study analyzing the composition and temperature dependence of $\Delta s_t$. Our results reveal a substantial structural entropy change contribution of approximately 65 J(kgK)$^{-1}$, which is compensated at lower temperatures by an increasingly negative entropy change associated with the magnetic subsystem. This leads to compensation temperatures $T_{comp}$ of 75 K and 300 K in Ni$_{35}$Co$_{15}$Mn$_{50-y}$Ti$_{y}$ and Ni$_{33}$Co$_{17}$Mn$_{50-y}$Ti$_{y}$, respectively, below which the martensitic transformations are arrested. In addition, we simultaneously measured the responses of the magnetic, structural and electronic subsystems to the temperature- and field-induced martensitic transformation near $T_{comp}$, showing an abnormal increase of hysteresis and consequently dissipation energy at cryogenic temperatures. Simultaneous measurements of magnetization and adiabatic temperature change $\Delta T_{ad}$ in pulsed magnetic fields reveal a change in sign of $\Delta T_{ad}$ and a substantial positive and irreversible $\Delta T_{ad}$ up to 15 K at 15 K as a consequence of increased dissipation losses and decreased heat capacity. Most importantly, this phenomenon is universal, it applies to any first-order material with non-negligible hysteresis and any stimulus, effectively limiting the utilization of their caloric effects for gas liquefaction at cryogenic temperatures.",2301.03934v1 2023-03-15,High spin-polarization in a disordered novel quaternary Heusler alloy FeMnVGa,"In this work, we report the successful synthesis of a Fe-based novel half-metallic quaternary Heusler alloy FeMnVGa and its structural, magnetic and transport properties probed through different experimental methods and theoretical technique. Density functional theory (DFT) calculations performed on different types of structure reveal that Type-2 ordered structure (space group: F-43m, Ga at 4a, V at 4b, Mn at 4c and Fe at 4d) possess minimum energy among all the ordered variants. Ab-initio simulations in Type 2 ordered structure further reveal that the compound is half-metallic ferromagnet (HMF) having a large spin-polarization (89.9 %). Neutron diffraction reveal that the compound crystalizes in disordered Type-2 structure (space group: Fm-3m) in which Ga occupy at 4a, V at 4b and Fe/Mn occupy 4c/4d sites with 50:50 proportions. The structural disorder is further confirmed by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS),57Fe Mossbauer spectrometry results and DFT calculations. Magnetisation studies suggest that the compound orders ferromagnetically below TC ~ 293 K and the saturation magnetization follows Slater-Pauling rule. Mossbauer spectrometry, along with neutron diffraction suggest that Mn is the major contributor to the total magnetism in the compound consistent with the theoretical calculations. First principle calculations indicate that spin-polarization remain high (81.3 %) even in the presence of such large atomic disorder. The robustness of the HMF property in presence of disorder is a quite unique characteristic over other reported HMF in literature and make this compound quiet promising for spintronics applications.",2303.08579v1 2015-09-30,Roadmap for Emerging Materials for Spintronic Device Applications,"The Technical Committee of the IEEE Magnetics Society has selected 7 research topics to develop their roadmaps, where major developments should be listed alongside expected timelines; (i) hard disk drives, (ii) magnetic random access memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and actuators, (vi) magnetic materials and (vii) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used for example as a cell for a magnetic random access memory and spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarised electrons efficiently into a non-magnet. We have accordingly identified 2 key properties to be achieved by developing new magnetic materials for future spintronic devices: (1) Half-metallicity at room temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For the first property, 5 major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: Heusler alloys, ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level EF only for its minority spins, achieving 100% spin polarisation at EF. We have also evaluated L10-alloys and D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet with large spin polarisation. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations and interdisciplinary applications within 35 years time scale.",1509.08997v1 2017-07-16,Competing magnetic and spin gap-less semiconducting behaviour in fully compensated ferrimagnet CrVTiAl: Theory and Experiment,"We report the structural, magnetic and transport properties of polycrystalline CrVTiAl alloy along with first principles calculations. It crystallizes in the LiMgPdSn type structure with lattice parameter 6.14 \AA\ at room temperature. Absence of (111) peak along with the presence of a weak (200) peak indicates the antisite disorder of Al with Cr and V atoms. The magnetization measurements reveal a ferrimagnetic transition near 710 K and a coercive field of 100 Oe at 3 K. Very low moment and coercive field indicate fully compensated ferrimagnetism in the alloy. Temperature coefficient of resistivity is found to be negative, indicating a characteristic of semiconducting nature. Absence of exponential dependence of resistivity on temperature indicates a gapless/spin-gapless semiconducting behaviour. Electronic and magnetic properties of CrVTiAl for three possible crystallograpic configurations are studied theoretically. All the three configurations are found to be different forms of semiconductors. Ground state configuration is a fully compensated ferrimagnet with band gaps 0.58 eV and 0.30 eV for up and down spin bands respectively. The next higher energy configuration is also ferrimagnetic, but has spin-gapless semiconducting nature. The highest energy configuration corresponds to a non-magnetic gapless semiconductor. The energy differences among these configurations are quite small ($<$ 1 $\mathrm{mRy/atom}$) which hints that at finite temperatures, the alloy exists in a disordered phase, which is a mixture of the three configurations. By taking into account the theoretical and the experimental findings, we conclude that CrVTiAl is a fully compensated ferrimagnet with predominantly spin gap-less semiconductor nature.",1707.04854v1 2010-11-01,Modeling materials with optimized transport properties,"Following demands for materials with peculiar transport properties, e.g. in magnetoelectronics or thermoelectrics, there is a need for materials modeling at the quantum-mechanical level. We combine density-functional with various scale-bridging tools to establish correlations between the macroscopic properties and the atomic structure of materials. For examples, magnetic memory devices exploiting the tunneling magneto-resistance (TMR) effect depend crucially on the spin polarization of the electrodes. Heusler alloys, e.g. Co2MnSi, if perfectly ordered, are ferromagnetic half-metals with (ideally) 100% spin polarization. Their performance as electrodes in TMR devices is limited by atomic disorder and deviations from perfect stoichiometry, but also by interface states at the tunneling barrier. We use ab initio thermodynamics in conjunction with the cluster expansion technique to show that excess manganese in the alloy and at the interface helps to preserve the desired half-metallic property. As another example, nanostructured materials with a reduced thermal conductivity but good electrical conductivity are sought for applications in thermoelectrics. Semiconductor heterostructures with a regular arrangement of nanoscale inclusions ('quantum dot superlattices') hold the promise of a high thermoelectric figure of merit. Our theoretical analysis reveals that an increased figure of merit is to be expected if the quantum dot size, the superlattice period and the doping level are all suitably fine-tuned. Such a superlattice thus constitutes a material whose transport properties are controlled by geometrical features at the nanoscale.",1011.0324v1 2012-10-19,"Ferromagnetic structures in Mn2CoGa and Mn2CoAl doped by Co, Cu, V, and Ti","The structure and magnetic properties in doped Heusler alloys of Mn2CoGa and Mn2CoAl have been investigated by experiments and calculations. The main group elements of Ga and Al are substituted by the magnetic or non-magnetic transition metals, Co, Cu, V, and Ti in the alloy systems. Three kinds of local ferromagnetic structures, Co-Mn-Co, Mn-Co-Mn and Mn-Co-V, have been found. They embed in the native ferrimagnetic matrix and increase the magnetization with different increments. The Co-Mn-Co ferromagnetic structure shows the largest increment of 6.18{\mu}B /atom. In addition, interesting results for non-magnetic Cu increasing the magnetization and the V atom having a large ferromagnetic moment of about 1.0{\mu}B have been obtained. The exchange interaction energy can be increased by the newly added Co and depleted by supporting a ferromagnetic coupling in other substitution cases, and showing the variation of the TC. Our calculation of electronic structure verifies the strong d-d hybridization when the three ferromagnetic structures are achieved. It has also been found that the covalent effect from the Ga and Al determines the generation of the local ferromagnetic structure and the tolerance for dopant content.",1210.5357v1 2020-11-01,Bipolar Magnetic Semiconducting Behavior in VNbRuAl: A New Spintronic Material for Spin Filters,"We report the theoretical prediction of a new class of spintronic materials, namely bipolar magnetic semiconductor (BMS), which is also supported by our experimental data. BMS acquires a unique band structure with unequal band gaps for spin up and down channels, and thus are useful for tunable spin transport based applications such as spin filters. The valence band (VB) and conduction band (CB) in BMS approach the Fermi level through opposite spin channels, and hence facilitate to achieve reversible spin polarization which are controllable via applied gate voltage. We report the quaternary Heusler alloy VNbRuAl to exactly possess the band structure of BMS. The alloy is found to crystallize in LiMgPdSn prototype structure (space group $F\bar{4}3m$) with B$2$ disorder and lattice parameter 6.15 \AA . The resistivity and Hall measurements show a two channel semiconducting behavior and a quasi linear dependence of negative magneto resistance (MR) indicating the possible semiconducting nature. Interestingly, VNbRuAl also shows a fully compensated ferrimagnetic (FCF) behavior with vanishing net magnetization (m$_s$$\sim$ $10^{-3}$ $\mu_B/f.u.$) and significantly high ordering temperature ($> 900$ K). Unlike conventional FCF, vanishing moment in this case appears to be the result of a combination of long range antiferromagnetic (AFM) ordering and the inherent B2 disorder of the crystal. This study opens up the possibility of finding a class of materials for AFM spintronics, with great significance both from fundamental and applied fronts.",2011.00533v1 2022-05-16,First principle studies on electronic and thermoelectric properties of Fe$_{2}$TiSn based multinary Heusler alloys,"The alloys with 8/18/24 valence electron count (VEC) are promising candidates for efficient energy conversion and refrigeration applications at low as well as high temperatures. The full potential linearized augmented plane wave method as implemented in WIEN2k code was used to investigate electronic structure and TE transport properties with the PBE$-$GGA and TB$-$mBJ exchange potentials and Boltzmann transport theory. The calculated single crystal elastic constants, phonon dispersion and phonon density of states confirm that these systems are mechanically and dynamically stable. The TE transport properties is calculated by including the lattice part of thermal conductivity ($\kappa_{L}$) obtained from two methods one from the calculated elastic properties calculation ($\kappa^{elastic}_{L}$) and the other from phonon dispersion curve ($\kappa^{phonon}_{L}$). The strong phonon$-$phonon scattering by large mass difference/strain fluctuation of isovalent/aliovalent substitution at Ti/Sn sites of Fe$_{2}$TiSn reduces the lattice thermal conductivity which results in high \textit{ZT} value of 0.81 at 900\,K for Fe$_{2}$Sc$_{0.25}$Ti$_{0.5}$Ta$_{0.25}$Al$_{0.5}$Bi$_{0.5}$. The comparative analysis of TE transport properties using the band structures calculated with the PBE$-$GGA and TB$-$mBJ functional shows that the \textit{ZT} value obtained from TB$-$mBJ scheme is found to be significantly higher than that based on PBE$-$GGA. The calculated relatively low lattice thermal conductivity and high \textit{ZT} values suggest that isovalent/aliovalent substituted Fe$_{2}$TiSn are promising candidates for medium to high temperature waste heat recovery.",2205.07688v1 2022-12-05,Quantifying nonadiabaticity in major families of superconductors,"The classical Bardeen-Cooper-Schrieffer and Eliashberg theories of the electron-phonon-mediated superconductivity are based on the Migdal theorem, which is an assumption that the energy of charge carriers, $k{_B}T{_F}$, significantly exceeds the phononic energy, $\hbar{\omega{_D}} $, of the crystalline lattice. This assumption, which is also known as adiabatic approximation, implies that the superconductor exhibits fast charge carriers and slow phonons. This picture is valid for pure metals and metallic alloys because these superconductors exhibit $\hbar{\omega{_D}}$/$k{_B}T{_F}<0.01$. However, n-type doped semiconducting $SrTiO_3$ was the first superconductor which beyond this adiabatic approximation, because this material exhibits $\hbar{\omega{_D}}$/$k{_B}T{_F} $~$ 50$. There is growing number of newly discovered superconductors which also beyond the adiabatic approximation. Here, leaving apart pure theoretical aspects of nonadiabatic superconductors, we classified major classes of superconductors (including, elements, A-15 and Heusler alloys, Laves phases, intermetallics, noncentrosymmetric compounds, cuprates, pnictides, highly-compressed hydrides and oxygen, and magic-angle twisted bilayer graphene) by the strength of nonadiabaticity (for which the ratio of the Debye temperature to the Fermi temperature, $T{_\theta}/T{_F}$, is used as a criterion for the nonadiabaticity) versus the superconducting transition temperature, $T{_c}$. The discussion of this classification scheme and its relation to other known classification counterparts is given.",2212.02396v3 2023-12-29,"Effect of Point Defects and Lattice Distortions on the Structural, Electronic, and Magnetic properties of Co$_2$MnAl Heusler alloy","The effects of various point defects and lattice distortions on the structural, electronic, and magnetic properties of Co$_2$MnAl alloy are investigated using density functional theory calculations. For the point defects, six types of binary antisites, three types of ternary antisites, and three kinds of vacancies have been simulated with different disorder degrees, up to a maximum of 12.50%. For the lattice distortions, cubic strain within -10% $\leq$$\Delta{V/V_0}$$\leq$ 10% (corresponding to 5.50\r{A} $\leq$ a $\leq$5.88\r{A}) and tetragonal distortions with 0.5$\leq$$\textit{c/a}$$\leq$1.5 at three different unit-cell volumes - $\textit{V}_0$ and ($\textit{V}_0$$\pm5$%$\textit{V}_0$) have been considered. The Co$_{Al}$ and Mn$_{Al}$ binary antisite disordered structures (namely, Co$_{2.0625}$MnAl$_{0.9375}$, Co$_{2.125}$MnAl$_{0.875}$, Co$_2$Mn$_{1.0625}$Al$_{0.9375}$ and Co$_2$Mn$_{1.125}$Al$_{0.875}$) and (Co$_{Al}$+Mn$_{Al}$) ternary antisite disordered structure (Co$_{2.0625}$Mn$_{1.0625}$Al$_{0.875}$) exhibit perfect half-metallicity. The rest of the antisite disorders have a marginal effect on the half-metallic properties of Co$_2$MnAl, along with high spin polarization ($\textit{P}$ $\geq$ 70%) and nearly same magnetization ($\textit{M$_s$}$) as that for ideal structure. Conversely, the vacancy defects significantly affect the electronic and magnetic properties. The cubic strained structures exhibit high $\textit{P}$ and constant $\textit{M$_s$}$. Under negative strain within -10% $\leq$$\Delta{V/V_0}$$\leq$ -7% (for 5.50\r{A} $\leq$ a $\leq$ 5.58\r{A}), the strained structures have perfect half-metallicity. On the other hand, tetragonal distortions lead to significant degradation in half-metallic behavior, except for small distortion values $\Delta{c/a}$, irrespective of their volume.",2312.17545v1 2002-10-22,First-principles calculations of spin spirals in Ni2MnGa and Ni2MnAl,"We report here non-collinear magnetic configurations in the Heusler alloys Ni2MnGa and Ni2MnAl which are interesting in the context of the magnetic shape memory effect. The total energies for different spin spirals are calculated and the ground state magnetic structures are identified. The calculated dispersion curves are used to estimate the Curie temperature which is found to be in good agreement with experiments. In addition, the variation of the magnetic moment as a function of the spiral structure is studied. Most of the variation is associated with Ni, and symmetry constraints relevant for the magnetization are identified. Based on the calculated results, the effect of the constituent atoms in determining the Curie temperature is discussed.",0210482v1 2003-07-04,Detection of weak-order phase transitions in ferromagnets by ac resistometry,"It is shown that ac resistometry can serve as an effective tool for the detection of phase transitions, such as spin reorientation or premartensitic phase transitions, which generally are not disclosed by dc resistivity measurement. Measurement of temperature dependence of impedance, $Z(T)$, allows one to unmask the anomaly, corresponding to a weak-order phase transition. The appearance of such an anomaly is accounted for by a change in the effective permeability $\mu$ of a sample upon the phase transition. Moreover, frequency dependence of $\mu$ makes it possible to use the frequency of the applied ac current as an adjusting parameter in order to make this anomaly more pronounced. The applicability of this method is tested for the rare earth Gd and Heusler alloy Ni$_2$MnGa.",0307096v1 2003-11-13,"Structural, magnetic and transport properties of thin films of the Heusler alloy Co2MnSi","Thin films of Co2MnSi have been grown on a-plane sapphire substrates from three elemental targets by dc magnetron co-sputtering. These films are single phase, have a strong (110) texture and a saturation magnetization of 4.95 uB/formula unit at 10 K. Films grown at the highest substrate temperature of 715 K showed the lowest resistivity (47 uOhm cm at 4.2 K) and the lowest coercivity (18 Oe). The spin polarization of the transport current was found to be of the order of 54% as determined by point contact Andreev reflection spectroscopy. A decrease in saturation magnetization with decreasing film thickness and different transport behaviour in thinner films indicate a graded disorder in these films grown on non-lattice matched substrates.",0311316v1 2004-03-09,Resistivity and Thermopower of Ni2.19Mn0.81Ga,"In this paper, we report results of the first studies on the thermoelectric power (TEP) of the magnetic heusler alloy Ni$_{2.19}$Mn$_{0.81}$Ga. We explain the observed temperature dependence of the TEP in terms of the crystal field (CF) splitting and compare the observed behavior to that of the stoichiometric system Ni$_2$MnGa. The resistivity as a function of temperature of the two systems serves to define the structural transition temperature, T$_M$, which is the transition from the high temperature austenitic phase to low temperatures the martensitic phase. Occurrence of magnetic (Curie-Weiss) and the martensitic transition at almost the same temperature in Ni$_{2.19}$Mn$_{0.81}$Ga has been explained from TEP to be due to changes in the density of states (DOS) at the Fermi level.",0403232v2 2004-08-10,Towards half-metallic interfaces: the Co$_2$CrAl/InP contacts,"Although the interest on half-metallic Heusler alloys, susceptible to be used in spintronic applications, has considerably grown, their interfaces with semiconductors show very low spin-polarization. I identify mechanisms which can keep the high spin-polarization at the interface (more than 80% of the electrons at the Fermi level are of majority spin) although the half-metallicity is lost. The large enhancement of the Cr moment at the interface between a CrAl terminated Co$_2$CrAl(001) spacer and the InP(001) semiconductor weakens the effect of the interface states resulting in this high spin-polarization. On the other hand the Co$_2$CrAl/InP interfaces made up by a Co layer and either an In or a P one show a severe decrease of the Co spin moment but Cr in the subinterface layer is bulklike and the resulting spin-polarization is similar to the CrAl-based interfaces.",0408204v3 2004-09-13,Interface properties of the NiMnSb/InP and NiMnSb/GaAs contacts,"We study the electronic and magnetic properties of the interfaces between the half-metallic Heusler alloy NiMnSb and the binary semiconductors InP and GaAs using two different state-of-the-art full-potential \textit{ab-initio} electronic structure methods. Although in the case of most NiMnSb/InP(001) contacts the half-metallicity is lost, it is possible to keep a high degree of spin-polarization when the interface is made up by Ni and P layers. In the case of the GaAs semiconductor the larger hybridization between the Ni-$d$ and As-$p$ orbitals with respect to the hybridization between the Ni-$d$ and P-$p$ orbitals destroys this polarization. The (111) interfaces present strong interface states but also in this case there are few interfaces presenting a high spin-polarization at the Fermi level which can reach values up to 74%.",0409333v1 2004-12-22,Investigation of the growth and magnetic properties of highly oriented films of the Heusler alloy Co2MnSi on GaAs(001),"Highly (001) oriented thin films of Co2MnSi have been grown on lattice matched GaAs(001) without a buffer layer. Stoichiometric films exhibited a saturation magnetization slightly reduced from the bulk value and films grown at the highest substrate temperature of 689 K showed the lowest resistivity (33 micro.ohm.cm at 4.2 K) and the lowest coercivity (14 Oe). The spin polarization of the transport current was found to be of the order of 55% as determined by point contact Andreev reflection spectroscopy. The reduced magnetization obtained was attributed to the antiferromagnetic Mn2As phase. Twofold in-plane magnetic anisotropy was observed due to the inequivalence of the <110> directions, and this was attributed to the nature of the bonding at the reconstructed GaAs surface.",0412636v1 2005-02-24,Structural and magnetic properties of the (001) and (111) surfaces of the half-metal NiMnSb,"Using the full potential linearised augmented planewave method we study the electronic and magnetic properties of the (001) and (111) surfaces of the half-metallic Heusler alloy NiMnSb from first-principles. We take into account all possible surface terminations including relaxations of these surfaces. Special attention is paid to the spin-polarization at the Fermi level which governs the spin-injection from such a metal into a semiconductor. In general, these surfaces lose the half-metallic character of the bulk NiMnSb, but for the (111) surfaces this loss is more pronounced. Although structural optimization does not change these features qualitatively, specifically for the (111) surfaces relaxations can compensate much of the spin-polarization at the Fermi surface that has been lost upon formation of the surface.",0502597v1 2006-05-15,Vortex fluctuations and freezing of dipolar-coupled granular moments in thin ferromagnetic films,"Below the Curie temperature T_c of a Heusler-alloy film, consisting of densely packed, but exchange-decoupled nanograins, the spontaneous magnetization M_s(T) and static in-plane susceptibility \chi_{||}(T) increase very slowly signalizing a suppression of magnetization fluctuations. The unpredicted variation \chi_{||}(T) ~ G_d^2(T), where G_d ~ M_s^2 is the intergranular dipolar coupling, and also the magnetic freezing observed in the dynamic susceptibility at lower temperatures is quantitatively reproduced by Monte Carlo (MC) simulations with 10^4 dipolar-coupled moments on a disordered triangular lattice. At high temperatures, the MC spin configurations clearly reveal a dense gas of local vortex structures, which at low temperatures condense in regions with stronger disorder. This vortex depletion upon decreasing temperature seems to be responsible for the observed \textit{increase} of the magnetic relaxation time. For weak disorder, the temperature dependence of the MC vorticity and a singularity of the specific heat at T_v=1/2 G_d(T_v)/k_B indicate a thermal transition from a vortex gas to a state with a single vortex center plus linear vortex structures.",0605377v1 2007-11-06,Half-metallic ferromagnets: From band structure to many-body effects,"A review of new developments in theoretical and experimental electronic structure investigations of half-metallic ferromagnets (HMF) is presented. Being semiconductors for one spin projection and metals for another ones, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMF by the peculiarities of their electronic structure and chemical bonding is discussed. Effects of electron-magnon interaction in HMF and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Especial attention is paid to appearance of non-quasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-art electronic calculations for correlated $d$-systems is discussed, and results for specific HMF (Heusler alloys, zinc-blende structure compounds, CrO$_{2},$ Fe$_{3}$O$_{4}$) are reviewed.",0711.0872v1 2008-10-10,Anomalous Magnetic Properties in Ni50Mn35In15,"We present here a comprehensive investigation of the magnetic ordering in Ni50Mn35In15 composition. A concomitant first order martensitic transition and the magnetic ordering occurring in this off-stoichiometric Heusler compound at room temperature signifies the multifunctional character of this magnetic shape memory alloy. Unusual features are observed in the dependence of the magnetization on temperature that can be ascribed to a frustrated magnetic order. It is compelling to ascribe these features to the cluster type description that may arise due to inhomogeneity in the distribution of magnetic atoms. However, evidences are presented from our ac susceptibility, electrical resistivity and dc magnetization studies that there exists a competing ferromagnetic and antiferromagnetic order within crystal structure of this system. We show that excess Mn atoms that substitute the In atoms have a crucial bearing on the magnetic order of this compound. These excess Mn atoms are antiferromagnetically aligned to the other Mn, which explains the peculiar dependence of magnetization on temperature.",0810.1850v1 2008-11-14,Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study,"The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with unique properties for future applications. Band structure calculations predict exclusively majority bands at the Fermi level, thus indicating {100%} spin polarization there. As one thinks about applications and the design of functional materials, the influence of chemical disorder in these materials must be considered. The magnetization, spin polarization, and electronic structure are expected to be sensitive to structural and stoichiometric changes. In this contribution, we report on an investigation of the spin-dependent electronic structure of NiMnSb. We studied the influence of chemical disorder on the unoccupied electronic density of states by use of the ab-initio Coherent Potential Approximation method. The theoretical analysis is discussed along with corresponding spin-resolved Appearance Potential Spectroscopy measurements. Our theoretical approach describes the spectra as the fully-relativistic self-convolution of the matrix-element weighted, orbitally resolved density of states.",0811.2300v1 2009-01-21,Ruderman-Kittel-Kasuya-Yosida spin density oscillations: impact of the finite radius of the exchange interaction,"A non-interacting electron gas on a one-dimensional ring is considered at finite temperatures. The localized spin is embedded at some point on the ring and it is assumed that the interaction between this spin and the electrons is the exchange interaction being the basis of the Ruderman-Kittel-Kasuya-Yosida indirect exchange effect. When the number of electrons is large enough, it turns out that any small but finite interaction radius value can always produce an essential change of the spin density oscillations in comparison with the zero interaction radius traditionally used to model the Ruderman-Kittel-Kasuya-Yosida effect.",0901.3339v2 2009-12-04,A new spin-functional MOSFET based on magnetic tunnel junction technology: pseudo-spin-MOSFET,"We fabricated and characterized a new spin-functional MOSFET referred to as a pseudo-spin-MOSFET (PS-MOSFET). The PS-MOSFET is a circuit using an ordinary MOSFET and magnetic tunnel junction (MTJ) for reproducing functions of spin-transistors. Device integration techniques for a bottom gate MOSFET using a silicon-on-insulator (SOI) substrate and for an MTJ with a full-Heusler alloy electrode and MgO tunnel barrier were developed. The fabricated PS-MOSFET exhibited high and low transconductance controlled by the magnetization configurations of the MTJ at room temperature. This is the first observation of spin-transistor operations for spin-functional MOSFETs.",0912.0835v1 2010-02-19,Interplay of magnetic order and Jahn-Teller distortion in a model with strongly correlated electron system,"The Hubbard model has been employed successfully to understand many aspects of correlation driven physical properties, in particular, the magnetic order in itenerant electron systems. In some systems such as Heusler alloys, manganites etc., it is known that, in addition to magnetic order, distortion induced by Jahn-Teller(J-T) effect also exists. In this paper, based on two-fold degenerate Hubbard model, the influence of magnetic order on J-T distortion is investigated. The electron correlation is treated using a spectral density approach and J-T interaction is added to the model. We find that magnetic order and structural distortion coexist at low temperature $T$ for a certain range of electron correlation strength $U$, J-T coupling strength $G$ and band occupation $n$. At T=0, for a given $n$ and $U$, magnetic order is present but distortion appears only for a $G$ larger than a critical value. We also studied the temperature dependence of lattice strain and magnetization choosing a $G$ close to the critical value.",1002.3718v2 2010-02-28,A Frequency-Controlled Magnetic Vortex Memory,"Using the ultra low damping NiMnSb half-Heusler alloy patterned into vortex-state magnetic nano-dots, we demonstrate a new concept of non-volatile memory controlled by the frequency. A perpendicular bias magnetic field is used to split the frequency of the vortex core gyrotropic rotation into two distinct frequencies, depending on the sign of the vortex core polarity $p=\pm1$ inside the dot. A magnetic resonance force microscope and microwave pulses applied at one of these two resonant frequencies allow for local and deterministic addressing of binary information (core polarity).",1003.0158v1 2010-03-26,Tunnel effect in ferromagnetic half-metal Co$_2$CrAl-superconductor heterostructures,"Ferromagnetic half-metal Co$_2$CrAl films and tunnel contacts Co$_2$CrAl - insulator (I) - Pb are fabricated and investigated. It is found that the normalized differential conductivity $\sigma ^{\rm FS} $ of such tunnel junctions with low resistance is larger than the normalized differential conductivity $\sigma ^{\rm NS} $ of known normal metal - I - superconductor type tunnel junctions. It is shown that the observed increase in $\sigma ^{\rm FS} $ is caused by the accumulation of spin polarized electrons in a superconductor and can be used for estimating the spin polarization degree $P$ in ferromagnets. This method shows that $P$ of L2$_1$-type ordered Co$_2$CrAl Heusler alloy films at $T = 4.2{\rm K}$ is close to 1.",1003.5093v1 2012-04-03,Effect of interfacial strain on spin injection and spin polarization of Co2CrAl/NaNbO3/Co2CrAl magnetic tunneling junction,"First-principles calculations were carried out to investigate interfacial strain effects on spin injection and spin polarization of a magnetic tunnel junction consisting of half-metallic full-Heusler alloy Co2CrAl and ferroelectric perovskite NaNbO3. Spin-dependent coherent tunneling was calculated within the framework of non-equilibrium Green's function technique. Both spin polarization and tunnel magnetoresistance (TMR) are affected by the interfacial strain but their responses to compressive and tensile strains are different. Spin polarization across the interface is fully preserved under a compressive strain due to stronger coupling between interfacial atoms, whereas a tensile strain significantly enhances interface states and lead to substantial drops in spin polarization and TMR.",1204.0611v1 2012-06-11,Residual disorder and diffusion in thin Heusler alloy films,"Co2FeSi/GaAs(110) and Co2FeSi/GaAs(111)B hybrid structures were grown by molecular-beam epitaxy and characterized by transmission electron microscopy (TEM) and X-ray diffraction. The films contained inhomogeneous distributions of ordered L2_1 and B2 phases. The average stoichiometry was controlled by lattice parameter measurements, however diffusion processes lead to inhomogeneities of the atomic concentrations and the degradation of the interface, influencing long-range order. An average long-range order of 30-60% was measured by grazing-incidence X-ray diffraction, i.e. the as-grown Co2FeSi films were highly but not fully ordered. Lateral inhomogeneities of the spatial distribution of long-range order in Co2FeSi were found using dark-field TEM images taken with superlattice reflections.",1206.2242v1 2012-08-15,Two-dimensional electron-gas-like charge transport at magnetic Heusler alloy-SrTiO$_3$ interface,"We report remarkably low residual resistivity, giant residual resistivity ratio, free-electron-like Hall resistivity and high mobility ($\approx$ 10$^4$ cm$^2$V$^{-1}$s$^{-1}$) charge transport in epitaxial films of Co$_2$MnSi and Co$_2$FeSi grown on (001) SrTiO$_3$. This unusual behavior is not observed in films deposited on other cubic oxide substrates of comparable lattice parameters. The scaling of the resistivity with thickness of the films allow extraction of interface conductance, which can be attributed to a layer of oxygen vacancies confined within 1.9 nm of the interface as revealed by atomically resolved electron microscopy and spectroscopy. The high mobility transport observed here at the interface of a fully spin polarized metal is potentially important for spintronics applications.",1208.3099v2 2013-03-29,Formation of double ring patterns on Co2MnSi Heusler alloy thin film by anodic oxidation under scanning probe microscope,"Double ring formation on Co2MnSi (CMS) films is observed at electrical breakdown voltage during local anodic oxidation (LAO) using atomic force microscope (AFM). Corona effect and segregation of cobalt in the vicinity of the rings is studied using magnetic force microscopy and energy dispersive spectroscopy. Double ring forma-tion is attributed to the interaction of ablated material with the induced magnetic field during LAO. Steepness of forward bias transport characteristics from the unperturbed region of the CMS film suggest a non equilibrium spin contribution. Such mesoscopic textures in magnetic films by AFM tip can be potentially used for memory storage applications.",1303.7470v2 2013-05-30,Evolution of ferromagnetic and spin-wave resonances with crystalline order in thin films of full-Heusler alloy Co2MnSi,"We report the evolution of magnetic moment as well as magnetic anisotropy with crystalline order in Co$_2$MnSi thin films grown on $(100)$ MgO by pulsed laser deposition. The films become more ordered as the annealing temperature ($T_A$) increases from 400 to 600 $^0$C. The extent of \emph{L}$2_1$ ordering in the films annealed at 600 $^0$C is $\approx 96%$. The static magnetization measurements by vibrating sample magnetometry shows a maximum moment of 4.95 $\mu_B$ per formula unit with low coercivity ($H_C$ $\approx$ 65 Oe) in the films annealed at 600 $^0$C. A rigorous analysis of the azimuthal and polar angle dependent ferromagnetic resonance (FMR) measured at several temperatures allows determination of various anisotropy fields relevant to our system as a function of $T_A$. Finally, we have evaluated the exchange stiffness constant down to 100 K using spin wave modes in FMR spectra. We have also estimated the exchange energies as well as stiffness constant by varying the lattice parameter \emph{ab-initio} using the Korringa-Kohn-Rostoker method.",1305.7048v1 2013-07-14,"Effect of annealing on the magnetic, magnetocaloric and magnetoresistance properties of Ni-Co-Mn-Sb melt spun ribbons","The structural, magnetic, magnetocaloric and magnetotransport properties of Ni46Co4Mn38Sb12 melt spun ribbons have been systematically investigated. The partially ordered B2 phase of the as-spun ribbon transforms to fully ordered L21 phase upon annealing, which signifies a considerable change of the atomic ordering in the system. The presence of atomic disorder in the as-spun ribbon gives rise to a higher martensitic transition temperature and a lower magnetization as compared to the bulk sample. However, annealing the ribbons helps in regaining the bulk properties to a large extent. Significant changes in magnetocaloric effect, exchange bias and magnetoresistance have been observed between the as-spun and the annealed ribbons, indicating the role of atomic ordering on the functional as well as fundamental properties in the Heusler system. Importantly, the study shows that one can reduce the hysteresis loss by preparing melt spun alloys and subjecting them to appropriate annealing conditions, which enable them to become practical magnetic refrigerants.",1307.3776v1 2013-07-14,In-plane and out of plane magnetic properties in Ni46Co4Mn38Sb12 Heusler alloys ribbons,"Magnetic, magnetocaloric and exchange bias properties have been systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic field along (IP) and perpendicular (OP) to the ribbon plane. From the thermo-magnetization curves, the sharpness of the martensitic transition is observed to be nearly the same for both IP and OP ribbons. The thermomagnetic irreversibility region is found to be larger in the OP ribbon at 500 Oe, indicating that the magnetic anisotropy is larger in this case. The OP ribbon shows the Hopkinson maximum at 500 Oe, both for the FCC and ZFC modes. The magnetization curve for IP ribbon shows a faster approach to saturation, compared to the OP ribbon. Isothermal magnetic entropy change at 50 kOe has been found to be nearly same for both the ribbons. At 5 K the coercivity and exchange bias values are larger for the OP ribbon. Crystallographic texturing of the ribbons and its effect in the easy magnetization direction are found to be the reason behind the differences between the two ribbons.",1307.3778v1 2014-01-31,First-principles calculation of the instability leading to giant inverse magnetocaloric efects,"The structural and magnetic properties of functional Ni-Mn-Z (Z = Ga, In, Sn) Heusler alloys are studied by first-principles and Monte Carlo methods. The \textit{ab initio} calculations give a basic understanding of the underlying physics which is associated with the strong competition of ferro- and antiferromagnetic interactions with increasing chemical disorder. The resulting $d$-electron orbital dependent magnetic ordering is the driving mechanism of magnetostructural instability which is accompanied by a drop of magnetization governing the size of the magnetocaloric effect. The thermodynamic properties are calculated by using the \textit{ab initio} magnetic exchange coupling constants in finite-temperature Monte Carlo simulations, which are used to accurately reproduce the experimental entropy and adiabatic temperature changes across the magnetostructural transition.",1401.8148v1 2014-02-28,The fate of half-metallicity near interfaces: the case of NiMnSb/MgO and NiMnSi/MgO,"The electronic and magnetic properties of the interfaces between the half-metallic Heusler alloys NiMnSb, NiMnSi and MgO have been investigated using first-principles density-functional calculations with projector augmented wave potentials generated in the generalized gradient approximation. In the case of the NiMnSb/MgO (100) interface the half-metallicity is lost, whereas the MnSb/MgO contact in the NiMnSb/MgO (100) interface maintains a substantial degree of spin polarization at the Fermi level ($\sim 60$%). Remarkably, the NiMnSi/MgO (111) interface shows 100% spin polarization at the Fermi level, despite considerable distortions at the interface, as well as rather short Si/O bonds after full structural optimization. This behavior markedly distinguishes NiMnSi/MgO (111) from the corresponding NiMnSb/CdS and NiMnSb/InP interfaces.",1403.0889v1 2014-03-14,Investigation on Mn$_{3-δ}$Ga/MgO interface for magnetic tunneling junctions,"The Mn$_3$Ga Heusler compound and related alloys are the most promising materials for the realization of spin-transfer-torque switching in magneto tunneling junctions. Improved performance can be achieved by high quality interfaces in these multilayered structured devices. In this context, the interface between Mn$_{1.63}$Ga and MgO is of particular interest because of its spin polarization properties in tunneling junctions. We performed a chemical characterization of the MgO/Mn$_{1.63}$Ga junction by hard x-ray photoelectron spectroscopy (HAXPES). The experiment indicated the formation of Ga-O bonds at the interface and evidenced changes in the local environment of Mn atoms in the proximity of the MgO film. In addition, we show that the insertion of a metallic Mg-layer interfacing the MgO and Mn--Ga film strongly suppresses the oxidation of gallium.",1403.3556v4 2014-11-03,Importance of two current model in understanding the electronic transport behavior of inverse Heusler alloy: Fe 2 CoSi,"Here we explore the applicability of the two current model in understanding the transport behavior of Fe 2 CoSi compound by using the first principles calculations in combination with the Boltzmann transport theory. The spin-unpolarized calculation shows large density of states (DOS) at Fermi level (E F) and is unable to provide the correct temperature dependence of transport coefficients. The spin-polarised calculation shows reduced DOS at the E F in the spin-up channel, whereas spin-dn channel have almost zero DOS at the E F . The absolute value of Seebeck coefficient in the spin-up channel shows linear increment with the temperature and in the spin-dn channel it varies non-linearly. The electrical conductivity also shows non-linear temperature dependence in both the spin channels whereas, the electronic thermal conductivity shows linear temperature dependence. The values of transport coefficients and their temperature dependence obtained by using the two current model are found to be in fairly good agreement with the experimental data. Present work clearly suggests the importance of two current model in understanding the transport properties of the compound.",1411.0367v1 2015-05-29,Strain behavior and lattice dynamics in Ni50Mn35In15,"The lattice dynamics in the polycrystalline shape-memory Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$ has been studied by means of resonant ultrasound spectroscopy (RUS). RUS spectra were collected in a frequency range $100-1200$ kHz between 10 and 350 K. Ni$_{50}$Mn$_{35}$In$_{15}$ exhibits a ferromagnetic transition at 313 K in the austenite and a martensitic transition at 248 K accompanied by a change of the magnetic state. Furthermore it displays a antiferromagnetic to ferromagnetic transition within the martensitic phase. We determined the temperature dependence of the shear modulus and the acoustic attenuation of Ni$_{50}$Mn$_{35}$In$_{15}$ and compared it with magnetization data. Following the structural softening, which accompanies the martensitic transition as a pretransitional phenomenon, a strong stiffening of the lattice is observed at the martensitic magneto-structural transition. Only a weak magnetoelastic coupling is evidenced at the Curie temperatures both in austenite and martensite phase. The large acoustic damping in the martensitic phase compared with the austenitic phase reflects the motion of the twin walls, which freezes out in the low temperature region.",1505.08090v1 2015-06-29,Magnetization and magneto-transport studies on Fe$_2$VAl$_{1-x}$Si$_x$,"We report on magnetoresistance, Hall and magnetization measurements of Fe2VAl1-xSix Heusler compounds for x= 0.005, 0.015, 0.02. There is a systematic change in the temperature coefficient of resistance (TCR) from negative to positive as the Si composition is increased. The Hall co-efficient shows that the carriers are electron like and the carrier density increases with Si concentration. Resistance measurements under magnetic field indicate a decreasing behavior under the application of magnetic field at low temperature region (T< 60 K), suggesting the suppression of scattering by magnetic field. Temperature and field dependent magnetization measurements did not show any significant change apart from the fact that the presence of super paramagnetic (SPM) cluster and its ordering at low temperatures. Arrott plot analysis of magnetization versus field also indicates the magnetic ordering with applied field below 60 K.",1506.08516v1 2015-07-22,An indirect magnetic approach for determining entropy change in first-order magnetocaloric materials,"Taking into account the phase fraction during transition for the first-order magnetocaloric materials, an improved isothermal entropy change determination has been put forward based on the Clausius-Clapeyron (CC) equation. It was found that the isothermal entropy change value evaluated by our method is in excellent agreement with those determined from the Maxwell-relation (MR) for Ni-Mn-Sn Heusler alloys, which usually presents a weak field-induced phase transforming behavior. In comparison with MR, this method could give rise to a favorable result derived from few thermomagnetic measurements. More importantly, we can eliminate the isothermal entropy change overestimation derived from MR, which always exists in the cases of Ni-Co-Mn-In and MnAs systems with a prominent field-induced transition. These results confirmed that such a CC-equation-based method is quite practical and superior to the MR-based ones in eliminating the spurious spike and reducing measuring cost.",1507.06133v2 2015-10-09,Better Band Gaps with Asymptotically Corrected Local Exchange Potentials,"We formulate a spin-polarized van Leeuwen and Baerends (vLB) correction to the local density approximation (LDA) exchange potential [Phys. Rev. A 49, 2421 (1994)] that enforces the ionization potential (IP) theorem following Stein et al. [Phys. Rev. Lett. 105, 266802 (2010)]. For electronic-structure problems, the vLB-correction replicates the behavior of exact-exchange potentials, with improved scaling and well-behaved asymptotics, but with the computational cost of semi-local functionals. The vLB+IP corrections produces large improvement in the eigenvalues over that from LDA due to correct asympotic behavior and atomic shell structures, as shown on rare-gas, alkaline-earth, zinc-based oxides, alkali-halides, sulphides, and nitrides. In half-Heusler alloys, this asymptotically-corrected LDA reproduces the spin-polarized properties correctly, including magnetism and half-metallicity. We also considered finite-sized systems [e.g., ringed boron-nitirde (B$_{12}$N$_{12}$) and graphene (C$_{24}$)] to emphasize the wide applicability of the method.",1510.02688v3 2016-05-13,Spin injection into multilayer graphene from highly spin-polarized Co2FeSi Heusler alloy,"We demonstrate electrical spin injection into multilayer graphene (MLG) in a lateral spin valve device from a highly spin-polarized Co2FeSi (CFS) Huesler electrode. Exfoliated MLG was transferred onto pre-patterned epitaxial CFS wires grown on an Si(111) substrate by a polymer-based transfer method. This method enabled us to fabricate multiple single-crystal CFS electrodes in contact with MLG. Electrical spin injection from CFS to MLG was detected through non-local magnetoresistance (MR) measurement. A non-local spin signal of 430 ohm was observed; this is the largest value among all reported non-local MR values in graphene-based devices.",1605.04213v1 2016-08-31,Spin polarization ratios of resistivity and density of states estimated from anisotropic magnetoresistance ratio for nearly half-metallic ferromagnets,"We derive a simple relational expression between the spin polarization ratio of resistivity, $P_\rho$, and the anisotropic magnetoresistance ratio $\Delta \rho/\rho$, and that between the spin polarization ratio of the density of states at the Fermi energy, $P_{\rm DOS}$, and $\Delta \rho/\rho$ for nearly half-metallic ferromagnets. We find that $P_\rho$ and $P_{\rm DOS}$ increase with increasing $|\Delta \rho/\rho|$ from 0 to a maximum value. In addition, we roughly estimate $P_\rho$ and $P_{\rm DOS}$ for a Co$_2$FeGa$_{0.5}$Ge$_{0.5}$ Heusler alloy by substituting its experimentally observed $\Delta \rho/\rho$ into the respective expressions.",1608.08888v1 2016-10-12,Spin injection and detection up to room temperature in Heusler~alloy/$n$-GaAs spin valves,"We have measured the spin injection efficiency and spin lifetime in Co$_2$FeSi/$n$-GaAs lateral nonlocal spin valves from 20 to 300 K. We observe large ($\sim$40 $\mu$V) spin valve signals at room temperature and injector currents of $10^3~$A/cm$^2$, facilitated by fabricating spin valve separations smaller than the 1 $\mu$m spin diffusion length and applying a forward bias to the detector contact. The spin transport parameters are measured by comparing the injector-detector contact separation dependence of the spin valve signal with a numerical model accounting for spin drift and diffusion. The apparent suppression of the spin injection efficiency at the lowest temperatures reflects a breakdown of the ordinary drift-diffusion model in the regime of large spin accumulation. A theoretical calculation of the D'yakonov-Perel spin lifetime agrees well with the measured $n$-GaAs spin lifetime over the entire temperature range.",1610.03797v1 2017-03-29,Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Films,"Magnetic skyrmions are topological spin structures having immense potential for energy efficient spintronic devices. However, observations of skyrmions at room temperature are limited to patterned nanostructures. Here, we report the observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film heterostructures at room temperature and in zero external magnetic field employing magnetic force microscopy. The skyrmions are observed in a trilayer structure comprised of heavy metal (HM)/ferromagnet (FM)/Oxide interfaces which result in strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as evidenced by Brillouin light scattering measurements, in agreement with the results of micromagnetic simulations. We also emphasize on room temperature observation of multiple skyrmions which can be stabilized for suitable choices of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These results open up a new paradigm for designing room temperature spintronic devices based on skyrmions in FM continuous thin films.",1703.10224v1 2017-07-27,Reversible tuning of magnetocaloric Ni-Mn-Ga-Co films on ferroelectric PMN-PT substrates,"Tuning functional properties of thin caloric films by mechanical stress is currently of high interest. In particular, a controllable magnetisation or transition temperature is desired for improved usability in magnetocaloric devices. Here, we present results of epitaxial magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg$_{1/3}$Nb$_{2/3}$)$_{0.72}$Ti$_{0.28}$O$_3$ (PMN-PT) substrates. Utilizing X-ray diffraction measurements, we demonstrate that the strain induced in the substrate by application of an electric field can be transferred to the thin film, resulting in a change of the lattice parameters. We examined the consequences of this strain on the magnetic properties of the thin film by temperature and electric field dependent measurements. We did not observe a change of martensitic transformation temperature but a reversible change of magnetisation within the austenitic state, which we attribute to the intrinsic magnetic instability of this metamagnetic Heusler alloy.",1707.08839v1 2017-08-03,Room-temperature spin transport in n-Ge probed by four-terminal nonlocal measurements,"We demonsrtate electrical spin injection and detection in $n$-type Ge ($n$-Ge) at room temperature using four-terminal nonlocal spin-valve and Hanle-effect measurements in lateral spin-valve (LSV) devices with Heusler-alloy Schottky tunnel contacts. The spin diffusion length ($\lambda$$_{\rm Ge}$) of the Ge layer used ($n \sim$ 1 $\times$ 10$^{19}$ cm$^{-3}$) at 296 K is estimated to be $\sim$ 0.44 $\pm$ 0.02 $\mu$m. Room-temperature spin signals can be observed reproducibly at the low bias voltage range ($\le$ 0.7 V) for LSVs with relatively low resistance-area product ($RA$) values ($\le$ 1 k$\Omega$$\mu$m$^{2}$). This means that the Schottky tunnel contacts used here are more suitable than ferromagnet/MgO tunnel contacts ($RA \ge$ 100 k$\Omega$$\mu$m$^{2}$) for developing Ge spintronic applications.",1708.00962v1 2017-09-19,Effect of Co substitution on Ni$_{2}$MnGe Heusler alloy: ab initio study,"Ab initio calculations shown that the Co substitution instead of Ni in Ni$_{2}$MnGe with the L2$_{1}$ crystallographic structure leads to a decrease of the lattice constant and an increase of the total magnetic moment of the Ni$_{2-x}$Co$_{x}$MnGe compounds. The Mn(B) has the largest local moment above $3~\mu_{B}$ coupled parallel to moments on the Ni(A,C) and Co(A,C), which are found in the ranges of $0.19\div0.26~\mu_{B}$ for Ni(A,C) and $1.03\div0.97~\mu_{B}$ for Co(A,C) for studied range of $x$. Using the results stemming from the total energy calculations, the values of bulk modulus and its pressure derivatives are estimated according to the Murnaghan EOS.",1709.06490v1 2017-12-06,First-principles investigation of magnetocrystalline anisotropy oscillations in Co$_{2}$FeAl/Ta heterostructures,"We report first-principles investigations of magnetocrystalline anisotropy energy (MCAE) oscillations as a function of capping layer thickness in Heusler alloy Co\textsubscript{2}FeAl/Ta heterostructures. Substantial oscillation is observed in FeAl-interface structure. According to $k$-space and band-decomposed charge density analyses, this oscillation is mainly attributed to the Fermi-energy-vicinal quantum well states (QWS) which are confined between Co\textsubscript{2}FeAl/Ta interface and Ta/vacuum surface. The smaller oscillation magnitude in the Co-interface structure can be explained by the smooth potential transition at the interface. These findings clarify that MCAE in Co\textsubscript{2}FeAl/Ta is not a local property of the interface and that the quantum well effect plays a dominant role in MCAE oscillations of the heterostructures. This work presents the possibility of tuning MCAE by QWS in capping layers, and paves the way for artificially controlling magnetic anisotropy energy in magnetic tunnel junctions.",1712.02139v2 2018-06-03,"Chiral Magnetic Skyrmions with Arbitrary Topological Charge (""skyrmionic sacks"")","We show that continuous and spin-lattice models of chiral ferro- and antiferromagnets provide the existence of an infinite number of stable soliton solutions of any integer topological charge. A detailed description of the morphology of new skyrmions and the corresponding energy dependencies are provided. The considered model is general, and is expected to predict a plethora of particle-like states which may occur in various chiral magnets including atomic layers, e.g., PdFe/Ir(111), rhombohedral GaV$_4$S$_8$ semiconductor, B20-type alloys as Mn$_{1-x}$Fe$_x$Ge, Mn$_{1-x}$Fe$_x$Si, Fe$_{1-x}$Co$_x$Si, Cu$_2$OSeO$_3$, acentric tetragonal Heusler compounds.",1806.00782v2 2019-01-24,Effect of secondary LuNiSn phase on thermoelectric properties of half-Heusler alloy LuNiSb,"We report on the high-temperature (350 K room temperature, RT) and type II films (Gd and Ni$_{2}$MnSn with T$_{C}$ $\approx$ RT). We study the effect of laser fluence and pulse width for single Gaussian laser pulses and the effect of metal film thickness on magnetization dynamics. Spectral dynamics show that broadband spin waves up to 24 THz could be generated by all-optical manipulation of magnetization in these nanofilms.",2005.03493v1 2016-03-30,Magnetic Interactions and Electronic Structure of Pt$_{2}$Mn$_{1-x}$Y$_{x}$Ga (Y = Cr and Fe) system : An ab-initio calculation,"First principles density functional theory based calculations have been carried out to predict the effects of Mn replacement by Fe and Cr on electronic as well as magnetic properties of Pt$_{2}$MnGa as well as Ni$_{2}$MnGa. All the materials studied here are predicted to have conventional Heusler alloy structure in their ground state and they are found to be electronically stable on the basis of their respective formation energy. The replacement of Mn by Fe leads to a ferromagnetic ground state whereas in case of Mn replacement by Cr an {\it intra-sublattice} anti-ferromagnetic configuration has been observed to have lower energy. We study the magnetic exchange interaction between the atoms for the materials with ferromagnetic and anti-ferromagnetic configurations to show the effects of Fe and Cr substitution at Mn site on the magnetic interactions of these systems. Detailed analysis of electronic structure in terms of density of states has been carried out to study the effect of substitution.",1603.09139v1 2016-12-22,Type-II Dirac semimetals in the YPd$_2$Sn class,"The Lorentz-invariance-violating Weyl and Dirac fermions have recently attracted intensive interests as new types of particles beyond high-energy physics, and they demonstrate novel physical phenomena such as angle-dependent chiral anomaly and topological Lifshitz transition. Here we predict the existence of Lorentz-invariance-violating Dirac fermions in the YPd$_2$Sn class of Heusler alloys that emerge at the boundary between the electron-like and hole-like pockets in the Brillouin zone, based on the first-principles electronic structure calculations. In combination with the fact that this class of materials was all reported to be superconductors, the YPd$_2$Sn class provides an appropriate platform for studying exotic physical properties distinguished from conventional Dirac fermions, especially for realizing possible topological superconductivity.",1612.07456v1 2017-06-06,Coupling between a charge density wave and magnetism in an Heusler material,"The Prototypical magnetic memory shape alloy Ni$_2$MnGa undergoes various phase transitions as a function of temperature, pressure, and doping. In the low-temperature phases below 260 K, an incommensurate structural modulation occurs along the [110] direction which is thought to arise from softening of a phonon mode. It is not at present clear how this phenomenon is related, if at all, to the magnetic memory effect. Here we report time-resolved measurements which track both the structural and magnetic components of the phase transition from the modulated cubic phase as it is brought into the high-symmetry phase. The results suggest that the photoinduced demagnetization modifies the Fermi surface in regions that couple strongly to the periodicity of the structural modulation through the nesting vector. The amplitude of the periodic lattice distortion, however, appears to be less affected by the demagnetizaton.",1706.01685v1 2019-09-12,Single pulse all-optical toggle switching of magnetization without Gd: The example of Mn2RuxGa,"Energy-efficient control of magnetization without the help of a magnetic field is a key goal of spintronics. Purely heat-induced single-pulse all-optical toggle switching has been demonstrated, but so far only in Gd based amorphous ferrimagnet films. In this work, we demonstrate toggle switching in the half-metallic compensated ferrimagnetic Heusler alloys Mn2RuxGa, which have two crystallographically-inequivalent Mn sublattices. Moreover, we observe the switching at room temperature in samples that are immune to external magnetic fields in excess of 1 T, provided they exhibit compensation above room temperature. Observations of the effect in compensated ferrimagnets without Gd challenges our understanding of all-optical switching. The dynamic behavior indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis for fast optical switching of magnetization and break new ground for engineered materials that can be used for nonvolatile ultrafast switches using ultrashort pulses of light.",1909.05809v2 2020-02-06,Thermal dependence of the mechanical properties of NiTiSn using first-principles calculations and high-pressure X-ray diffraction,"In this work we aim to study the effect of temperature on the mechanical properties of a solid. For this, we have introduced a new first-principles based methodology to obtain the thermal variation of the elastic constants of NiTiSn, a multifunctional Heusler compound. In parallel using X-ray diffraction, we have measured the isothermal bulk modulus at 300~K. The agreement between the calculations and the experiments is within the experimental error bars showing the accuracy of the calculations. Using two other numerical methods, which give all coherent results, we have shown that NiTiSn conserves its very good mechanical properties up to 1500~K. In particular at 700~K (the best working temperature for thermoelectric applications), NiTiSn remains a ductile and robust material making it a compound of choice for applications in which large temperature fluctuations are present.",2002.02161v1 2021-02-22,Suppression of spinodal instability by disorder in an athermal system,"We observed asymmetric critical slowing down and asymmetric dynamical scaling exponent in the superheating and supercooling kinetic processes during the thermally-induced metal-insulator transition of MnNiSn based heusler alloy. During the transition to the insulator phase, the critical-like features get enhanced compared to the transition back to the metal phase. These experimental findings suggest that the metastable phase in the cooling branch of hysteresis has approached close to the spinodal instability. On the other hand, the extended disorder, generated over and above the intrinsic crystal defects during heating, triggers the excess heterogeneous nucleation before reaching the spinodal point. Zero temperature random field Ising model (ZTRFIM) simulation, inscribed for the athermal martensitic transitions, support the argument that the disorder smears the spinodal instabilities as the correlation length is bounded by the average distance between the disorder points.",2102.11347v2 2021-08-19,"IrCrMnZ (Z=Al, Ga, Si, Ge) Heusler alloys as electrode materials for MgO-based magnetic tunneling junctions: A first-principles study","We study IrCrMnZ (Z=Al, Ga, Si, Ge) systems using first-principles calculations from the perspective of their application as the electrode materials of MgO-based MTJs. These materials have highly spin-polarized conduction electrons with partially occupied $\Delta_1$ band, which is important for coherent tunneling in parallel magnetization configuration. The Curie temperatures of IrCrMnAl and IrCrMnGa are very high (above 1300 K) as predicted from mean-field-approximation. The stability of ordered phase against various antisite disorders has been investigated. We discuss here the effect of ""spin-orbit-coupling"" on the electronic structure around Fermi level. Further, we investigate the electronic structure of IrCrMnZ/MgO heterojunction along (001) direction. IrCrMnAl/MgO and IrCrMnGa/MgO maintain half-metallicity even at the MgO interface, with no interfacial states at/around Fermi level in the minority-spin channel. Large majority-spin conductance of IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa is reported from the calculation of ballistic spin-transport property for parallel magnetization configuration. We propose IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa as promising MTJs with a weaker temperature dependence of tunneling magnetoresistance ratio, owing to their very high Curie temperatures.",2108.08501v1 2021-10-26,Giant quadratic magneto-optical response of thin YIG films for sensitive magnetometric experiments,"We report on observation of a magneto-optical effect quadratic in magnetization (Cotton-Mouton effect) in 50 nm thick layer of Yttrium-Iron Garnet (YIG). By a combined theoretical and experimental approach, we managed to quantify both linear and quadratic magneto-optical effects. We show that the quadratic magneto-optical signal in the thin YIG film can exceed the linear magneto-optical response, reaching values of 450 urad that are comparable with Heusler alloys or ferromagnetic semiconductors. Furthermore, we demonstrate that a proper choice of experimental conditions, particularly with respect to the wavelength, is crucial for optimization of the quadratic magneto-optical effect for magnetometry measurement.",2110.13679v1 2022-04-04,Phase-field modeling of paramagnetic austenite-ferromagnetic martensite transformation coupled with mechanics and micromagnetics,"A three-dimensional phase-field model is proposed for simulating the magnetic martensitic phase transformation. The model considers a paramagnetic cubic austenite to ferromagnetic tetragonal martensite transition, as it occurs in magnetic Heusler alloys like Ni2 MnGa, and is based on a Landau 2-3-4 polynomial with temperature dependent coefficients. The paramagnetic-ferromagnetic transition is recaptured by interpolating the micromagnetic energy as a function of the order parameter for the ferroelastic domains. The model is numerically implemented in real space by finite element (FE) method. FE simulations in the martensitic state show that the model is capable to correctly recapture the ferroelastic and -magnetic microstructures, as well as the influence of external stimuli. Simulation results indicate that the paramagnetic austenite to ferromagnetic martensite transition shifts towards higher temperatures when a magnetic field or compressive stress is applied. The dependence of the phase transition temperature shift on the strength of the external stimulus is uncovered as well. Simulation of the phase transition in magnetocaloric materials is of high interest for the development of energy-efficient magnetocaloric cooling devices.",2204.01308v1 2022-10-10,Numerical stability and efficiency of response property calculations in density functional theory,"Response calculations in density functional theory aim at computing the change in ground-state density induced by an external perturbation. At finite temperature these are usually performed by computing variations of orbitals, which involve the iterative solution of potentially badly-conditioned linear systems, the Sternheimer equations. Since many sets of variations of orbitals yield the same variation of density matrix this involves a choice of gauge. Taking a numerical analysis point of view we present the various gauge choices proposed in the literature in a common framework and study their stability. Beyond existing methods we propose a new approach, based on a Schur complement using extra orbitals from the self-consistent-field calculations, to improve the stability and efficiency of the iterative solution of Sternheimer equations. We show the success of this strategy on nontrivial examples of practical interest, such as Heusler transition metal alloy compounds, where savings of around 40% in the number of required cost-determining Hamiltonian applications have been achieved.",2210.04512v2 2022-12-15,Resonant and off-resonant magnetoacoustic waves in epitaxial Fe$_3$Si/GaAs hybrid structures,"Surface acoustic waves (SAWs) provide an efficient dynamical coupling between strain and magnetization in micro/nano-metric devices. Using a hybrid device composed of a piezoelectric, GaAs, and a ferromagnetic Heusler alloy thin film, Fe$_3$Si, we are able to quantify the amplitude of magnetoacoustic waves generated with SAWs via magnetic imaging in an X-ray photoelectron microscope. The cubic anisotropy of the sample together with a low damping coefficient allows for the observation of resonant and non-resonant magnetoelastic coupling. Additionally, via micromagnetic simulation, we verify the experimental behavior and quantify the magnetoelastic shear strain component in Fe$_3$Si that appears to be very large ($b_2=14\times 10^6$ J/m$^3$), much larger than the one found in Nickel.",2212.07994v1 2022-12-21,"Electronic and phonon contributions to the Thermoelectric properties of newly discovered half-Heusler alloys XHfPb (X= Ni, Pd, and Pt)","In this work we calculate the thermoelectric figure of merit of XHfPb (X= Ni, Pd, and Pt) by computing the both the power factor and the lattice thermal conductivity by first principles. We make reasonable approximations: we use the Constant Relaxation Time Approximation (CRTA) to compute the electron transport contribution and the modified Debye-Callaway model to calculate the thermal lattice conductivity. We also report the dielectric properties of these semiconductors and the mode Gr\""uneisen parameters. Not surprisingly we find that the average Gr\""uneisen coefficient correlates with the tehrmal conductivity. Next, we consider a realistic relaxation time $\tau$ and carrier concentration $n$ from experimental data on ZrHfPb and obtain the figure of merit $ZT$ as a function of temperature. Our main finding is that despite the Pt is isoelectronic with Ni and Pd, the $ZT$ of PtHfPb is larger and behaves differently from the other two materials, suggesting that PtHfPb is better suited for high temperature thermoelectric generators.",2212.10848v1 2023-01-24,Ru$_{2-x}$Mn$_{1+x}$Al thin films,"The cubic Heusler alloy Ru$_{2-x}$Mn$_{1+x}$Al is grown in thin film form on MgO and MgAl$_2$O$_4$ substrates. It is a highly spin-polarised ferrimagnetic metal, with weak magnetocrystalline anisotropy. Although structurally and chemically similar to $\text{Mn}_2\text{Ru}_x\text{Ga}$, it does not exhibit ferrimagnetic compensation, or large magneto galvanic effects. The differences are attributed to a combination of atomic order and the hybridisation with the group 13 element Al or Ga. The spin polarisation is around 50 to 60 %. There is a gap in the density of states just above the Fermi level in fully ordered compounds.",2301.10148v2 2023-03-21,Unveiling the magnetic structure and phase transition of Cr$_2$CoAl using neutron diffraction,"We report the detailed analysis of temperature dependent neutron diffraction pattern of the Cr$_2$CoAl inverse Heusler alloy and unveil the magnetic structure up to the phase transition as well as its fully compensated ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using the space group I$\bar4${\it m}2 confirm the inverse tetragonal structure over the large temperature range from 100~K to 900~K. The refinement of the magnetic phase considering the wave vector $k=$ (0, 0, 0) reveals the ferrimagnetic nature of the sample below 730$\pm$5~K. This transition temperature is obtained from empirical power law fitting of the variation in the ordered net magnetic moment and intensity of (110) peak as a function of temperature. The spin configuration of the microscopic magnetic structure suggests the nearly fully compensated ferrimagnetic behavior where the magnetic moments of Cr2 are antiparallel with respect to the Cr1, and Co moments. Moreover, the observed anomaly in the thermal expansion and lattice parameters at 730$\pm$5~K suggest that the distortion in crystal structure may play an important role in the magnetic phase transition.",2303.11869v1 2023-05-15,Magnetic order and electronic transport properties in the Mn$_3$Al compound: the role of the structural state,"Electronic transport and magnetic properties of bulk and rapid melt quenched samples of the Mn$_3$Al Heusler alloy were studied. A correlation between the magnetic and structural states was established. For a cast sample, there is no ferromagnetic moment, and the behavior of the magnetic susceptibility (break at low temperatures and the Curie-Weiss law with high values of the paramagnetic Curie temperature) indicates a frustrated antiferromagnetic state. At the same time, for a rapid melt quenched sample, a ferrimagnetic state is observed with a moment close to compensation. The results of measurements of the electrical resistivity and the Hall effect evidence as well in favor of the implementation of these magnetic states.",2305.08646v1 2024-03-20,Record-high Anomalous Ettingshausen effect in a micron-sized magnetic Weyl semimetal on-chip cooler,"Solid-state cooling devices offer compact, quiet, reliable and environmentally friendly solutions that currently rely primarily on the thermoelectric (TE) effect. Despite more than two centuries of research, classical thermoelectric coolers suffer from low efficiency which hampers wider application. In this study, the less researched Anomalous Ettingshausen effect (AEE), a transverse thermoelectric phenomenon, is presented as a new approach for on-chip cooling. This effect can be boosted in materials with non-trivial band topologies as demonstrated in the Heusler alloy $\text{Co}_2\text{MnGa}$. Enabled by the high quality of our material, in situ scanning thermal microscopy experiments reveal a record-breaking anomalous Ettingshausen coefficient of $-2.1$~mV in $\mu$m-sized on-chip cooling devices at room temperature. A significant 44\% of the effect is contributed by the intrinsic topological properties, in particular the Berry curvature of $\text{Co}_2\text{MnGa}$, emphasising the unique potential of magnetic Weyl semimetals for high-performance spot cooling in nanostructures.",2403.13598v1 2021-11-04,Influence of microstructure on the application of Ni-Mn-In Heusler compounds for multicaloric cooling using magnetic field and uniaxial stress,"Novel multicaloric cooling utilizing the giant caloric response of Ni-Mn-based metamagnetic shape-memory alloys to different external stimuli such as magnetic field, uniaxial stress and hydrostatic pressure is a promising candidate for energy-efficient and environmentally-friendly refrigeration. However, the role of microstructure when several external fields are applied simultaneously or sequentially has been scarcely discussed in literature. Here, we synthesized ternary Ni-Mn-In alloys by suction casting and arc melting and analyzed the microstructural influence on the response to magnetic fields and uniaxial stress. By combining SEM-EBSD and stress-strain data, a significant effect of texture on the stress-induced martensitic transformation is revealed. It is shown that a <001> texture can strongly reduce the critical transformation stresses. The effect of grain size on the material failure is demonstrated and its influence on the magnetic-field-induced transformation dynamics is investigated. Temperature-stress and temperature-magnetic field phase diagrams are established and single caloric performances are characterized in terms of ${\Delta}{s_T}$ and ${\Delta}{T_{ad}}$. The cyclic ${\Delta}{T_{ad}}$ values are compared to the ones achieved in the multicaloric exploiting-hysteresis cycle. It turns out that a suction-cast microstructure and the combination of both stimuli enables outstanding caloric effects in moderate external fields which can significantly exceed the single caloric performances. In particular for Ni-Mn-In, the maximum cyclic effect in magnetic fields of 1.9 T is increased by more than 200 % to -4.1 K when a moderate sequential stress of 55 MPa is applied. Our results illustrate the crucial role of microstructure for multicaloric cooling using Ni-Mn-based metamagnetic shape-memory alloys.",2111.03092v2 2022-12-26,In plane reorientation induced single laser pulse magnetization reversal in rare-earth based multilayer,"Single Pulse All Optical Helicity Independent Switching (AO-HIS) represents the ability to reverse the magnetic moment of a nanostructure using a femtosecond single laser pulse. It is an ultrafast method to manipulate magnetization without the use of any applied field. Since the first switching experiments carried on GdFeCo ferrimagnetic systems, single pulse AO-HIS has been restricted for a while to Gd-based alloys or Gd/FM bilayers where FM is a ferromagnetic layer. Only recently has AO-HIS been extended to a few other materials: MnRuGa ferrimagnetic Heusler alloys and Tb/Co multilayers with a very specific range of thickness and composition. Here, we demonstrate that single pulse AO-HIS observed in Tb/Co results from a different mechanism than the one for Gd based samples and that it can be obtained for a large range of rare earth-transition metal (RE-TM) multilayers, making this phenomenon much more general. Surprisingly, in this large family of (RE-TM) multilayer systems, the threshold fluence for switching is observed to be independent of the pulse duration, up to at least 12 ps. Moreover, at high laser intensities, concentric ring domain structures are induced, unveiling multiple fluence thresholds. These striking switching features, which are in contrast to those of AO-HIS in GdFeCo alloys, concomitant with the demonstration of an in-plane reorientation of the magnetization, point towards an intrinsic precessional reversal mechanism. Our results allow expanding the variety of materials with tunable magnetic properties that can be integrated in complex heterostructures and provide a pathway to engineer materials for future applications based on all-optical control of magnetic order.",2212.13279v1 2005-04-20,First-principles study of thin magnetic transition-metal silicide films on Si(001),"In order to combine silicon technology with the functionality of magnetic systems, a number of ferromagnetic (FM) materials have been suggested for the fabrication of metal/semiconductor heterojunctions. In this work, we present a systematic study of several candidate materials in contact with the Si surface. We employ density-functional theory calculations to address the thermodynamic stability and magnetism of both pseudomorphic CsCl-like $M$Si ($M$=Mn, Fe, Co, Ni) thin films and Heusler alloy $M_2$MnSi ($M$=Fe, Co, Ni) films on Si(001). Our calculations show that Si-termination of the $M$Si films is energetically preferable during epitaxy since it minimizes the energetic cost of broken bonds at the surface. Moreover, we can explain the calculated trends in thermodynamic stability of the $M$Si thin films in terms of the $M$-Si bond-strength and the $M$ 3d orbital occupation. From our calculations, we predict that ultrathin MnSi films are FM with sizable spin magnetic moments at the Mn atoms, while FeSi and NiSi films are nonmagnetic. However, CoSi films display itinerant ferromagnetism. For the $M_2$MnSi films with Heusler-type structure, the MnSi termination is found to have the highest thermodynamic stability. In the FM ground state, the calculated strength of the effective coupling between the magnetic moments of Mn atoms within the same layer approximately scales with the measured Curie temperatures of the bulk $M_2$MnSi compounds. In particular, the Co$_2$MnSi/Si(001) thin film has a robust FM ground state as in the bulk, and is found to be stable against a phase separation into CoSi/Si(001) and MnSi/Si(001) films. Hence this material is of possible use in FM-Si heterojunctions and deserves further experimental investigations.",0504515v2 2017-08-25,Topological superconductivity of spin-3/2 carriers in a three-dimensional doped Luttinger semimetal,"We investigate topological Cooper pairing, including gapless Weyl and fully gapped class DIII superconductivity, in a three-dimensional doped Luttinger semimetal. The latter describes effective spin-3/2 carriers near a quadratic band touching and captures the normal-state properties of the 227 pyrochlore iridates and half-Heusler alloys. Electron-electron interactions may favor non-$s$-wave pairing in such systems, including even-parity $d$-wave pairing. We argue that the lowest energy $d$-wave pairings are always of complex (e.g., $d + i d$) type, with nodal Weyl quasiparticles. This implies $\varrho(E) \sim |E|^2$ scaling of the density of states (DoS) at low energies in the clean limit, or $\varrho(E) \sim |E|$ over a wide critical region in the presence of disorder. The latter is consistent with the $T$-dependence of the penetration depth in the half-Heusler compound YPtBi. We enumerate routes for experimental verification, including specific heat, thermal conductivity, NMR relaxation time, and topological Fermi arcs. Nucleation of any $d$-wave pairing also causes a small lattice distortion and induces an $s$-wave component; this gives a route to strain-engineer exotic $s+d$ pairings. We also consider odd-parity, fully gapped $p$-wave superconductivity. For hole doping, a gapless Majorana fluid with cubic dispersion appears at the surface. We invent a generalized surface model with $\nu$-fold dispersion to simulate a bulk with winding number $\nu$. Using exact diagonalization, we show that disorder drives the surface into a critically delocalized phase, with universal DoS and multifractal scaling consistent with the conformal field theory (CFT) SO($n$)${}_\nu$, where $n \rightarrow 0$ counts replicas. This is contrary to the naive expectation of a surface thermal metal, and implies that the topology tunes the surface renormalization group to the CFT in the presence of disorder.",1708.07825v2 2016-12-18,Heusler 4.0: Tunable Materials,"Heusler compounds are a large family of binary, ternary and quaternary compounds that exhibit a wide range of properties of both fundamental and potential technological interest. The extensive tunability of the Heusler compounds through chemical substitutions and structural motifs makes the family especially interesting. In this article we highlight recent major developments in the field of Heusler compounds and put these in the historical context. The evolution of the Heusler compounds can be described by four major periods of research. In the latest period, Heusler 4.0 has led to the observation of a variety of properties derived from topology that includes: topological metals with Weyl and Dirac points; a variety of non-collinear spin textures including the very recent observation of skyrmions at room temperature; and giant anomalous Hall effects in antiferromagnetic Heuslers with triangular magnetic structures. Here we give a comprehensive overview of these major achievements and set research into Heusler materials within the context of recent emerging trends in condensed matter physics.",1612.05947v2 2004-06-05,Role of shuffles and atomic disorder in Ni-Mn-Ga,"We report results of \textit{ab-initio} calculations of the ferromagnetic Heusler alloy Ni-Mn-Ga. Particular emphasis is placed on the stability of the low temperature tetragonal structure with $c/a = 0.94$. This structure cannot be derived from the parent L2$_1$ structure by a simple homogeneous strain associated with the soft elastic constant $C'$. In order to stabilise the tetragonal phase, one has to take into account shuffles of atoms, which form a wave-like pattern of atomic displacements with a well defined period (modulation). While the modulation is related to the soft acoustic [110]-TA$_2$ phonon mode observed in Ni$_2$MnGa, we obtain additional atomic shuffles, which are related to acoustic-optical coupling of the phonons in Ni$_2$MnGa. In addition, we have simulated an off-stoichiometric systems, in which 25 % of Mn atoms are replaced by Ni. The energy of this structure also exhibits a local minimum at $c/a = 0.94$. This allows us to conclude that both shuffles and atomic disorder stabilize the $c/a = 0.94$ structure. In both cases the stability seems to be associated with a dip in the minority-spin density of states (DOS) at the Fermi level, being related to the formation of hybrid states of Ni-\textit{d} and Ga-\textit{p} minority-spin orbitals.",0406139v1 2011-02-10,An effective quantum parameter for strongly correlated metallic ferromagnets,"The correlated motion of electrons in multi-orbital metallic ferromagnets is investigated in terms of a realistic Hubbard model with {\cal N}-fold orbital degeneracy and arbitrary intra- and inter-orbital Coulomb interactions U and J using a Goldstone-mode-preserving non-perturbative scheme. An effective quantum parameter '\hbar'=\frac{U^2+({\cal N}-1)J^2}{(U+({\cal N}-1)J)^2} is obtained which determines, in analogy with 1/S for quantum spin systems and 1/N for the N-orbital Hubbard model, the strength of correlation-induced quantum corrections to magnetic excitations. The rapid suppression of this quantum parameter with Hund's coupling J, especially for large {\cal N}, provides fundamental insight into the phenomenon of strong stabilization of metallic ferromagnetism by orbital degeneracy and Hund's coupling. This approach is illustrated for the case of ferromagnetic iron and the half metallic Heusler alloy Co_2 Mn Si. For realistic values for iron, the calculated spin stiffness and Curie temperature values obtained are in quantitative agreement with measurements. Significantly, the contribution of long wavelength modes is shown to yield a nearly ~25% reduction in the calculated Curie temperature. Finally, an outline is presented for extending the approach to generic multi-band metallic ferromagnets including realistic band-structure features of non-degenerate orbitals and inter-orbital hopping as obtained from LDA calculations.",1102.2115v1 2011-10-10,"Ab-initio calculation of effective exchange interactions, spin waves, and Curie temperature in L2_1- and L1_2-type local moment ferromagnets","Employing first-principles electronic structure calculations in conjunction with the frozen-magnon method we study the effective exchange interactions and spin waves in local moment ferromagnets. As prototypes we have chosen three L2$_1$-type full Heusler alloys Cu$_2$MnAl, Ni$_2$MnSn and Pd$_2$MnSn, and the L1$_2$-type XPt$_3$ compounds with X= V, Cr and Mn. We have also included CoPt$_3$ which is a usual ferromagnet. In all compounds due to the large spatial separation ($\sim 4$ \AA) of the magnetic transition metal atoms, the 3\textit{d} states belonging to different atoms overlap weakly and as a consequence the exchange coupling is indirect, mediated by the \textit{sp} electrons. Calculated effective exchange parameters are long range and show RKKY-type oscillations. The spin-wave dispersion curves are in reasonable agreement with available experimental data. Using the calculated exchange parameters we have estimated the Curie temperatures within both the mean-field and the random-phase approximations. In local moment ferromagents deviations of the estimated Curie temperature with respect to the available experimental data occur when the ground-state electronic structure calculations overestimate the values of the spin magnetic moments as in VPt$_3$.",1110.2156v1 2013-10-23,Magnetoelastic coupling induced magnetic anisotropy in Co$_2$(Fe/Mn)Si thin films,"The influence of epitaxial strain on uniaxial magnetic anisotropy of Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on (001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is susceptible to tune by varying the thickness of the films on STO, while on MgO the films show in-plane easy axis for magnetization (\overrightarrow{M}) irrespective of their thickness. A variational analysis of magnetic free energy functional within the Stoner-Wohlfarth coherent rotation model with out-of-plane uniaxial anisotropy for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant $\approx$ (12.22$\pm$0.07)$\times 10^{-6}$ and (2.02$\pm$0.06)$\times 10^{-6}$, in addition to intrinsic magnetocrystalline anisotropy $\approx$ -1.72$\times 10^{6}$ erg/cm$^{3}$ and -3.94$\times 10^{6}$ erg/cm$^{3}$ for CFS and CMS, respectively. The single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane orientation of magnetization with the decreasing film thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The distinct behaviour of \overrightarrow{M} in the films with lower thickness on STO is attributed to strain-induced tetragonal distortion.",1310.6204v1 2014-12-02,"Structural, electrical and magnetic properties of nanostructured Mn2Ni1.6Sn0.4 melt spun ribbons","Nanocrystalline ribbons of inverse Heusler alloy Mn2Ni1.6Sn0.4 have been synthesised by melt spinning of the arc melted bulk precursor. The single phase ribbons crystallize into a cubic structure and exhibit very fine crystallite size of < 2 nm. Temperature dependent magnetization (M-T) measurements reveal that austenite (A)-martensite (M) phase transition begins at T~248 K and finishes at T~238 K during cooling cycle and these values increase to T~267 K and T~259 K while warming. In cooling cycle, the A-phase shows ferromagnetic (FM) ordering with a Curie temperature T~267 K, while both the FM-antiferromagnetic (AFM) and M-transitions occur at T~242 K. The M-phase undergoes FM transition at T~145 K. These transitions are also confirmed by temperature dependent resistivity measurements. The observed hysteretic behaviour of magnetization and resistivity in the temperature regime spanned by the A-M transition is a manifestation of the first order phase transition. Magnetization and susceptibility data also provide unambiguous evidence in favour of spin glass . The scaling of the glass freezing temperature (Tf) with frequency, extracted from the frequency dependent AC susceptibility measurements, confirms the existence of canonical spin glass at T<145 K. The occurrence of canonical spin glass has been explained in terms of the nanostructuring modified interactions between the FM correlations in the martensitic phase and the coexisting AFM.",1412.0859v1 2015-01-16,Direct measurement of the magnetic anisotropy field in Mn--Ga and Mn--Co--Ga Heusler films,"The static and dynamic magnetic properties of tetragonally distorted Mn--Ga based alloys were investigated. Static properties are determined in magnetic fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film, the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is increased to 1~T. Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency extrapolated to zero-field is found to be 125~GHz with a Gilbert damping, $\alpha$, of 0.019. The anisotropy field is determined from both SQUID and TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of 0.81~MJ/m$^3$. Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film, pulsed magnetic fields up to 60~T are used to determine the field strength required to saturate the film in the plane. For this, the extraordinary Hall effect was employed as a probe of the local magnetisation. By integrating the reconstructed in--plane magnetisation curve, the effective anisotropy energy density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.",1501.03973v1 2015-11-25,Accelerated screening of thermoelectric materials by first-principles computations of electron-phonon scattering,"Recent discovery of new materials for thermoelectric energy conversion is enabled by efficient prediction of materials' performance from first-principles, without empirically fitted parameters. The novel simplified approach for computing electronic transport properties is described, which achieves good accuracy and transferability while greatly reducing complexity and computation cost compared to the existing methods. The first-principles calculations of the electron-phonon coupling demonstrate that the energy dependence of the electron relaxation time varies significantly with chemical composition and carrier concentration, suggesting that it is necessary to go beyond the commonly used approximations to screen and optimize materials' composition, carrier concentration, and microstructure. The new method is verified using high accuracy computations and validated with experimental data before applying it to screen and discover promising compositions in the space of half-Heusler alloys. By analyzing data trends the effective electron mass is identified as the single best general descriptor determining material's performance. The Lorenz number is computed from first principles and the universality of the Wiedemann-Franz law in thermoelectrics is discussed.",1511.08115v7 2017-08-03,Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co$_2$FeAl/MgO interface upon annealing,"We investigate thickness series of films of the Heusler alloy Co$_2$FeAl in order to study the effect of annealing on the interface with a MgO layer and on the bulk magnetic properties. Our results reveal that while the perpendicular interface anisotropy constant $K^{\perp}_{\rm S}$ is zero for the as-deposited samples, its value increases with annealing up to a value of $1.14\, \pm \,0.07$~mJ/m$^2$ for the series annealed at 320$^{\rm o}$C and of $2.07\, \pm \,0.7$~mJ/m$^2$ for the 450$^{\rm o}$C annealed series owing to a strong modification of the interface during the thermal treatment. This large value ensures a stabilization of a perpendicular magnetization orientation for a thickness below 1.7~nm. The data additionally shows that the in-plane biaxial anisotropy constant has a different evolution with thickness in as-deposited and annealed systems. The Gilbert damping parameter $\alpha$ shows minima for all series for a thickness of 40~nm and an absolute minimum value of $2.8\pm0.1\cdot10^{-3}$. The thickness dependence is explained in terms of an inhomogenous magnetization state generated by the interplay between the different anisotropies of the system and by crystalline disorder.",1708.01126v2 2018-10-23,Uncovering the puzzle of complex magnetism in Fe16N2: a first-principles based study,"The electronic structure and magnetic exchange interactions in pure and V-doped Fe16N2 are studied within the framework of density functional theory. The Curie temperatures were obtained with both mean field approximation (MFA) as well as Monte Carlo (MC) calculations. The Curie temperature (TC) for pure Fe16N2 obtained within MFA are significantly larger than the experimental value, suggesting the importance of thermal fluctuations in these systems, and has a resemblance of a lower dimensional spin system. We also briefly discuss about the various possible factors which may lead to a large magnetic moment in this material. The calculated magnetic susceptibility at zero field shows sharp peak at T=TC which resemble a local moment system. From the nature of exchange interactions we try to figure out the nature of the Fesites which might contain localized d-states. Finally, we point out that Fe16N2 can also act as a good spin injector for the III-V semiconductors in addition to its well promised application as permanent magnet since it has a very high spin polarization (larger compared to elemental ferromagnets) as well as quite smaller lattice mismatch (compared to half-metallic Heusler alloys) with the conventional III-V semiconductors such as GaAs or InGaAs. We further demonstrate this through our calculations for Fe16N2(001)/InGaAs(001) heterostructures which shows the non-negligible spin polarization in the semiconductor (InGaAs) region implying a long spin diffusion length.",1810.09818v1 2019-07-24,Nonlinear anomalous Hall effect for Néel vector detection,"Antiferromagnetic (AFM) spintronics exploits the N\'eel vector as a state variable for novel spintronic devices. Recent studies have shown that the field-like and antidamping spin-orbit torques (SOT) can be used to switch the N\'eel vector in antiferromagnets with proper symmetries. However, the precise detection of the N\'eel vector remains a challenging problem. In this letter, we predict that the nonlinear anomalous Hall effect (AHE) can be used to detect the N\'eel vector in most compensated antiferromagnets supporting the antidamping SOT. We show that the magnetic crystal group symmetry of these antiferromagnets combined with spin-orbit coupling produce a sizable Berry curvature dipole and hence the nonlinear AHE. As a specific example, we consider half-Heusler alloy CuMnSb, which N\'eel vector can be switched by the antidamping SOT. Based on density functional theory calculations, we show that the nonlinear AHE in CuMnSb results in a measurable Hall voltage under conventional experimental conditions. The strong dependence of the Berry curvature dipole on the N\'eel vector orientation provides a new detection scheme of the N\'eel vector based on the nonlinear AHE. Our predictions enrich the material platform for studying non-trivial phenomena associated with the Berry curvature and broaden the range of materials useful for AFM spintronics.",1907.10696v3 2020-05-10,Phase stability and the effect of lattice distortions on electronic properties and half-metallic ferromagnetism of Co2FeAl Heusler alloy: An ab initio study,"Density functional theory calculations within the generalized gradient approximation are employed to study the ground state of Co2FeAl. Various magnetic configurations are considered to find out its most stable phase. The ferromagnetic ground state of the Co2FeAl is energetically observed with an optimized lattice constant of 5.70 {\AA}. Thereafter, the system was subjected under uniform and non-uniform strains to see their effects on spin polarization (P) and half-metallicity. The effect of spin orbit coupling is considered in the present study. Half-metallicity (and 100 % P) is only retained under uniform strains started from 0 to +4%, and dropped rapidly from 90% to 16% for the negative strains started from -1% to -6%. We find that the present system is much sensitive under tetragonal distortions as half-metallicity (and 100% P) is preserved only for the cubic case. The main reason for the loss of half-metallicity is due to the shift of the bands with respect to the Fermi level. We also discuss the influence of these results on spintronics devices.",2005.04634v2 2020-06-04,Material Descriptors for the Discovery of Efficient Thermoelectrics,"The predictive performance screening of novel compounds can significantly promote the discovery of efficient, cheap, and non-toxic thermoelectric materials. Large efforts to implement machine-learning techniques coupled to materials databases are currently being undertaken, but the adopted computational methods can dramatically affect the outcome. With regards to electronic transport and power factor calculations, the most widely adopted and computationally efficient method, is the constant relaxation time approximation (CRT). This work goes beyond the CRT and adopts the proper, full energy and momentum dependencies of electron-phonon and ionized impurity scattering, to compute the electronic transport and perform power factor optimization for a group of half-Heusler alloys. Then the material parameters that determine the optimal power factor based on this more advanced treatment are identified. This enables the development of a set of significantly improved descriptors that can be used in materials screening studies, and which offer deeper insights into the underlying nature of high performance thermoelectric materials. We have identified $n_v$$\epsilon_r$ / $D_o^2m_{cond}$ as the most useful and generic descriptor, a combination of the number of valleys, the dielectric constant, the conductivity effective mass, and the deformation potential for the dominant electron-phonon process. The proposed descriptors can accelerate the discovery of new efficient and environment friendly thermoelectric materials in a much more accurate and reliable manner, and some predictions for very high performance materials are presented.",2006.02789v2 2022-06-06,Quantitative theory of magnetic interactions in solids,"In this report we review the method of explicit calculations of interatomic exchange interactions of magnetic materials. This involves exchange mechanisms normally referred to as Heisenberg exchange, Dzyaloshinskii-Moriya interaction and anisotropic symmetric exchange. The connection between microscopic theories of the electronic structure, such as density functional theory or dynamical mean field theory, and interatomic exchange, is given in detail. The different aspects of extracting information for an effective spin Hamiltonian that involves thousands of atoms, from electronic structure calculations considering significantly fewer atoms (1-50) is highlighted. Examples of exchange interactions of a large group of materials is presented, which involves heavy elements of the 3d period, alloys between transition metals, Heusler compounds, multilayer systems as well as overlayers and adatoms on a substrate, transition metal oxides, 4f elements, magnetic materials in two dimensions and molecular magnets. Where possible, a comparison to experimental data is made, that naturally becomes focused on the magnon dispersion. The influence of relativity is reviewed for a few cases, as is the importance of dynamical correlations. Development to theories that handle out of equilibrium conditions is also described here. The review ends with a short description of extensions of the theories behind explicit calculations of interatomic exchange, to non-magnetic situations, e.g. that describe chemical (charge) order and superconductivity.",2206.02415v2 2022-08-09,"Structural, magnetic and transport properties of Co$_2$CrAl epitaxial thin films","We report the physical properties of Co$_2$CrAl Heusler alloy epitaxial thin films grown on single crystalline MgO(001) substrate using pulsed laser deposition technique. The x-ray diffraction pattern in $\theta$-2$\theta$ mode showed the film growth in single phase B2-type ordered cubic structure with the presence of (002) and (004) peaks, and the film oriented along the MgO(001) direction. The $\phi$~scan along the (220) plane confirms the four-fold symmetry and the epitaxial growth relation found to be Co$_2$CrAl(001)[100]$\vert$$\vert$MgO(001)[110]. The thickness of about 12~nm is extracted through the analysis of x-ray reflectivity data. The isothermal magnetization (M--H) curves confirm the ferromagnetic (FM) nature of the thin film having significant hysteresis at 5 and 300~K. From the in-plane M--H curves, the saturation magnetization values are determined to be 2.1~$\mu$$_{\rm B}$/f.u.~at 5~K and 1.6~$\mu$$_{\rm B}$/f.u. at 300~K, which suggests the soft FM behavior in the film having the coercive field $\approx$ 522~Oe at 5~K. The thermo-magnetization measurements at 500~Oe magnetic field show the bifurcation between field-cooled and zero-field-cooled curves below about 100~K. The normalized field-cooled magnetization curve follows the T$^2$ dependency, and the analysis reveal the Curie temperature around 335$\pm$11~K. Moreover, the low-temperature resistivity indicates semiconducting behavior with the temperature, and we find a negative temperature coefficient of resistivity (5.2 $\times$ 10$^{-4}$ /K).",2208.04687v1 2023-01-13,Spin and current transport in the robust half-metallic magnet $c$-CoFeGe,"Spintronics is an emerging form of electronics based on the electrons' spin degree of freedom for which materials with robust half-metallic ferromagnet (HMF) character are very attractive. Here we determine the structural stability, electronic, magnetic, and mechanical properties of the half-Heusler (hH) compound CoFeGe, in particular also in its cubic form. The first-principles calculations suggest that the electronic structure is robust with 100 \% spin polarization at the Fermi level under hydrostatic pressure and uni-axial strain. Both the longitudinal and Hall current polarization are calculated and the longitudinal current polarization ($P_{L}$) is found to be $>99\%$ and extremely robust under uniform pressure and uni-axial strain. The anomalous Hall conductivity (AHC) and Spin Hall conductivity (SHC) of hH cubic CoFeGe (\textit{c}-CoFeGe) are found to be $\sim -100$ S/cm and $\sim 39~\hbar/e$ S/cm, respectively. Moreover, the Curie temperature of the alloy is calculated to be $\sim$524 K with a 3 $\mu_{B}$ magnetic moment. Lastly, the calculated mechanical properties indicate that \textit{c}-CoFeGe is ductile and mechanically stable with a bulk modulus of $\approx$ 154 GPa. Overall, this analysis reveals that cubic CoFeGe is a robust half-metallic ferromagnet and an interesting material for spintronic applications.",2301.05493v1 2023-10-05,Exotic rare earth-based materials for emerging spintronic technology,"The progress in materials science has always been associated with the development of functional materials systems, which enables us to design proof-of-concept devices. To advance further, theoretical predictions of new novel materials and their experimental realization is very important. This chapter reviews the intriguing properties of rare earth-based materials and their applications in spintronics. Spintronics is an emerging technology, which exploits spin degree of freedom of an electron along with its charge property. Discovery of various physical phenomena and their industrial applications in the field of magnetic sensors, magnetic recording and non-volatile memories such as magnetic random access memory (MRAM) and spin-transfer torque (STT) MRAM opens several new directions in this field. Materials with large spin polarization, strong spin-orbit coupling, and tunable electronic and magnetic properties offer an excellent platform for the spintronics technology. Combination of rare earths with other elements such as transition metals show broad range of structural, electronic, and magnetic properties which make them excellent candidates for various spintronic applications. This chapter discusses many such materials ranging from Heusler alloys, topological insulators to two-dimensional ferromagnets and their potential applications. The review gives an insight of how rare-earth materials can play a key role in emerging future technology and have great potential in many new spintronic related applications.",2310.03541v1 2023-11-07,The role of electronic bandstructure shape in improving the thermoelectric power factor of complex materials,"The large variety of complex electronic structure materials and their alloys, offer highly promising directions for improvements in thermoelectric (TE) power factors (PF). Their electronic structure contains rich features, referred to as 'surface complexity', one of them being the highly anisotropic warped energy surface shapes with elongated features and threads in some cases. In this work we use Boltzmann transport simulations to quantify the influence that the shape of the electronic structure energy surfaces has on the PF. Using both analytical ellipsoidal bands, as well as realistic bands from the group of half-Heuslers, we show that band shape complexity alone can offer an advantage to the PF of ~3x in realistic cases. The presence of anisotropic scattering mechanisms such as ionized impurity or polar optical phonon scattering, however, can reduce these improvements by up to ~50%. We show that expressions based on the simple ratio of the density-of-states to the conductivity effective masses, mDOS/mC, together with the number of valleys, can capture the anisotropy shape with a moderate to high degree of correlation. For this, we use a convenient way to extract these masses by mapping the complex bandstructures of materials to parabolic electronic structures, without the need for Boltzmann transport codes. Despite the fact that the PF depends on many parameters, information about the benefits of the band shape alone, would be very useful for identifying and understanding the performance of novel thermoelectric materials.",2311.03935v1 2014-09-23,Guidelines for understanding cubic manganese-rich Heusler compounds,"Manganese-rich Heusler compounds are attracting much interest in the context of spin transfer torque and rare-earth free hard magnets. Here we give a comprehensive overview of the magnetic properties of non-centrosymmetric cubic Mn$_2$-based Heusler materials, which are characterized by an antiparallel coupling of magnetic moments on Mn atoms. Such a ferrimagnetic order leads to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures. In terms of the band structure calculations, we explain the formation of this magnetic order and the Curie temperatures. This overview is intended to establish guidelines for a basic understanding of magnetism in Mn2 -based Heusler compounds.",1409.6532v1 2012-02-17,Insights into ultrafast demagnetization in pseudo-gap half metals,"Interest in femtosecond demagnetization experiments was sparked by Bigot's discovery in 1995. These experiments unveil the elementary mechanisms coupling the electrons' temperature to their spin order. Even though first quantitative models describing ultrafast demagnetization have just been published within the past year, new calculations also suggest alternative mechanisms. Simultaneously, the application of fast demagnetization experiments has been demonstrated to provide key insight into technologically important systems such as high spin polarization metals, and consequently there is broad interest in further understanding the physics of these phenomena. To gain new and relevant insights, we perform ultrafast optical pump-probe experiments to characterize the demagnetization processes of highly spin-polarized magnetic thin films on a femtosecond time scale. Previous studies have suggested shifting the Fermi energy into the center of the gap by tuning the number of electrons and thereby to study its influence on spin-flip processes. Here we show that choosing isoelectronic Heusler compounds (Co2MnSi, Co2MnGe and Co2FeAl) allows us to vary the degree of spin polarization between 60% and 86%. We explain this behavior by considering the robustness of the gap against structural disorder. Moreover, we observe that Co-Fe-based pseudo gap materials, such as partially ordered Co-Fe-Ge alloys and also the well-known Co-Fe-B alloys, can reach similar values of the spin polarization. By using the unique features of these metals we vary the number of possible spin-flip channels, which allows us to pinpoint and control the half metals electronic structure and its influence onto the elementary mechanisms of ultrafast demagnetization.",1202.3874v1 2018-01-06,Development of half metallicity within mixed magnetic phase of Cu$_{1-x}$Co$_x$MnSb alloy,"Cubic Half-Heusler Cu$_{1-x}$Co$_x$MnSb (0 $\leq$ $x$ $\leq$ 0.1) compounds have been investigated both experimentally and theoretically for their magnetic, transport and electronic properties in search of possible half metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest as the end member alloys CuMnSb and CoMnSb are semi metallic (SM) antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM), respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in the carrier concentration at the Fermi level that may lead to half-metallic ground state but there remains a persistent controversy whether the AFM to FM transition occurs simultaneously. Our experimental results reveal that the AFM to FM magnetic transition occurs through a percolation mechanism where Co-substitution gradually suppresses the AFM phase and forces FM polarization around every dopant cobalt. As a result a mixed magnetic phase is realized within this composition range while a nearly HM band structure is developed already at the 10% Co-doping. Absence of T$^2$ dependence in the resistivity variation at low T-region serves as an indirect proof of opening up an energy gap at the Fermi surface in one of the spin channels. This is further corroborated by the ab-initio electronic structure calculations that suggests a nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes produced upon Co doping.",1801.02035v1 2013-01-12,Effect of Co-Fe substitutions on the room-temperature spin polarization in Co_3-xFe_xSi Heusler-compound films,"Using low-temperature molecular beam epitaxy, we study substitutions of Fe atoms for Co ones in Co_3-xFe_xSi Heusler-compound films grown on Si and Ge. Even for the low-temperature grown Heusler-compound films, the Co-Fe atomic substitution at A and C sites can be confirmed by the conversion electron M""ossbauer spectroscopy measurements. As a result, the magnetic moment and room-temperature spin polarization estimated by nonlocal spin-valve measurements are systematically changed with the Co-Fe substitutions. This study experimentally verified that the Co-Fe substitution in Co_3-xFe_xSi Heusler compounds can directly affect the room-temperature spin polarization.",1301.2645v1 2013-01-09,New iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties,"The present work reports on the new soft ferromagnetic Heusler phases Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been predicted to exist in a tetragonal regular Heusler structure. Together with the known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and characterized by powder XRD, 57 Fe M\""ossbauer spectroscopy, SQUID and EDX measurements. In particular M\""ossbauer spectroscopy was used to monitor the degree of local atomic order/disorder and to estimate magnetic moments at the Fe sites from the hyperfine fields. It is shown that in contrast to the previous predictions all the materials except Fe2NiGa basically adopt the inverse cubic Heusler (X-) structure with differing degrees of disorder. The disorder is more enhanced in case of Fe2NiGa, which was predicted as an inverse Heusler phase. The experimental data are compared with results from ab-inito electronic structure calculations on LDA level incorporating the effects of atomic disorder by using the coherent potential approximation (CPA). A good agreement between calculated and experimental magnetic moments is found for the cubic inverse Heusler phases. Model calculations on various atomic configurations demonstrate that antisite disorder tends to enhance the stability of the X-structure. Given the fundamental scientific and technological importance of tetragonal Heusler phases the present results call for further investigations to unravel the factors stabilizing tetragonal Heusler materials.",1301.1988v1 2019-01-28,An Enormous Class of Double Half-Heusler Compounds with Low Thermal Conductivity,"Since their discovery around a century ago, the structure and chemistry of the multi-functional half-Heusler semiconductors have been studied extensively as three component systems. The elemental groups constituting these ternary compounds with the nominal formula XYZ are well established. From the very same set of well-known elements we explore a phase space of quaternary double ($X'X''Y_2Z_2$, $X_2Y'Y''Z_2$, and $X_2Y_2Z'Z''$), triple ($X_2'X''Y_3Z_3$) and quadruple ($X_3'X''Y_4Z_4$) half-Heusler compositions which 10 times larger in size. Using a reliable, first-principles thermodynamics methodology on a selection of 347 novel compositions, we predict 127 new stable quaternary compounds, already more than the 89 reported almost exhaustively for ternary systems. Thermoelectric performance of the state-of-the-art ternary half-Heusler compounds are limited by their intrinsically high lattice thermal conductivity ($\kappa_{L}$). In comparison to ternary half-Heuslers, thermal transport in double half-Heuslers is dominated by low frequency phonon modes with smaller group velocities and limited by disorder scattering. The double half-Heusler composition Ti$_2$FeNiSb$_2$ was synthesized and confirmed to have a significantly lower lattice thermal conductivity (factor of 3 at room temperature) than TiCoSb, thereby providing a better starting point for thermoelectric efficiency optimization. We demonstrate a dependable strategy to assist the search for low thermal conductivity half-Heuslers and point towards a huge composition space for implementing it. Our findings can be extended for systematic discovery of other large families of multi-component intermetallic semiconductors.",1901.09800v1 2013-01-25,All-Heusler giant-magnetoresistance junctions with matched energy bands and Fermi surfaces,"We present an all-Heusler architecture which could be used as a rational design scheme for achieving high spin-filtering efficiency in the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A Co2MnSi/Ni2NiSi/Co2MnSi trilayer stack is chosen as the prototype of such an architecture, of which the electronic structure and magnetotransport properties are systematically investigated by first principles approaches. Almost perfectly matched energy bands and Fermi surfaces between the all-Heusler electrode-spacer pair are found, indicating large interfacial spin-asymmetry, high spin-injection efficiency, and consequently high GMR ratio. Transport calculations further confirms the superiority of the all-Heusler architecture over the conventional Heusler/transition-metal(TM) structure by comparing their transmission coefficients and interfacial resistances of parallel conduction electrons, as well as the macroscopic current-voltage (I-V) characteristics. We suggest future theoretical and experimental efforts in developing novel all-Heusler GMR junctions for the read heads of the next generation high-density hard disk drives (HDDs).",1301.6106v1 2018-02-13,Designing and discovering a new family of semiconducting quaternary Heusler compounds based on the 18-electron rule,"Intermetallic compounds with sizable band gaps are attractive for their unusual properties but rare. Here, we present a new family of stable semiconducting quaternary Heusler compounds, designed and discovered by means of high-throughput \textit{ab initio} calculations based on the 18-electron rule. The 99 new semiconductors reported here adopt the ordered quaternary Heusler structure with the prototype of LiMgSnPd (F$\bar{\mathbf{4}}$3m, No.\,216) and contain 18 valence electrons per formula unit. They are realized by filling the void in the half Heusler structure with a small and electropositive atom, i.e., lithium. These new stable quaternary Heusler semiconductors possess a range of band gaps from 0.3 to 2.5\,eV, and exhibit some unusual properties different from conventional semiconductors, such as strong optical absorption, giant dielectric screening, and high Seebeck coefficient, which suggest these semiconductors have potential applications as photovoltaic and thermoelectric materials. While this study opens up avenues for further exploration of this novel class of semiconducting quaternary Heuslers, the design strategy used herein is broadly applicable across a potentially wide array of chemistries to discover new stable materials.",1802.04875v1 2019-05-09,Half-Heusler Compounds: Promising Materials For Mid-To-High Temperature Thermoelectric Conversion,"Half-Heusler compounds (space group Fm3m) has garnered increasing attention in recent years in the thermoelectric community. Three decades ago, refractory RNiSn half-Heusler compounds (R represents refractory metals such as Hf, Zr, Ti) were found to be narrow-gap semiconductors with large Seebeck coefficients in 100s of micro-volt per Kelvin. Today, half-Heusler (HH) compounds have emerged as promising thermoelectric materials in the intermediate temperature range (400-800oC). HH materials are endowed with good thermal stability and scalability. Thermoelectric n-p modules based on HH materials demonstrate conversion efficiency near 10% and power density output near 9 W/cm2. The objective of this article is to present a historical account of the research and development of thermoelectric half-Heusler compounds. Particularly, there have been notable achievements since 2012 thanks to the emergence of new approaches. As a result, ZT has risen from ~1 to 1.5. The various advances made since the early 1990s to the present are recounted by categorizing half-Heusler materials into three generations (Gen): Gen-1 Gen-2, and Gen-3 HH materials.",1905.03845v1 2013-11-21,Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloy as magnetic electrodes,"HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co2MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for concluding that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co2MnGe film.",1311.5589v1 2019-07-25,Superconducting switching due to triplet component in the Pb/Cu/Ni/Cu/Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$ spin-valve structure,"We report the superconducting properties of the Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$/Cu/Ni/Cu/Pb spin-valve structure which magnetic part comprises the Heusler alloy layer HA = Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$ with a high degree of spin polarization (DSP) of the conduction band and the Ni layer of variable thickness. We obtained that the separation between the superconducting transition curves measured for the parallel ($\alpha = 0^\circ$) and perpendicular ($\alpha = 90^\circ$) orientation of the magnetizations of the HA and Ni layers reaches up to 0.5 K ($\alpha$ is an angle between the magnetization of two ferromagnetic layers). For all studied samples the dependence of the superconducting transition temperature $T_c$ on $\alpha$ demonstrates a deep minimum in the vicinity of the perpendicular configuration of magnetizations. This suggests that the observed minimum and the corresponding full switching effect of the spin valve is caused by the long-range triplet component of the superconducting condensate in the multilayer. Such a large effect can be attributed to a half-metallic nature of the HA layer which in the orthogonal configuration efficiently draws off the spin-polarized Cooper pairs from the space between the HA and Ni layers. Our results indicate a significant potential of the concept of the superconducting spin-valve multilayer comprising a half-metallic ferromagnet recently proposed by A. Singh et al., Phys. Rev. X 5, 021019 (2015) in achieving large values of the switching effect.",1907.11176v2 2021-01-25,Computing and Memory Technologies based on Magnetic Skyrmions,"Solitonic magnetic excitations such as domain walls and, specifically, skyrmionics enable the possibility of compact, high density, ultrafast,all-electronic, low-energy devices, which is the basis for the emerging area of skyrmionics. The topological winding of skyrmion spins affects their overall lifetime, energetics and dynamical behavior. In this review, we discuss skyrmionics in the context of the present day solid state memory landscape, and show how their size, stability and mobility can be controlled by material engineering, as well as how they can be nucleated and detected. Ferrimagnetsnear their compensation points are important candidates for this application, leading to detailed exploration of amorphous CoGd as well as the study of emergent materials such as Mn$_4$N and Inverse Heusler alloys. Along with material properties, geometrical parameters such as film thickness, defect density and notches can be used to tune skyrmion properties, such as their size and stability. Topology, however, can be a double-edged sword, especially for isolated metastable skyrmions, as it brings stability at the cost of additional damping and deflective Magnus forces compared to domain walls. Skyrmion deformation in response to forces also makes them intrinsically slower than domain walls. We explore potential analog applications of skyrmions, including temporal memory at low density, and decorrelator for stochastic computing at a higher density that capitalizes on their interactions. We summarize the main challenges to achieve a skyrmionics technology, including maintaining positional stability with very high accuracy, electrical readout, especially for small ferrimagnetic skyrmions, deterministic nucleation and annihilation, and overall integration with digital circuits with the associated circuit overhead.",2101.09947v4 2021-02-26,Role of chemical disorder in tuning the Weyl points in vanadium doped Co$_2$TiSn,"The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Co-based Heusler alloys. In the present study, we have investigated the role of chemical disorder on the variation of Weyl points in Co\textsubscript{2}Ti\textsubscript{1-x}V\textsubscript{x}Sn magnetic Weyl semimetal candidate. We employ the first principle approach to track the evolution of the nodal lines responsible for the appearance of Weyl node in Co$_2$TiSn as a function of V substitution in place of Ti. By increasing the V concentration in place of Ti, the nodal line moves toward Fermi level and remains at Fermi level around the middle composition. Further increase of the V content, leads shifting of nodal line away from Fermi level. Density of state calculation shows half-metallic behavior for the entire range of composition. The magnetic moment on each Co atom as a function of V concentration increases linearly up to x=0.4, and after that, it starts decreasing. We also investigated the evolution of the Weyl nodes and Fermi arcs with chemical doping. The first-principles calculations reveal that via replacing almost half of the Ti with V, the intrinsic anomalous Hall conductivity increased twice as compared to the undoped composition. Our results indicate that the composition close to the 50\% V doped Co$_2$TiSn, will be an ideal composition for the experimental investigation of Weyl physics.",2102.13389v2 2022-09-30,Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl,"Half-metallic ferromagnets (HMF) are on one of the most promising materials in the field of spintronics due to their unique band structure consisting of one spin sub-band having metallic characteristics along with another sub-band with semiconductor-like behavior. In this work, we report the synthesis of a novel quaternary Heusler alloy FeMnVAl and have studied the structural, magnetic, transport, and electronic properties complemented with first-principles calculations. Among different possible structurally ordered arrangements, the optimal structure is identified by theoretical energy minimization. The corresponding spin-polarized band structure calculations indicates the presence of a half-metallic ferromagnetic ground state. A detailed and careful investigation of the x-ray diffraction data, M\""{o}ssbauer and nuclear magnetic resonance spectra suggest the presence of site-disorder between the Fe and Mn atoms in the stable ordered structure of the system. The magnetic susceptibility measurement clearly establishes a ferromagnetic-like transition below $\sim$213 K. The ${^{57}}$Fe M\""{o}ssbauer spectrometry measurements suggest only the Mn-spins could be responsible for the magnetic order, which is consistent with our theoretical calculation. Surprisingly, the density-functional-theory calculations reveal that the spin-polarization value is almost immunized (92.4\% ${\rightarrow}$ 90.4\%) from the Mn-Fe structural disorder, even when nonmagnetic Fe and moment carrying Mn sites are entangled inseparably. Robustness of spin polarization and half metallicity in the studied FeMnVAl compound comprising structural disorder is thus quite interesting and could provide a new direction to investigate and understand the exact role of disorders on spin polarization in these class of materials, over the available knowledge.",2209.15243v1 2022-11-25,Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi,"The present work aims to address the electronic and magnetic properties of the intermetallic compound GdPd$_2$Bi through a comprehensive study of the structural, magnetic, electrical and thermal transport on a polycrystalline sample, followed by theoretical calculations. Our findings indicate that the magnetic ground state is antiferromagnetic in nature. Magnetotransport data present prominent hysteresis loop hinting a structural transition with further support from specific heat and thermopower measurements, but no such signature is observed in the magnetization study. Temperature dependent powder x-ray diffraction measurements confirm martensitic transition from the high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature (LT) orthorhombic $Pmma$ structure similar to many previously reported shape memory alloys. The HT to LT phase transition is characterized by a sharp increase in resistivity associated with prominent thermal hysteresis. Further, we observe robust Bain distortion between cubic and orthorhombic lattice parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and $c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and elongation along $a$-axis respectively. The sample shows an unusual `non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field as high as 150 kOe. In addition, non-linear field dependence of Hall resistivity is observed below about 30 K, which coincides with the sign change of the Seebeck coefficient. The electronic structure calculations confirm robust metallic states both in the LT and HT phases. It indicates complex nature of the Fermi surface along with the existence of both electron and hole charge carriers. The anomalous transport behaviors can be related to the presence of both electron and hole pockets.",2211.13982v1 2023-01-14,CoRuVSi: A potential candidate for spin semimetal with promising spintronic and thermoelectric properties,"Based on our experimental and theoretical studies, we report the identification of the quaternary Heusler alloy, CoRuVSi as a new member of the recently discovered spin semimetals class. Spin polarised semimetals possess a unique band structure in which one of the spin bands shows semimetallic nature, while the other shows semiconducting/insulating nature. Our findings show that CoRuVSi possesses interesting spintronic and thermoelectric properties. Magnetization data reveal a weak ferri-/antiferro magnetic ordering at low temperatures, with only a very small moment $\sim$ 0.13 $\mu_B$/f.u., attributed to the disorder. Transport results provide strong evidence of semimetallicity dominated by two-band conduction, while magnetoresistance data show a non-saturating, linear, positive, magnetoresistance. Spin polarization measurements using point-contact Andreev reflection spectra reveal a reasonably high spin polarization of $\sim$ 50\%, which matches fairly well with the simulated result. Furthermore, CoRuVSi shows a high thermopower value of $0.7$ $m Watt/ m-K^{2}$ at room temperature with the dominant contribution from the semimetallic bands, rendering it as a promising thermoelectric material as well. Our ab-initio simulation not only confirms a unique semimetallic feature, but also reveals that the band structure hosts a linear band crossing at $\sim$ -0.4 eV below the Fermi level incorporated by a band-inversion. In addition, the observed topological non-trivial features of the band structure is corroborated with the simulated Berry curvature, intrinsic anomalous Hall conductivity and the Fermi surface. The coexistence of many interesting properties relevant for spintronic, topological and thermoelectric applications in a single material is extremely rare and hence this study could promote a similar strategy to identify other potential materials belonging to same class.",2301.05854v1 2018-02-11,"Heusler, Weyl, and Berry","Heusler materials, initially discovered by Fritz Heusler more than a century ago, have grown into a family of more than 1000 compounds, synthesized from combinations of more than 40 elements. These materials show a wide range of properties, but new properties are constantly being found. Most recently, by incorporating heavy elements that can give rise to strong spin-orbit coupling (SOC), non-trivial topological phases of matter, such as topological insulators (TIs), have been discovered in Heusler materials. Moreover, the interplay of symmetry, SOC and magnetic structure allows for the realization of a wide variety of topological phases through Berry curvature design. Weyl points and nodal lines can be manipulated by various external perturbations, which results in exotic properties such as the chiral anomaly, and large anomalous spin and topological Hall effects. The combination of a non-collinear magnetic structure and Berry curvature gives rise a non-zero anomalous Hall effect, which was first observed in the antiferromagnets Mn3Sn and Mn3Ge. Besides this k-space Berry curvature, Heusler compounds with non-collinear magnetic structures also possess real-space topological states in the form of magnetic antiskyrmions, which have not yet been observed in other materials. The possibility of directly manipulating the Berry curvature shows the importance of understanding both the electronic and magnetic structures of Heusler compounds. Together, with the new topological viewpoint and the high tunability, novel physical properties and phenomena await discovery in Heusler compounds.",1802.03771v1 2009-01-12,Screening and Fabrication of Half-Heusler phases for thermoelectric applications,"Half-Heusler phases have gained recently much interest as thermoelectric materials. Screening of possible systems was performed by ab-initio simulation using VASP-software. The energy-versus-Volume (E(V)) curves were calculated and calibrated. For TiCoSb, NbNiSn, FeMoSb the stability of Half-Heusler phase against concurrent crystal structures like TiNiSi, ZrCoAl, ZrBeSi, FeSiV, ZrNiP and Full Heusler was confirmed. However, the thermo-dynamical driving force as calculated from the difference in lattice energies is less than 0.1eV/atom. Hence, the fabrication of Half Heusler phases is a challenge and requires three steps, surface activation of the raw material by ball milling, arc-melting of pressed pellets and finally long-term annealing treatment in a vacuum furnace. On doped TiCoSb specimens, Seebeck coefficients up to 0.1 mV/K, on NiNbSn 0.16 mV/K were measured, although the microstructure was not yet optimized.",0901.1491v3 2013-04-01,First-principles investigation of half-metallic ferromagnetism of half-Heusler compounds XYZ,"We investigate the electronic structure and magnetism of half-Heusler compounds XYZ (X, Y=V, Cr, Mn, Fe, Co and Ni; Z=Al, Ga, In, Si, Ge, Sn, P, As, and Sb) using the ab initio density functional theory calculations. Nine half-metals with half-Heusler structure have been predicted with the half-metallic gap of 0.07-0.67 eV. The calculations show that the formation energies for these nine half-Heusler compounds range from -1.32 to -0.12 eV/f.u., and for CoCrSi, CoCrGe, CoFeGe, CoMnSi, CoMnGe, FeMnGe and FeMnAs, the total energy differences between the half-Heusler structure and the corresponding ground-state structure are small (0.07-0.76 eV/f.u.), thus it is expected that they would be realized in the form of thin films under metastable conditions for spintronic applications. The stability of the half-metallicity of CoCrGe and FeMnAs to the lattice distortion is also investigated in detail.",1304.0344v2 2013-09-27,A first-principles investigation of the thermodynamic and mechanical properties of Ni-Ti-Sn Heusler and half-Heusler materials,"First principles calculations of the vibrational, thermodynamic and mechanical properties of the Ni-Ti-Sn Heusler and half-Heusler compounds have been performed. First, we have calculated the Raman and infrared spectra of NiTiSn, providing benchmark theoretical data directly useful for the assignments of its experimental spectra and clarifying the debate reported in the literature on the assignment of its modes. Then, we have discussed the significant vibrational density-of-states of Ni2TiSn at low-frequencies. These states are at the origin of (i) its smaller free energy, (ii) its higher entropy, and (iii) its lower Debye temperature, with respect to NiTiSn. Finally, we have reported the mechanical properties of the two compounds. In particular, we have found that the half-Heusler compound has the largest stiffness. Paradoxically, its bulk modulus is also the smallest. This unusual behavior has been related to the Ni-vacancies that weaken the structure under isostatic compression. Both compounds show a ductile behavior.",1309.7195v1 2014-10-26,Half-Heusler topological insulators,"Ternary semiconducting or metallic half-Heusler compounds with an atomic composition 1:1:1 are widely studied for their flexible electronic properties and functionalities. Recently, a new material property of half-Heusler compounds was predicted based on electronic structure calculations: the topological insulator. In topological insulators, the metallic surface states are protected from impurity backscattering due to spin-momentum locking. This opens up new perspectives in engineering multifunctional materials. In this article, we introduce half Heusler materials from the crystallographic and electronic structure point of view. We present an effective model Hamiltonian from which the topological state can be derived, notably from a non-trivial inverted band structure. We discuss general implications of the inverted band structure with a focus on the detection of the topological surface states in experiments by reviewing several exemplary materials. Special attention is given to superconducting half-Heusler materials, which have attracted ample attention as a platform for non-centrosymmetric and topological superconductivity.",1410.7011v1 2018-12-04,Recent Advances in Thermoelectric Performance of Half-Heusler Compounds,"Half-Heusler phases (space group F43m, C1b) have recently captured much attention as promising thermoelectric materials for heat-to-electric power conversion in the mid-to-high temperature range. The most studied ones are the RNiSn-type half-Heusler compounds, where R represents refractory metals Hf, Zr, and Ti. These compounds have shown a high-power factor and high-power density, as well as good material stability and scalability. Due to their high thermal conductivity, however, the dimensionless figure of merit (zT) of these materials has stagnated near 1 for a long time. Since 2013, the verifiable ZT of half-Heusler compounds has risen from 1 to near 1.5 for both n- and p-type compounds in the temperature range of 500 to 900 degrees C. In this brief review, we summarize recent advances as well as approaches in achieving the high ZT reported. In particular, we discuss the less-exploited strain-relief effect and dopant resonant state effect studied by the author and his collaborators in more detail. Finally, we point out directions for further development. Keywords: half-Heusler compounds; figure of merit; power density; lattice disorder; dopant resonant states",1812.01709v1 2019-07-31,Perspective: Heusler interfaces -- opportunities beyond spintronics?,"Heusler compounds, in both cubic and hexagonal polymorphs, exhibit a remarkable range of electronic, magnetic, elastic, and topological properties, rivaling that of the transition metal oxides. To date, research on these quantum materials has focused primarily on bulk magnetic and thermoelectric properties or on applications in spintronics. More broadly, however, Heuslers provide a platform for discovery and manipulation of emergent properties at well-defined crystalline interfaces. Here, motivated by advances in the epitaxial growth of layered Heusler heterostructures, I present a vision for Heusler interfaces, focusing on the frontiers and challenges that lie beyond spintronics. The ability to grow these materials epitaxially on technologically important semiconductor substrates, such as GaAs, Ge, and Si, provides a direct path for their integration with modern electronics. Further advances will require new methods to control the stoichiometry and defects to ""electronic grade"" quality, and to control the interface abruptness and ordering at the atomic scale.",1908.00101v1 2021-09-03,"Magnetic Properties of the Heusler Ru$_2$Mn$_X$ ($X$ = Nb, Ta or V) Compounds: Monte Carlo Simulations","In this paper, we have focused on a comparison of the different magnetic properties of the three nano-Heusler Ru$_2$Mn$_X$ (X = Nb, Ta or V) compounds using the Blume-Capel Ising model. The Heusler structures are composed by different mixed spins. In fact, the Ru and Mn atoms are modeled by spin-5/2 and spin-1/2, respectively. While, the X atoms ($X$ = Nb, Ta and V) are represented by the spin-7/2, spin-3/2 and spin-5/2, respectively. This study is carried out by using the Monte Carlo simulations under the Metropolis algorithm. The magnetic behaviors of the three nano-Heusler compounds have been studied and discussed. It is found that Ferrimagnetic to superparamagnetic transitions were observed corresponding to different blocking temperatures. Besides, the effect of the crystal field, the exchange coupling interactions and the external magnetic field have been inspected on the magnetization of each nano-Heusler compound Ru$_2$Mn$_X$ ($X$ = Nb, Ta or V).",2109.01708v1 2005-10-08,Slater-Pauling Rule and Curie-Temperature of Co$_2$-based Heusler compounds,"A concept is presented serving to guide in the search for new materials with high spin polarization. It is shown that the magnetic moment of half-metallic ferromagnets can be calculated from the generalized Slater-Pauling rule. Further, it was found empirically that the Curie temperature of Co$_2$ based Heusler compounds can be estimated from a seemingly linear dependence on the magnetic moment. As a successful application of these simple rules, it was found that Co$_2$FeSi is, actually, the half-metallic ferromagnet exhibiting the highest magnetic moment and the highest Curie temperature measured for a Heusler compound.",0510210v1 2005-11-18,Investigation of Co$_2$FeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment,"This work reports on structural and magnetic investigations of the Heusler compound Co$_2$FeSi. X-Ray diffraction and M\""o\ss bauer spectrometry indicate an ordered $L2_1$ structure. Magnetic measurements by means of X-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment ($6 \mu_B$) and Curie-temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets.",0511462v1 2010-10-11,Half-Heusler Topological Insulators: A First-Principle Study with the Tran-Blaha Modified Becke-Johnson Density Functional,"We systematically investigate the topological band structures of half-Heusler compounds using first-principles calculations. The modified Becke-Johnson exchange potential together with local density approximation for the correlation potential (MBJLDA) has been used here to obtain accurate band inversion strength and band order. Our results show that a large number of half-Heusler compounds are candidates for three-dimensional topological insulators. The difference between band structures obtained using the local density approximation (LDA) and MBJLDA potential is also discussed.",1010.2179v1 2011-03-30,The efficient spin injector scheme based on Heusler materials,"We present the rational design scheme intended to provide the stable high spin-polarization at the interfaces of the magneto-resistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. The present first-principal calculations verify that interface remains half-metallic if the nearest interface layers effectively form a stable Heusler material with the properties intermediate between the surrounding bulk parts. This leads to a simple rule for selecting the proper combinations.",1103.5928v1 2011-09-26,Anomalous Hall effect in the Co-based Heusler compounds Co$_{2}$FeSi and Co$_{2}$FeAl,"The anomalous Hall effect (AHE) in the Heusler compounds Co$_{2}$FeSi and Co$_{2}$FeAl is studied in dependence of the annealing temperature to achieve a general comprehension of its origin. We have demonstrated that the crystal quality affected by annealing processes is a significant control parameter to tune the electrical resistivity $\rho_{xx}$ as well as the anomalous Hall resistivity $\rho_{ahe}$. Analyzing the scaling behavior of $\rho_{ahe}$ in terms of $\rho_{xx}$ points to a temperature-dependent skew scattering as the dominant mechanism in both Heusler compounds.",1109.5498v1 2012-05-02,Superconductivity in the Heusler Family of Intermetallics,"Several physical properties of the superconducting Heusler compounds, focusing on two systems (Y, Lu, Sc)Pd2Sn and APd2M, where A=Hf, Zr and M=Al, In, are summarized and compared. The analysis of the data shows the importance of the electron-phonon coupling for superconductivity in this family. We report the superconducting parameters of YPd2Sn, which has the highest Tc among all known Heusler superconductors.",1205.0433v1 2013-12-10,Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in Half-Heusler and Heusler limits,"Half-Heusler and Heusler compounds have been of great interest for several decades for thermoelectric, magnetic, half-metallic and many other interesting properties. Among these systems, Zr-Ni-Sn compounds are interesting thermoelectrics which can go from semiconducting half-Heusler (HH) limit, ZrNiSn, to metallic Heusler (FH) limit, ZrNi$_2$Sn. Recently Makogo et al. [J. Am. Chem. Soc. 133, 18843 (2011)] found that dramatic improvement in the thermoelectric power factor of HH can be achieved by putting excess Ni into the system. This was attributed to an energy filtering mechanism due to the formation of FH nanostructures in the HH matrix. Using density functional theory we have investigated clustering and nanostructure formation in HH$_{1-x}$FH$_x$ systems near the HH and FH ends and found that excess Ni atoms in HH tend to stay close to each other and form nanoclusters of FH. On the other hand, there is competing interaction between Ni-vacancies in FH which prevent them from forming HH nano clusters. Effects of nano inclusions on the electronic structure at both HH and FH ends will be discussed.",1312.2985v2 2020-10-23,Machine-Learning-based Prediction of Lattice Thermal Conductivity for Half-Heusler Compounds using Atomic Information,"The half-Heusler compound has drawn attention in a variety of fields as a candidate material for thermoelectric energy conversion and spintronics technology. This is because it has various electronic structures, such as semi-metals, semiconductors, and a topological insulator. When the half-Heusler compound is incorporated into the device, the control of high lattice thermal conductivity owing to high crystal symmetry is a challenge for the thermal manager of the device. The calculation for the prediction of lattice thermal conductivity, which is an important physical parameter for controlling the thermal management of the device, requires a calculation cost of several 100 times as much as the usual density functional theory calculation. Therefore, we examined whether lattice thermal conductivity prediction by machine learning was possible on the basis of only the atomic information of constituent elements for thermal conductivity calculated by the density functional theory calculation in various half-Heusler compounds. Consequently, we constructed a machine learning model, which can predict the lattice thermal conductivity with high accuracy from the information of only atomic radius and atomic mass of each site in the half-Heusler type crystal structure. Applying our results, the lattice thermal conductivity for an unknown half-Heusler compound can be immediately predicted. In the future, low-cost and short-time development of new functional materials can be realized, leading to breakthroughs in the search of novel functional materials.",2010.12467v1 2022-05-05,Electronic band structure screening for Dirac points in Heuslers,"The Heusler compounds have provided a playground of material candidates for various technological applications based on their highly diverse and tunable properties, controlled by chemical composition and crystal structure. However, physical exploration of the Heusler chemical space en masse is impossible in practice, hindering the exploration of the chemical composition vs. proprieties relationship. Many of these applications are related to the Heuslers electron transport characteristics, which are embedded in their electronic band structure (EBS). Here we we created a Heuslers dataset using the Materials Project (MP) database -- retrieving both chemical composition and their EBSs. We then used machine learning to develop a model correlating the composition vs. number of Dirac points in the EBS for Heuslers and also other Cubic compounds by identifying said Dirac points using an automated algorithm as well as generating chemical composition and global crystal structure features. Our ML model captures the overall trend, as well as identifies significant electronic and global crystal structure features, however, the ML model suffered from significant variance due to the lack of site specific features. Future work on a methodology for handling atomic site specific features will allow ML models to better match the underlying quantum mechanics governing the properties (also based on site specific properties) and capture the electronic properties in a more generalized approach.",2205.02547v1 1996-07-01,On the Uniqueness of the Papapetrou--Majumdar Metric,"We establish the equality of the ADM mass and the total electric charge for asymptotically flat, static electrovac black hole spacetimes with completely degenerate, not necessarily connected horizon.",9607001v1 2013-01-03,Enhanced thermoelectric performance in TiNiSn-based half-Heuslers,"Thermoelectric figures of merit, ZT > 0.5, have been obtained in arc-melted TiNiSn-based ingots. This promising conversion efficiency is due to a low lattice thermal conductivity, which is attributed to excess nickel in the half-Heusler structure.",1301.0419v1 2023-12-10,"Microstructure Thermal Stability and Superplastic Behavior of Al-6%Mg-0.12%Sc-0.10%Zr-0.10%(Yb, Er, Hf) Ultrafine-Grained Alloys","Superplastic behavior of ultrafine-grained (UFG) Al-6Mg-0.12Sc-0.10Zr-0.1X alloys, where X = Yb (Alloy #1-Yb), Er (Alloy #2-Er), and Hf (Alloy #3-Hf), has been studied. The total content of Sc, Zr, Yb, Er, Hf in the alloys was 0.32 wt.% (0.117-0.118 at.%). The alloys used for benchmarking were Al-6Mg-0.12Sc-0.20Zr (Alloy #4-Zr) and Al-6Mg-0.22Sc-0.10Zr (Alloy #5-Sc). Their UFG microstructure was formed with ECAP. Two different types of deformation behavior during superplasticity were demonstrated. A simultaneous increase in yield stress and elongation to failure during superplastic deformation was discovered. High deformation temperatures were shown to cause a competition between dynamic (strain-induced) grain growth and dynamic recrystallization, leading to a finer grain microstructure. The values of strain hardening factor (n), strain rate sensitivity factor (m), and superplastic deformation threshold stress (Sp) were determined. The impact of the type and concentration of alloying elements on the deformation behavior and dynamic grain growth of Al-6%Mg alloys was investigated. It was established that the maximum elongation to failure in Alloy #1-Yb and Alloy #2-Er is observed at lower deformation temperatures than in Alloy #4-Zr and Alloy #5-Sc. The superplastic properties of Alloy #3-Hf are superior to those of Alloy #4-Zr and Alloy #5-Sc with high content of alloying elements (in at.%). Alloy #1-Yb manifests good elongation to failure (910%) at low temperatures (400 oC). The satisfiability of Hart's criterion for calculating uniform deformation value under superplastic conditions was verified. It was demonstrated that cavitation when pores are formed in large Al3X particles at high temperatures causes early failure of aluminum alloys.",2312.05813v1 2007-02-22,Alloying induced degradation of the absorption edge of InAs_{x}Sb_{1-x},"InAs_{x}Sb_{1-x} alloys show a strong bowing in the energy gap, the energy gap of the alloy can be less than the gap of the two parent compounds. We demonstrate that a consequence of this alloying is a systematic degradation in the sharpness of the absorption edge. The alloy disorder induced band-tail (Urbach tail) characteristics are quantitatively studied for InAs_{0.05}Sb_{0.95}.",0702518v1 2021-06-16,Development of competitive high-entropy alloys using commodity powders,"One of the main drawbacks of the powder metallurgy route for High-Entropy Alloys (HEAs) is the unavailability of fully pre-alloyed powders in the market. Using commodity powders (commercial Ni, Fe and Co base fully pre-alloyed powders, fully available in large quantities and at competitive prices) to produce HEAs presents a completely new and competitive scenario for obtaining viable alloys for high-performance applications.",2106.08576v1 2015-03-09,Magnetic Cluster Expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys,"A Magnetic Cluster Expansion (MCE) model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed using DFT data spanning binary and ternary alloy configurations. Using this MCE model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of alloy compositions, considering both random and ordered alloy structures. In random alloys, the removal of magnetic collinearity constraint reduces the total magnetic moment but does not affect the predicted range of compositions where the alloys adopt low temperature ferromagnetic configurations. During alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace nickel rather than iron atoms. Replacement of Ni by Cr in alloys with high iron content increases the Curie temperature of the alloys. This can be explained by strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr solutions, where the Curie temperature increase, predicted by simulations as a function of Cr concentration, is confirmed by experimental observations.",1503.02481v1 2022-12-20,In vitro evaluation of a novel Mg-Sn-Ge ternary alloy for orthopedic applications,"Magnesium (Mg) and its alloys have attracted considerable attention owing to their excellent biodegradable properties and biocompatibility. Novel Mg-Sn-Ge ternary Mg alloys were developed as potential biodegradable materials for orthopedic applications because of their alloying elements naturally present in humans. The feasibility of these alloys was investigated in terms of mechanical properties, degradation, cytocompatibility, and hemocompatibility. The hardness and elastic modulus of Mg-2Sn-xGe alloys were improved significantly by increasing the Ge content. Among all the alloys, the Mg-2Sn-3Ge alloy displays outstanding biodegradable properties, as evidenced by the electrochemical tests and hydrogen evolution. The degradation products detected on the corroded alloy surfaces weaken at higher Ge levels. The in vitro cytotoxicity assay and hemolysis test showed that the Mg-2Sn-xGe alloys exhibit favorable biocompatibility and hemocompatibility, except for the Mg-2Sn-2Ge alloy.",2212.10296v1 2005-05-25,Semimetalic antiferromagnetism in the half-Heusler compound CuMnSb,"The half-Heusler compound CuMnSb, the first antiferromagnet (AFM) in the Mn-based class of Heuslers and half-Heuslers that contains several conventional and half metallic ferromagnets, shows a peculiar stability of its magnetic order in high magnetic fields. Density functional based studies reveal an unusual nature of its unstable (and therefore unseen) paramagnetic state, which for one electron less (CuMnSn, for example) would be a zero gap semiconductor (accidentally so) between two sets of very narrow, topologically separate bands of Mn 3d character. The extremely flat Mn 3d bands result from the environment: Mn has four tetrahedrally coordinated Cu atoms whose 3d states lie well below the Fermi level, and the other four tetrahedrally coordinated sites are empty, leaving chemically isolated Mn 3d states. The AFM phase can be pictured heuristically as a self-doped Cu$^{1+}$Mn$^{2+}$Sb$^{3-}$ compensated semimetal with heavy mass electrons and light mass holes, with magnetic coupling proceeding through Kondo and/or antiKondo coupling separately through the two carrier types. The ratio of the linear specific heat coefficient and the calculated Fermi level density of states indicates a large mass enhancement $m^*/m \sim 5$, or larger if a correlated band structure is taken as the reference.",0505624v1 2008-08-18,A Ni-based Superconductor: the Heusler Compound ZrNi$_2$Ga,"This work reports on the novel Heusler superconductor ZrNi2Ga. Compared to other nickel-based superconductors with Heusler structure, ZrNi2Ga exhibits a relatively high superconducting transition temperature of Tc=2.9 K and an upper critical field of 1.5 T. Electronic structure calculations show that this relatively high transition temperature is caused by a van Hove singularity, which leads to an enhanced density of states at the Fermi energy. The van Hove singularity originates from a higher order valence instability at the L-point in the electronic structure. The enhanced density of states at the Fermi level was confirmed by specific heat and susceptibility measurements. Although many Heusler compounds are ferromagnetic, our measurements of ZrNi2Ga indicate a paramagnetic state above Tc and could not reveal any traces of magnetic order down to temperatures of at least 0.35 K. We investigated in detail the superconducting state with specific heat, magnetization, and resistivity measurements. The resulting data show the typical behavior of a conventional, weakly coupled BCS (s-wave) superconductor.",0808.2356v1 2010-03-10,Evidence for triplet superconductivity in Josephson junctions with ferromagnetic Cu$_{2}$MnAl-Heusler barriers,"We have studied Josephson junctions with barriers prepared from the Heusler compound Cu$_2$MnAl. In the as-prepared state the Cu$_2$MnAl layers are non ferromagnetic and the critical Josephson current density $j_{c}$ decreases exponentially with the thickness of the Heusler layers $d_{F}$. On annealing the junctions at 240\degree C the Heusler layers develop ferromagnetic order and we observe a dependence $j_{c}(d_{F}$) with $j_{c}$ strongly enhanced and weakly thickness dependent in the thickness range 7.0 nm < $d_{F}$ < 10.6 nm. We attribute this feature to a triplet component in the superconducting pairing function generated by the specific magnetization profile inside thin Cu$_2$MnAl layers.",1003.2082v1 2013-01-23,Data Storage: Review of Heusler Compounds,"In the recent decade, the family of Heusler compounds has attracted tremendous scientific and technological interest in the field of spintronics. This is essentially due to their exceptional magnetic properties, which qualify them as promising functional materials in various data-storage devices, such as giant-magnetoresistance spin valves, magnetic tunnel junctions, and spin-transfer torque devices. In this article, we provide a comprehensive review on the applications of the Heusler family in magnetic data storage. In addition to their important roles in the performance improvement of these devices, we also try to point out the challenges as well as possible solutions, of the current Heusler-based devices. We hope that this review would spark further investigation efforts into efficient incorporation of this eminent family of materials into data storage applications by fully arousing their intrinsic potential.",1301.5455v2 2014-04-17,Large Noncollinearity and Spin Reorientation in the Novel Mn2RhSn Heusler Magnet,"Noncollinear magnets provide essential ingredients for the next generation memory technology. It is a new prospect for the Heusler materials, already well known due to the diverse range of other fundamental characteristics. Here, we present a combined experimental and theoretical study of novel noncollinear tetragonal Mn2RhSn Heusler material exhibiting unusually strong canting of its magnetic sublattices. It undergoes a spin-reorientation transition, induced by a temperature change and suppressed by an external magnetic field. Because of the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn2RhSn is suggested to be a promising candidate for realizing the Skyrmion state in the Heusler family.",1404.4581v2 2014-05-06,Theoretical search for half-Heusler topological insulators,"We have performed ab-initio band structure calculations on more than two thousand half-Heusler compounds in order to search for new candidates for topological insulators. Herein, LiAuS and NaAuS are found to be the strongest topological insulators with the bulk band gap of 0.20 and 0.19 eV, respectively, different from the zero band gap feature reported in other Heusler topological insulators. Due to the inversion asymmetry of the Heusler structure, their topological surface states on the top and bottom surfaces exhibit p-type and n-type carriers, respectively. Thus, these materials may serve as an ideal platform for the realization of topological magneto-electric effects as polar topological insulators. Moreover, these topological surface states exhibit the right-hand spin-texture in the upper Dirac cone, which distinguish them from currently known topological insulator materials. Their topological nontrivial character remains robust against in-plane strains, which makes them suitable for epitaxial growth of films.",1405.1305v1 2014-12-01,Quality of Heusler Single Crystals Examined by Depth Dependent Positron Annihilation Techniques,"Heusler compounds exhibit a wide range of different electronic ground states and are hence expected to be applicable as functional materials in novel electronic and spintronic devices. Since the growth of large and defect-free Heusler crystals is still challenging, single crystals of Fe2TiSn and Cu2MnAl were grown by the optical floating zone technique. Two positron annihilation techniques -Angular Correlation of Annihilation Radiation (ACAR) and Doppler Broadening Spectroscopy (DBS)- were applied in order to study both, the electronic structure and lattice defects. Recently, we succeeded to observe clearly the anisotropy of the Fermi surface of Cu2MnAl, whereas the spectra of Fe2TiSn were disturbed by foreign phases. In order to estimate the defect concentration in different samples of Heusler compounds the positron diffusion length was determined by DBS using a monoenergetic positron beam.",1412.0435v1 2015-02-11,High thermoelectric figure of merit in p-type Half-Heuslers by intrinsic phase separation,"Improvements in the thermoelectric properties of Half-Heusler materials have been achieved by means of a micrometer-scale phase separation that increases the phonon scattering and reduces the lattice thermal conductivity. A detailed study of the p-type Half-Heusler compounds Ti(1-x)Hf(x)CoSb0.85Sn0.15 using high-resolution synchrotron powder X-ray diffraction and element mapping electron microscopy evidences the outstanding thermoelectric properties of this system. A combination of intrinsic phase separation and adjustment of the carrier concentration via Sn substitution is used to realize a record thermoelectric figure of merit for p-type Half-Heusler compounds of ZT around 1.15 at 710C in Ti0.25Hf0.75CoSb0.85Sn0.15. The phase separation approach can form a significant alternative to nanostructuring processing time, energy consumption and increasing the thermoelectric efficiency.",1502.03336v1 2015-06-04,Low-moment ferrimagnetic phase of the Heusler compound Cr2CoAl,"Synthesizing half-metallic fully-compensated ferrimagnets that form in the inverse Heusler phase could lead to superior spintronic devices. These materials would have high spin polarization at room temperature with very little fringing magnetic fields. Previous theoretical studies indicated that Cr2CoAl should form in a stable inverse Heusler lattice due to its low activation energy. Here, stoichiometric Cr2CoAl samples were arc-melted and annealed at varying temperatures, followed by studies of their structural and magnetic properties. High-resolution synchrotron X-ray diffraction revealed a chemically ordered Heusler phase in addition to CoAl and Cr phases. Soft X-ray magnetic circular dichroism revealed that the Cr and Co magnetic moments are antiferromagnetically oriented leading to the observed low magnetic moment in Cr2CoAl.",1506.01738v1 2016-02-18,"Observation of Unusual Topological Surface States in Half-Heusler Compounds LnPtBi (Ln=Lu, Y)","Topological quantum materials represent a new class of matter with both exotic physical phenomena and novel application potentials. Many Heusler compounds, which exhibit rich emergent properties such as unusual magnetism, superconductivity and heavy fermion behaviour, have been predicted to host non-trivial topological electronic structures. The coexistence of topological order and other unusual properties makes Heusler materials ideal platform to search for new topological quantum phases (such as quantum anomalous Hall insulator and topological superconductor). By carrying out angle-resolved photoemission spectroscopy (ARPES) and ab initio calculations on rare-earth half-Heusler compounds LnPtBi (Ln=Lu, Y), we directly observed the unusual topological surface states on these materials, establishing them as first members with non-trivial topological electronic structure in this class of materials. Moreover, as LnPtBi compounds are non-centrosymmetric superconductors, our discovery further highlights them as promising candidates of topological superconductors.",1602.05633v2 2020-01-06,Giant anomalous Hall and Nernst effect in magnetic cubic Heusler compounds,"The interplay of magnetism and topology opens up the possibility for exotic linear response effects, such as the anomalous Hall effect and the anomalous Nernst effect, which can be strongly enhanced by designing a strong Berry curvature in the electronic structure. It is even possible to utilize this to create a quantum anomalous Hall state at high temperatures by reducing the dimensionality. Magnetic Heusler compounds are a promising class of materials for this purpose because they grow in thin films, have a high Curie temperature, and their electronic structure hosts strong topological features. Here, we provide a comprehensive study of the intrinsic anomalous transport for magnetic cubic full Heusler compounds and we illustrate that several Heusler compounds outperform the best so far reported materials. The results reveal the importance of symmetries, especially mirror planes, in combination with magnetism for giant anomalous Hall and Nernst effects, which should be valid in general for linear responses (spin Hall effect, spin orbital torque, etc.) dominated by intrinsic contributions.",2001.01698v3 2017-04-06,A critical study of the elastic properties and stability of Heusler compounds: Phase change and tetragonal $X_{2}YZ$ compounds,"In the present work, the elastic constants and derived properties of tetragonal and cubic Heusler compounds were calculated using the high accuracy of the full-potential linearized augmented plane wave (FPLAPW). To find the criteria required for an accurate calculation, the consequences of increasing the numbers of $k$-points and plane waves on the convergence of the calculated elastic constants were explored. Once accurate elastic constants were calculated, elastic anisotropies, sound velocities, Debye temperatures, malleability, and other measurable physical properties were determined for the studied systems. The elastic properties suggested metallic bonding with intermediate malleability, between brittle and ductile, for the studied Heusler compounds. To address the effect of off-stoichiometry on the mechanical properties, the virtual crystal approximation (VCA) was used to calculate the elastic constants. The results indicated that an extreme correlation exists between the anisotropy ratio and the stoichiometry of the Heusler compounds, especially in the case of Ni$_{2}$MnGa.",1704.01741v1 2018-08-14,Screening potential topological insulators in half-Heusler compounds via compressed-sensing,"Ternary half-Heusler compounds with widely tunable electronic structures, present a new platform to discover topological insulators. Due to time-consuming computations and synthesis procedures, the identification of new topological insulators is however a rough task. Here, we adopt a compressed-sensing approach to rapidly screen potential topological insulators in half-Heusler family, which is realized via a two-dimensional descriptor that only depends on the fundamental properties of the constituent atoms. Beyond the finite training data, the proposed descriptor is employed to screen many new half-Heusler compounds, including those with integer and fractional stoichiometry, and a larger number of possible topological insulators are predicted.",1808.04748v5 2018-12-14,Formation of two-dimensional electron and hole gases at the interface of half-Heusler semiconductors,"Heuslers are a prominent family of multi-functional materials that includes semiconductors, half metals, topological semimetals, and magnetic superconductors. Owing to their same crystalline structure, yet quite different electronic properties and flexibility in chemical composition, Heusler-based heterostructures can be designed to show intriguing properties at the interface. Using electronic structure calculations, we show that two dimensional electron or hole gases (2DEG or 2DHG) form at the interface of half-Heusler (HH) semiconductors without any chemical doping. We use CoTiSb/NiTiSn as an example, and show that the 2DEG at the TiSb/Ni(001) termination and the 2DHG at the Co/TiSn(001) termination are intrinsic to the interface, and hold rather high charge densities of 3x10^14 carriers/cm^2. These excess charge carriers are tightly bound to the interface plane and are fully accommodated in transition-metal d sub-bands. The formation of 2DEG and 2DHG are not specific to the CoTiSb/NiTiSn system; a list of combinations of HH semiconductors that are predicted to form 2DEG or 2DHG is provided based on band alignment, interface termination, and lattice mismatch.",1812.05991v1 2017-10-03,Search for Thermoelectrics with High Figure of Merit in half-Heusler compounds with multinary substitution,"In order to improve the thermoelectric performance of TiCoSb we have substituted 50% of Ti equally with Zr and Hf at Ti site and Sb with Sn and Se equally at Sb site. The electronic structure of Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 is investigated using the full potential linearized augmented plane wave method and the thermoelectric transport properties are calculated on the basis of semi-classical Boltzmann transport theory. Our band structure calculations show that Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has semiconducting behavior with indirect band gap value of 0.98 eV which follow the empirical rule of 18 valence-electron content to bring semiconductivity in half Heusler compounds, indicating that one can have semiconducting behavior in multinary phase of half Heusler compounds if they full fill the 18 VEC rule and this open-up the possibility of designing thermoelectrics with high figure of merit in half Heusler compounds. We show that at high temperature of around 700K Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has high thermoelectric figure of merit of ZT = 1.05 which is higher than that of TiCoSb (~ 0.95) suggesting that by going from ternary to multinary phase system one can enhance the thermoelectric figure of merit at higher temperatures.",1710.01012v1 2021-02-03,First principles design of Ohmic spin diodes based on quaternary Heusler compounds,"The Ohmic spin diode (OSD) is a recent concept in spintronics, which is based on half-metallic magnets (HMMs) and spin-gapless semiconductors (SGSs). Quaternary Heusler compounds offer a unique platform to realize the OSD for room temperature applications as these materials possess very high Curie temperatures as well as half-metallic and spin-gapless semiconducting behavior within the same family. Using state-of-the-art first-principles calculations combined with the non-equilibrium Green's function method we design four different OSDs based on half-metallic and spin-gapless semiconducting quaternary Heusler compounds. All four OSDs exhibit linear current-voltage ($I-V$) characteristics with zero threshold voltage $V_T$. We show that these OSDs possess a small leakage current, which stems from the overlap of the conduction and valence band edges of opposite spin channels around the Fermi level in the SGS electrodes. The obtained on/off current ratios vary between $30$ and $10^5$. Our results can pave the way for the experimental fabrication of the OSDs within the family of ordered quaternary Heusler compounds.",2102.01919v1 2021-06-02,MgPd$_2$Sb -- the first Mg-based Heusler-type superconductor,"We report the synthesis and physical properties of a full Heusler compound, MgPd$_2$Sb, which we found to show superconductivity below $T_c$ = 2.2 K. MgPd$_2$Sb was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure (Fm-3m, a=6.4523(1) \r{A}) were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that MgPd$_2$Sb is a type-II, weak coupling superconductor ($\lambda_{e-p}$ = 0.53). The observed pressure dependence of $T_c$ ($\Delta T_c / p \approx $ -0.23 K/GPa) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in MgPd$_2$Sb were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters tothose of all reported Heusler-type superconductors.",2106.01133v2 2021-10-20,Anomalous Hall effect from gapped nodal line in Co2FeGe Heusler compound,"Full Heusler compounds with Cobalt as a primary element show anomalous transport properties owing to the Weyl fermions and broken time-reversal symmetry. We present here the study of anomalous Hall effect (AHE) in Co2FeGe Heusler compound. The experiment reveals anomalous Hall conductivity (AHC) 100 S/cm at room temperature with an intrinsic contribution of 78 S/cm . The analysis of anomalous Hall resistivity suggests the scattering independent intrinsic mechanism dominates the overall behaviour of anomalous Hall resistivity. The first principles calculation reveals that the Berry curvature originated by gapped nodal line near EF is the main source of AHE in Co2FeGe Heusler compound. The theoretically calculated AHC is in agreement with the experiment.",2110.10677v1 2005-09-18,Covalent bonding and the nature of band gaps in some half-Heusler compounds,"Half-Heusler compounds \textit{XYZ}, also called semi-Heusler compounds, crystallize in the MgAgAs structure, in the space group $F\bar43m$. We report a systematic examination of band gaps and the nature (covalent or ionic) of bonding in semiconducting 8- and 18- electron half-Heusler compounds through first-principles density functional calculations. We find the most appropriate description of these compounds from the viewpoint of electronic structures is one of a \textit{YZ} zinc blende lattice stuffed by the \textit{X} ion. Simple valence rules are obeyed for bonding in the 8-electron compound. For example, LiMgN can be written Li$^+$ + (MgN)$^-$, and (MgN)$^-$, which is isoelectronic with (SiSi), forms a zinc blende lattice. The 18-electron compounds can similarly be considered as obeying valence rules. A semiconductor such as TiCoSb can be written Ti$^{4+}$ + (CoSb)$^{4-}$; the latter unit is isoelectronic and isostructural with zinc-blende GaSb. For both the 8- and 18-electron compounds, when \textit{X} is fixed as some electropositive cation, the computed band gap varies approximately as the difference in Pauling electronegativities of \textit{Y} and \textit{Z}. What is particularly exciting is that this simple idea of a covalently bonded \textit{YZ} lattice can also be extended to the very important \textit{magnetic} half-Heusler phases; we describe these as valence compounds \textit{ie.} possessing a band gap at the Fermi energy albeit only in one spin direction. The \textit{local} moment in these magnetic compounds resides on the \textit{X} site.",0509472v1 2015-11-15,Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films,"The discovery of topological insulators (TIs), materials with bulk band gaps and protected cross-gap surface states, in compounds such as Bi2Se3 has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theory calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally-identical but electronically-varied nature of Heusler compounds. Here, we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin and angle-resolved photoemission spectroscopy (ARPES), complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of TI behavior is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronics devices.",1511.04778v3 2018-12-07,Systematic understanding of half-metallicity of ternary compounds in Heusler and Inverse Heusler structures with 3$d$ and 4$d$ elements,"Employing {\it ab initio} electronic structure calculations we extensively study ternary Heusler compounds having the chemical formula X$_2$X$^\prime$Z, where X = Mn, Fe or Co; Z = Al or Si; and X$^\prime$ changes along the row of 4$d$ transition metals. A comprehensive overview of these compounds, addressing the trends in structural, electronic, magnetic properties and Curie temperature is presented here along with the search for new materials for spintronics applications. A simple picture of hybridization of the $d$ orbitals of the neighboring atoms is used to explain the origin of the half-metallic gap in these compounds. We show that arrangements of the magnetic atoms in different Heusler lattices are largely responsible for the interatomic exchange interactions that are correlated with the features in their electronic structures as well as possibility of half-metallicity. We find seven half-metallic magnets with 100\% spin polarization. We identify few other compounds with high spin polarisation as ""near half-metals"" which could be of potential use in applications as well. We find that the major features in the electronic structures remain intact if a 3$d$ X$^{\prime}$ constituent is replaced with an isoelectronic 4$d$, implying that the total number of valence electrons can be used as a predictor of half-metallic nature in compounds from Heusler family.",1812.02856v1 2019-05-20,Band alignment and scattering considerations for enhancing the thermoelectric power factor of complex materials: The case of Co-based half-Heuslers,"Half-Heuslers, an emerging thermoelectric material group, has complex bandstructures with multiple bands that can be aligned through band engineering approaches, giving us an opportunity to improve their power factor. In this work, going beyond the constant relaxation time approximation, we perform an investigation of the benefits of band alignment in improving the thermoelectric power factor under different density of states dependent scattering scenarios. As a test case we consider the Co-based p-type half-Heuslers TiCoSb, NbCoSn and ZrCoSb. First, using simplified effective mass models combined with Boltzmann transport, we investigate the conditions of band alignment that are beneficial to the thermoelectric power factor under three different carrier scattering scenarios: i) the usual constant relaxation time approximation, ii) intra-band scattering restricted to the current valley with the scattering rates proportional to the density of states as dictated by Fermi's Golden Rule, and iii) both intra- and inter-band scattering across all available valleys, with the rates determined by the total density of states at the relevant energies. We demonstrate that the band-alignment outcome differs significantly depending on the scattering details. Next, using the density functional theory calculated bandstructures of the half-Heuslers we study their power factor behavior under strain induced band alignment. We show that strain can improve the power factor of half-Heuslers, but the outcome heavily depends on the curvatures of the bands involved, the specifics of the carrier scattering mechanisms, and the initial band separation. Importantly, we also demonstrate that band alignment is not always beneficial to the power factor.",1905.07951v1 2020-03-25,Tetragonal superstructure of the antiskyrmion hosting Heusler compound Mn1.4PtSn,"Skyrmions in non-centrosymmetric magnets are vortex-like spin arrangements, viewed as potential candidates for information storage devices. The crystal structure and non-collinear magnetic structure together with magnetic and spin-orbit interactions define the symmetry of the Skyrmion structure. We outline the importance of these parameters in the Heusler compound Mn1.4PtSn which hosts antiskyrmions, a vortex-like spin texture related to skyrmions.1 We overcome the challenge of growing large micro-twin-free single crystals of Mn1.4PtSn which has proved to be the bottleneck for realizing bulk skyrmionic/antiskyrmionic states in a compound. The use of 5d-transition metal, platinum, together with manganese as constituents in the Heusler compound such as Mn1.4PtSn is a precondition for the non-collinear magnetic structure. Due to the tetragonal inverse Heusler structure, Mn1.4PtSn exhibits large magneto-crystalline anisotropy and D2d symmetry, which are necessary for antiskyrmions. The superstructure in Mn1.4PtSn is induced by Mn-vacancies which enables a ferromagnetic exchange interaction to occur. Mn1.4PtSn, the first known tetragonal Heusler superstructure compound, opens up a new research direction for properties related to the superstructure in a family containing thousands of compounds.",2003.11344v1 2021-01-26,Co$_2$FeAl full Heusler compound based spintronic terahertz emitter,"To achieve a large terahertz (THz) amplitude from a spintronic THz emitter (STE), materials with 100\% spin polarisation such as Co-based Heusler compounds as the ferromagnetic layer are required. However, these compounds are known to loose their half-metallicity in the ultrathin film regime, as it is difficult to achieve L2$_1$ ordering, which has become a bottleneck for the film growth. Here, the successful deposition using room temperature DC sputtering of the L2$_1$ and B2 ordered phases of the Co$_2$FeAl full Heusler compound is reported. Co$_2$FeAl is used as ferromagnetic layer together with highly orientated Pt as non-ferromagnetic layer in the Co$_2$FeAl/Pt STE, where an MgO(10 nm) seed layer plays an important role to achieve the L2$_1$ and B2 ordering of Co$_2$FeAl. The generation of THz radiation in the CFA/Pt STE is presented, which has a bandwidth in the range of 0.1-4 THz. The THz electric field amplitude is optimized with respect to thickness, orientation, and growth parameters using a thickness dependent model considering the optically induced spin current, superdiffusive spin current, inverse spin Hall effect and the attenuation of THz radiation in the layers. This study, based on the full Heusler Co$_2$FeAl compound opens up a plethora possibilities in STE research involving full Heusler compounds.",2101.10911v1 2021-03-15,Design of Eutectic High Entropy Alloys,"Eutectic high entropy alloys (EHEAs) are emerging as an exciting new class of structural alloys as they have shown very promising mechanical properties. However, how to design these alloys has been a challenge. In this work, a simple approach is presented for designing EHEAs. The introduced approach uses the composition of binary and ternary eutectic alloys for finding the composition of EHEAs. The approach is based on the assumption that EHEAs are originated from binary and ternary eutectic alloys. The approach is applied for alloy systems Al-Co-Cr-Fe-Ni, Co-Cr-Fe-Ni, Co-Cr-Fe-Ni-Ti, and Co-Cr-Fe-Ni-Ta and several EHEAs are predicted for these alloy systems. The predicted results are verified with thermodynamic simulations and experimental data. The results show that the introduced approach can be considered as a feasible and easy-to-use method for designing EHEAs. Based on the developed approach, any binary eutectic alloy can be used for designing multicomponent eutectic alloys.",2103.08216v2 2019-03-19,Composition dependence of magnetoresistance in Fe$_{1-x}$Ni$_{x}$ alloys,"Resistance of Fe$_{1-x}$Ni$_x$(x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.9) has been measured using four probe method from 5K to 300K with and without a longitudinal magnetic field of 8T. The zero field resistivity of x=0.1 and 0.9 alloys, predominant contribution to resistivity above near room temperature is due to electron-phonon scattering, whereas for x=05 and 0.7 alloys electron-magnon scattering is dominant. Alloys with x=0.1 and 0.9 exhibit positive magnetoresistance(MR) from 5K to 300K. For x=0.5 and 0.7 alloys, magnetoresistance changes sign from positive to negative with increase in temperature. The temperature at which sign changes increase with Ni concentration in the alloy. The field dependent magnetoresistance is positive for x=0.1, 0.7 and 0.9 alloys whereas it is negative for x=0.5 alloy. MR follows linear behaviour with field for x=0.1 alloy. MR of all other alloys follow a second order polynomial in field.",1903.08230v3 2020-10-06,Short-range order in GeSn alloy,"Group IV alloys have been long viewed as homogeneous random solid solutions since they were first perceived as Si-compatible, direct-band-gap semiconductors 30 years ago. Such a perception underlies the understanding, interpretation and prediction of alloys' properties. However, as the race to create scalable and tunable device materials enters a composition domain far beyond alloys' equilibrium solubility, a fundamental question emerges as to how random these alloys truly are. Here we show, by combining statistical sampling and large-scale ab initio calculations, that GeSn alloy, a promising group IV alloy for mid-infrared technology, exhibits a clear, short-range order for solute atoms within its entire composition range. Such short-range order is further found to substantially affect the electronic properties of GeSn. We demonstrate the proper inclusion of this short-range order through canonical sampling can lead to a significant improvement over previous predictions on alloy's band gaps, by showing an excellent agreement with experiments within the entire studied composition range. Our finding thus not only calls for an important revision of current structural model for group IV alloy, but also suggests short-range order may generically exist in different types of alloys.",2010.02991v2 2021-08-25,Predictive model of surface adsorption in dissolution on transition metals and alloys,"Surface adsorption, which is often coupled with surface dissolution, is generally unpredictable on alloys due to the complicated alloying and dissolution effects. Herein, we introduce the electronic gradient and cohesive properties of surface sites to characterize the effects of alloying and dissolution. This enables us to build a predictive model for the quantitative determination of the adsorption energy in dissolution, which holds well for transition metals, near-surface alloys, binary alloys, and high-entropy alloys. Furthermore, this model uncovers a synergistic mechanism between the d-band upper-edge ratio, d-band width and s-band depth in determining the alloying and dissolution effects on adsorption. Our study not only provides fundamental mechanistic insights into surface adsorption on alloys but also offers a long-sought tool for the design of advanced alloy catalysts.",2108.11017v1 2021-09-21,Sustainable low-cost method for production of High entropy alloys from alloy scraps,"In this communication,we propose a sustainable way to produce high entropy alloys from alloy scraps called Alloy mixing.We successfully demonstrate this method using a near equimolar CrCuFeMnNi HEA. Alloy scraps (304L stainless steel, Nichrome 80 and electrical wire grade Copper) obtained from various sources were melted together using vacuum arc melting along with minor additions of Mn and Cr to achieve the equiatomic composition.The alloy was characterized using X-ray Diffraction (XRD) and Scanning Electron Microscopy, which confirmed that the alloy produced through Alloy mixing exhibits a microstructure similar to that of the alloy with the same composition produced through conventional melting of pure elements",2109.10276v2 2024-01-15,High entropy alloys and their affinity to hydrogen: from Cantor to platinum group elements alloys,"Properties of high entropy alloys are currently in the spotlight due to their promising applications. One of the least investigated aspects is the affinity of these alloys to hydrogen, its diffusion and reactions. In this study we apply high-pressure at ambient temperature and investigate stress-induced diffusion of hydrogen into the tructure of high entropy alloys HEA including the famous Cantor alloy as well as less known, but nevertheless important platinum group PGM alloys. By applying X-ray diffraction to samples loaded into diamond anvil cells we perform a comparative investigation of these HEA alloys in Ne and H2 pressure-transmitting media. Surprisingly, even under stresses far exceeding conventional industrial processes both Cantor and PGM alloys show exceptional resistance to hydride formation, on par with widely used industrial grade CuBe alloys. Our observations inspire optimism for practical HEA applications in hydrogen-relevant industry and technology e.g. coatings, etc, particularly those related to transport and storage.",2401.07802v1 2018-08-09,Underlying burning resistant mechanisms for titanium alloy,"The ""titanium fire"" as produced during high pressure and friction is the major failure scenario for aero-engines. To alleviate this issue, Ti-V-Cr and Ti-Cu-Al series burn resistant titanium alloys have been developed. However, which burn resistant alloy exhibit better property with reasonable cost needs to be evaluated. This work unveils the burning mechanisms of these alloys and discusses whether burn resistance of Cr and V can be replaced by Cu, on which thorough exploration is lacking. Two representative burn resistant alloys are considered, including Ti14(Ti-13Cu-1Al-0.2Si) and Ti40(Ti-25V-15Cr-0.2Si)alloys. Compared with the commercial non-burn resistant titanium alloy, i.e., TC4(Ti-6Al-4V)alloy, it has been found that both Ti14 and Ti40 alloys form ""protective"" shields during the burning process. Specifically, for Ti14 alloy, a clear Cu-rich layer is formed at the interface between burning product zone and heat affected zone, which consumes oxygen by producing Cu-O compounds and impedes the reaction with Ti-matrix. This work has established a fundamental understanding of burning resistant mechanisms for titanium alloys. Importantly, it is found that Cu could endow titanium alloys with similar burn resistant capability as that of V or Cr, which opens a cost-effective avenue to design burn resistant titanium alloys.",1808.02976v1 2020-03-23,Plasma Surface Metallurgy of Materials Based on Double Glow Discharge Phenomenon,"Plasma Surface Metallurgy/Alloying is a kind of surface metallurgy/alloying to employ low temperature plasma produced by glow discharge to diffuse alloying elements into the surface of substrate material to form an alloy layer. The first plasma surface metallurgy technology is plasma nitriding invented by German scientist Dr. Bernard Berghuas in 1930. He was the first person to apply glow discharge to realize the surface alloying. In order to break the limitation of plasma nitriding technology, which can only be applied to a few non-metallic gaseous elements such as nitrogen, carbon, sulfur, the ""Double Glow Discharge Phenomenon""was found in 1978. Based on this phenomenon the ""Double Glow Plasma Surface Metallurgy Technology"", also known as the ""Xu-Tec Process"" was invented in 1980. It can utilize any chemical elements in the periodic table including solid metallic, gas non-metallic elements and their combination to realize plasma surface alloying, hence greatly expanded the field of surface alloying. Countless surface alloys with high hardness, wear resistance and corrosion resistance, such as high speed steels, nickel base alloys and burn resistant alloys have been produced on the surfaces of a variety of materials. This technology may greatly improve the surface properties of metal materials, comprehensively improve the quality of mechanical products, save a lot of precious alloy elements for human beings. Based on the plasma nitriding technology, the Xu-Tec Process has opened up a new material engineering field of ""Plasma Surface Metallurgy"". This Review Article briefly presents the history of glow discharge and surface alloying, double glow discharge phenomenon, basic principle and current status of Double Glow Plasma Surface Metallurgy/Alloying. Industrial applications, advantages and future potential of the Xu-Tec process are also presented.",2003.10250v1 2014-08-01,Hexagonal High-Entropy Alloys,"We report on the discovery of a high-entropy alloy with a hexagonal crystal structure. Equiatomic samples in the alloy system Ho-Dy-Y-Gd-Tb were found to solidify as homogeneous single-phase high-entropy alloys. The results of our electron diffraction investigations and high-resolution scanning transmission electron microscopy are consistent with a Mg-type hexagonal structure. The possibility of hexagonal high-entropy alloys in other alloy systems is discussed.",1408.0100v3 2016-01-03,Depletion Gilding: An Ancient Method for Surface Enrichment of Gold Alloys,"Ancient objects made of noble metal alloys, that is, gold with copper and/or silver, can show the phenomenon of surface enrichment. This phenomenon is regarding the composition of the surface, which has a percentage of gold higher than that of the bulk. This enrichment is obtained by a depletion of the other elements of the alloy, which are, in some manner, removed. This depletion gilding process was used by pre-Columbian populations for their 'tumbaga', a gold-copper alloy, to give it the luster of gold.",1601.00845v1 2017-07-26,Molecular dynamics study of plasticity in Al-Cu alloy nanopillar due to compressive loading,"In this paper, compressive loading effects on the plasticity of Al-Cu alloy varying the crystal orientation of Al and alloying element (Cu) percentage are investigated using molecular dynamics approach. The alloying percentage of Cu are varied up to 10% in <001>, <110> and <111> crystal loading direction of Al. Our results indicate that the alloy nanopillar has highest first yielding strength and strain along <110> and <001> direction, respectively. Further, the dislocation density and dislocation interaction are studied to explain the compressive stress strain behavior of the alloy nanopillar.",1707.08404v2 2019-08-07,DFT-based energy shifts screening of Na$_x$K$_{55-x}$ alloy clusters,"Compositional effects in NaK alloy clusters have been studied using bond order length strength notation and density functional theory calculations. The results reveal binding energy shifts of the NaK alloy clusters under different elemental compositions. Atomic arrangements that can be used to predict the structures of stable experimental NaK alloys were also obtained. Our study of these alloy nanoclusters has uncovered a trend correlating atomic position and composition with binding energy. We believe this data will help in the experimental preparation of alloy nanoclusters.",1908.02421v1 2019-09-01,"Low activation, refractory, high entropy alloys for nuclear applications","Two new, low activation high entropy alloys (HEAs) TiVZrTa and TiVCrTa are studied for use as in-core, structural nuclear materials for in-core nuclear applications. Low-activation is a desirable property for nuclear reactors, in an attempt to reduce the amount of high level radioactive waste upon decommissioning, and for consideration in fusion applications.The alloy TiVNbTa is used as a starting composition to develop two new HEAs; TiVZrTa and TiVCrTa. The new alloys exhibit comparable indentation hardness and modulus, to the TiVNbTa alloy in the as-cast state. After heavy ion implantation the new alloys show an increased irradiation resistance.",1909.00373v1 2018-08-01,Thick amorphous complexion formation and extreme thermal stability in ternary nanocrystalline Cu-Zr-Hf alloys,"Building on the recent discovery of tough nanocrystalline Cu-Zr alloys with amorphous intergranular films, this paper investigates ternary nanocrystalline Cu-Zr-Hf alloys with a focus on understanding how alloy composition affects the formation of disordered complexions. Binary Cu-Zr and Cu-Hf alloys with similar initial grain sizes were also fabricated for comparison. The thermal stability of the nanocrystalline alloys was evaluated by annealing at 950 {\deg}C (>95% of the solidus temperatures), followed by detailed characterization of the grain boundary structure. All of the ternary alloys exhibited exceptional thermal stability comparable to that of the binary Cu-Zr alloy, and remained nanocrystalline even after two weeks of annealing at this extremely high temperature. Despite carbide formation and growth in these alloys during milling and annealing, the thermal stability of the ternary alloys is mainly attributed to the formation of thick amorphous intergranular films at high temperatures. Our results show that ternary alloy compositions have thicker boundary films compared to the binary alloys with similar global dopant concentrations. While it is not required for amorphous complexion formation, this work shows that having at least three elements present at the interface can lead to thicker grain boundary films, which is expected to maximize the previously reported toughening effect.",1808.00507v5 2023-05-20,Mechanical Property Design of Bio-compatible Mg alloys using Machine-Learning Algorithms,"Magnesium alloys are attractive options for temporary bio-implants because of their biocompatibility, controlled corrosion rate, and similarity to natural bone in terms of stiffness and density. Nevertheless, their low mechanical strength hinders their use as cardiovascular stents and bone substitutes. While it is possible to engineer alloys with the desired mechanical strength, optimizing the mechanical properties of biocompatible magnesium alloys using conventional experimental methods is time-consuming and expensive. Therefore, Artificial Intelligence (AI) can be leveraged to streamline the alloy design process and reduce the required time. In this study, a machine learning model was developed to predict the yield strength (YS) of biocompatible magnesium alloys with an $R^2$ accuracy of 91\%. The predictive model was then validated using the CALPHAD technique and thermodynamics calculations. Next, the predictive model was employed as the fitness function of a genetic algorithm to optimize the alloy composition for high-strength biocompatible magnesium implants. As a result, two alloys were proposed and synthesized, exhibiting YS values of 108 and 113 MPa, respectively. These values were substantially higher than those of conventional magnesium biocompatible alloys and closer to the YS and compressive strength of natural bone. Finally, the synthesized alloys were subjected to microstructure analysis and mechanical property testing to validate and evaluate the performance of the proposed AI-based alloy design approach for creating alloys with specific properties suitable for diverse applications.",2305.12060v1 2008-11-02,Ab-initio simulation and experimental validation of beta-titanium alloys,"In this progress report we present a new approach to the ab-initio guided bottom up design of beta-Ti alloys for biomedical applications using a quantum mechanical simulation method in conjunction with experiments. Parameter-free density functional theory calculations are used to provide theoretical guidance in selecting and optimizing Ti-based alloys with respect to three constraints: (i) the use of non-toxic alloy elements; (ii) the stabilization of the body centered cubic beta phase at room temperature; (iii) the reduction of the elastic stiffness compared to existing Ti-based alloys. Following the theoretical predictions, the alloys of interest are cast and characterized with respect to their crystallographic structure, microstructure, texture, and elastic stiffness. Due to the complexity of the ab initio calculations, the simulations have been focused on a set of binary systems of Ti with two different high melting bcc metals, namely, Nb and Mo. Various levels of model approximations to describe mechanical and thermodynamic properties are tested and critically evaluated. The experiments are conducted both, on some of the binary alloys and on two more complex engineering alloy variants, namely, Ti-35wt.%Nb-7wt.%Zr-5wt.%Ta and a Ti-20wt.%Mo-7wt.%Zr-5wt.%Ta.",0811.0157v1 2009-03-13,Half-metallic ferrimagnetism in the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x} $V$_x$]Si alloys adopting the zinc-blende and wurtzite structures from first-principles,"Employing first-principles calculations we study the structural, electronic and magnetic properties of the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x}$V$_x$]Si alloys. In their equilibrium rocksalt structure all alloys are non-magnetic. The zincblende and wurtzite structures are degenerated with respect to the total energy. For all concentrations the alloys in these lattice structures are half-metallic with the gap located in the spin-down band. The total spin moment follows the Slater-Pauling behavior varying linearly between the -1 $\mu_B$ of the perfect ScC and ScSi alloys and the +1 $\mu_B$ of the perfect VC and VSi alloys. For the intermediate concentrations V and Sc atoms have antiparallel spin magnetic moments and the compounds are half-metallic ferrimagnets. At the critical concentration, both [Sc$_{0.5}$V$_{0.5}$]C and [Sc$_{0.5}$V$_{0.5}$]Si alloys present zero total spin-magnetic moment but the C-based alloy shows a semiconducting behavior contrary to the Si-based alloys which is a half-metallic antiferromagnet.",0903.2331v1 2009-05-07,Research of Mechanical Properties of Ni-Ti-Nb Alloyson Low Temperature and Restriction Behavior,"Mechanical Properties of Ni-Ti-Nb alloys with these conditions of cold-drawing, non-vacuum heat treatment and vacuum heat treatment were measured at low temperature, and Mechanical Properties of Ni47Ti44Nb9 alloys of restricting recover was compared with the one of alloys of non-restricting recover, and these rules of the mechanical performance between them was analyzed. Experiment indicates that, mechanical Properties of vacuum heat treatment's alloys was more excellent than the other two (non-vacuum heat treatment and cold-drawing), and the stress curves of alloys of restricting recover haven't the evident yield band, and the stress of alloys of restricting recover was higher than the ones of alloys of non-restricting recover, but the stress of alloys of restricting recover was lower than the ones of alloys of non-restricting recover.",0905.0967v2 2012-05-07,Gamma-irradiation influence on the initial magnetic conductivity of based on the system Fe-Si-B amorphous and nanocrystalline alloys,"The dependence of initial magnetic permeability {\mu}i of based on the Fe-Si-B amorphous and nanocrystalline alloys on the {\gamma}-irradiation dose was investigated by the method of inductance factor determination. It was determined that the alloying of amorphous Fe-Si-B alloys by nickel and molybdenum increases the radiation sensitivity of the {\mu}i. Initial magnetic permeability of nanocrystalline magnetic alloys is less sensitive to the action of {\gamma}-irradiation as compared with the alloyed amorphous alloys. Has been suggested that radiation influence on the initial magnetic permeability are caused by creation of non-magnetic incorporation in structure of amorphous alloys as well as amorphous matrix of nanocrystalline alloys.",1205.1354v1 2013-07-15,Characterization of Al and Mg Alloys from Their X-Ray Emission Bands,"The valence states of Mg-Al alloys are compared to those of reference materials (pure Mg and Al metals, and intermetallics). Two methods based on X-ray emission spectroscopy are proposed to determine the phases and their proportion: first, by analyzing the Al valence spectra of the Mg-rich alloys and the Mg valence spectra of the Al-rich alloys; second, by fitting with a linear combination of the reference spectra the Al spectra of the Al-rich alloys and the Mg spectra of the Mg-rich alloys. This enables us to determine that Al and Al3Mg2 are present in the 0-43.9 wt% Al composition range and Mg and Al12Mg17 are present in the 62.5-100 wt% Al composition range. In the 43.9-62.5% Al range, the alloy is single phase and an underestimation of the Al content of the alloy can be estimated from the comparison of the bandwidth of the alloy spectrum to the bandwidths of the reference spectra.",1307.3959v1 2013-11-06,Characterization of poly- and single-crystal uranium-molybdenum alloy thin films,"Poly- and single-crystal thin films of U-Mo alloys have been grown both on glass and sapphire substrates by UHV magnetron sputtering. X-ray and Electron Backscatter Diffraction data indicate that for single-crystal U1-xMox alloys, the pure cubic uranium gamma-phase exists for x > 0.22 (10 wt.% Mo). Below 10 wt.% Mo concentration, the resulting thin film alloys exhibited a mixed alpha-gamma uranium phase composition.",1311.1430v1 2020-01-22,The design of eutectic high entropy alloys in Al-Co-Cr-Fe-Ni system,"In the present work, a simple approach is proposed for predicting the compositions of eutectic high entropy alloys (EHEAs) in Al-Co-Cr-Fe-Ni system. It is proposed that eutectic lines exist between certain eutectic alloys in this system and, as a result, new eutectic or near-eutectic compositions can be obtained by mixing the alloys which are located on the same eutectic line. The approach is applied for a series of experimentally verified eutectic alloys and new eutectic or near-eutectic alloys are designed for Al-Co-Cr-Fe-Ni system. Furthermore, by investigating the compositions of verified eutectic alloys in Al-Co-Cr-Fe-Ni system, compositional diagrams are proposed which show the relations between the concentrations of constituent elements in eutectic alloys. The compositional diagrams suggest that EHEAs are derived from binary and ternary eutectic alloys. Moreover, the proposed diagrams can be considered as convenient methods for evaluating the composition of EHEAs in Al-Co-Cr-Fe-Ni system.",2001.07954v1 2021-07-06,A Transferable Machine-learning Scheme from Pure Metals to Alloys in Predicting Adsorption Energies,"Alloys present the great potential in catalysis because of their adjustable compositions, structures and element distributions, which unfortunately also limit the fast screening of the potential alloy catalysts. Machine learning methods are able to tackle the multi-variable issues but still cannot yet predict the complex alloy catalysts from the properties of pure metals due to the lack of universal descriptors. Herein we propose a transferable machine-learning model based on the intrinsic properties of substrates and adsorbates, which can predict the adsorption energies of single-atom alloys (SAAs), AB intermetallics (ABs) and high-entropy alloys (HEAs), simply by training the properties of transition metals (TMs). Furthermore, this model builds the structure-activity relationship of the adsorption energies on alloys from the perspective of machine learning, which reveals the role of the surface atoms' valence, electronegativity and coordination and the adsorbates' valence in determining the adsorption energies. This transferable scheme advances the understanding of the adsorption mechanism on alloys and the rapid design of alloy catalysts.",2107.02599v1 2019-01-06,Effect of copper content on thermal and mechanical properties of eutectoid zn-al alloy,"Zn-Al alloys have become one of the major engineering alloys among commercially available alloys. This study was conducted on eutectoid composition of Zn-Al alloy with an observation of the effect of copper addition. For this purpose, one eutectoid (Zn-22wt%Al) and three other alloys, adding 1wt%, 3wt% and 5wt% copper with this eutectoid composition, were molded in permanent metal mould. Microscopic studies exhibited varied grains which confirmed the formation of different phases. Moreover, the formation of different phases in micro study was supported by XRD analysis. Hardness of the samples were tested on Rockwell B scale and it was observed that the hardness of these alloys was substantially increased with the addition of copper. With increasing amount of copper, phase changing temperature of the alloys reveals a growing trend, which was observed by DTA analysis. From this study it was concluded that addition of copper can significantly add to the mechanical properties of Zn-Al alloys.",1901.01519v2 2019-08-13,Investigating the real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS,"The real-time dissolution of the single-phase compositionally complex alloy (CCA), Al1.5TiVCr, was studied using an inline inductively coupled plasma method. Compositionally complex alloys (CCAs), a term encompassing high entropy alloys (HEAs) or multi-principal element alloys (MPEAs), are - in general - noted for their inherently high corrosion resistance. In order to gain an insight into the dissolution of Al1.5TiVCr alloy, atomic emission spectroelectrochemistry was utilised in order to measure the ion dissolution of the alloy during anodic polarisation. It was revealed that incongruent dissolution occurred, with preferential dissolution of Al, and essentially no dissolution of Ti, until the point of alloy breakdown. Results were correlated with X-ray photoelectron spectroscopy, which revealed a complex surface oxide inclusive of unoxidised metal, and metal oxides in disproportion to the bulk alloying element ratio.",1908.04493v1 2020-11-14,The influence of alloying on the stacking fault energy of gold from density functional theory calculations,"The generalized stacking fault (SFE) energy curves of pure gold (Au) and its binary alloys with transition metals are determined from density functional theory (DFT). Alloy elements Ag, Al, Cu, Ni, Ti, Zr, Zn, In, Ga, Sn, Mn, Cd, Sn, Ta and Cr are substituted into Au at concentrations up to 4%. A comparison of various proposed methodologies to calculate SFEs is given. The intrinsic SFE decreases for all alloying elements from its value for pure Au, but SFE energies (both stable and unstable) vary strongly with the distance of the alloying element from the stacking fault region, and with alloy concentration. The compositional dependence of the SFE on the volume change associated with alloying element is determined. This work demonstrates that the SFE is strongly influenced by misfit strain caused by the alloying elements. Moreover, the computed generalized SFE curves provide information valuable to developing an understanding of the deformation behavior of Au and Au-alloys.",2011.07305v1 2021-01-07,Highly Distorted Lattices in Chemically Complex Alloys Produce Ultra-Elastic Materials with Extraordinary Elinvar Effects,"Conventional crystalline alloys usually possess a low atomic size difference in order to stabilize its crystalline structure. However, in this article, we report a single phase chemically complex alloy which possesses a large atomic size misfit usually unaffordable to conventional alloys. Consequently, this alloy develops a rather complex atomic-scale chemical order and a highly distorted crystalline structure. As a result, this crystalline alloy displays an unusually high elastic strain limit (~2%), about ten times of that of conventional alloys, and an extremely low internal friction (< 2E-4) at room temperature. More interestingly, this alloy firmly maintains its elastic modulus even when the testing temperature rises from room temperature to 900 K, which is unmatched by the existing alloys hitherto reported. From an application viewpoint, our discovery may open up new opportunities to design high precision devices usable even under an extreme environment.",2101.02382v1 2021-04-20,Accelerated Discovery of Molten Salt Corrosion-resistant Alloy by High-throughput Experimental and Modeling Methods Coupled to Data Analytics,"Insufficient availability of molten salt corrosion-resistant alloys severely limits the fruition of a variety of promising molten salt technologies that could otherwise have significant societal impacts. To accelerate alloy development for molten salt applications and develop fundamental understanding of corrosion in these environments, here we present an integrated approach using a set of high-throughput alloy synthesis, corrosion testing, and modeling coupled with automated characterization and machine learning. By using this approach, a broad range of Cr-Fe-Mn-Ni alloys were evaluated for their corrosion resistances in molten salt simultaneously demonstrating that corrosion-resistant alloy development can be accelerated by thousands of times. Based on the obtained results, we unveiled a sacrificial mechanism in the corrosion of Cr-Fe-Mn-Ni alloys in molten salts which can be applied to protect the less unstable elements in the alloy from being depleted, and provided new insights on the design of high-temperature molten salt corrosion-resistant alloys.",2104.10235v1 2021-08-13,Insight into Ideal Shear Strength of Ni-based Dilute Alloys using First-Principles Calculations and Correlational Analysis,"The present work examines the effect of alloying elements (denoted X) on the ideal shear strength for 26 dilute Ni-based alloys, Ni$_{11}$X, as determined by first-principles calculations of pure alias shear deformations. The variations in ideal shear strength are quantitatively explored with correlational analysis techniques, showing the importance of atomic properties such as size and electronegativity. The shear moduli of the alloys are affirmed to show a strong linear relationship with their ideal shear strengths, while the shear moduli of the individual alloying elements were not indicative of alloy shear strength. Through combination with available ideal shear strength data on Mg alloys, a potential application of the Ni alloy data is demonstrated in the search for a set of atomic features suitable for machine learning applications to mechanical properties. As another illustration, the predicted Ni ideal shear strengths play a key role in a predictive multiscale framework for deformation behavior of single crystal alloys at large strains, as shown by simulated stress-strain curves.",2108.06412v2 2021-10-18,Equilibrium Phase Diagrams of Isostructural and Heterostructural Two-Dimensional Alloys from First Principles,"Alloying is a successful strategy for tuning the phases and properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs). To accelerate the synthesis of new TMDC alloys, we present a method for generating temperature-composition equilibrium phase diagrams by combining first-principles total energy calculations with thermodynamic solution models. This method is applied to three representative 2D TMDC alloys: an isostructural alloy, MoS2(1-x)Te2x, and two heterostructural alloys, Mo1-xWxTe2 and WS2(1-x)Te2x. We show that the mixing enthalpy of the entire composition range of these binary alloys can be reliably represented using a sub-regular solution model fitted to the total energy of a small number of compositions that are calculated using density-functional theory on special quasi-random structures. The sub-regular solution model uses a cubic fit that captures three-body effects that are important in these TMDC alloys having hexagonal structures. By comparing both isostructural and heterostructural phase diagrams generated with this method to those calculated with cluster expansion methods, we demonstrate that this method can be used to rapidly design phase diagrams of TMDC alloys, and related 2D materials.",2110.09589v2 2023-09-09,High-throughput screening of coherent topologically close-packed precipitates in hexagonal close-packed metallic systems,"The nanoscale, coherent topologically close-packed (TCP) precipitate plates in magnesium alloys are found beneficial to the strength and creep resistance of alloys. However, the conventional trial-and-error method is too time-consuming and costly, which impedes the application of TCP precipitates to hcp-based metallic alloys. Here, we systematically screen the potential coherent TCP precipitate plates in the three most common hcp alloys, magnesium (Mg), titanium (Ti), and zirconium (Zr) alloys, using an efficient high-throughput screening methodology. Our findings indicate that the hcp-to-TCP structural transformations readily occur in Mg alloys, leading to abundant precipitation of TCP plates. However, hcp-Ti and Zr alloys exhibit a preference for hcp-to-bcc structural transformations, rather than the in situ precipitation of TCP plates. These screening results are largely consistent with experimental observations. The insights gained contribute to a deeper understanding of precipitation behavior in various hcp-based alloys at the atomic level and provide insightful reference results for designing novel alloys containing TCP phases.",2309.04822v2 2006-05-29,Epitaxy of thin films of the Heusler compound Co2Cr0.6Fe0.4Al,"Epitaxial thin films of the highly spin polarized Heusler compound Co2Cr0.6Fe0.4Al are deposited by dc magnetron sputtering. It is shown by XRD and TEM investigations how the use of an Fe buffer layer on MgO(100) substrates supports the growth of highly ordered Co2Cr0.6Fe0.4Al at low deposition temperatures. The as grown samples show a relatively large ordered magnetic moment of mu = 3.0mu_B/f.u. providing evidence for a low level of disorder.",0605698v2 2006-09-02,A new diluted magnetic semiconductor: The half-metallic ferromagnet CoTi(1-x)FexSb,"Half-Heusler compounds with 18 valence electrons are semi-conducting. It will be shown that doping with electrons results in half-metallic ferromagnets, similar to the case of diluted semi-conductors. CoTiSb is known to be a semi-conducting Half-Heusler compound. Doping by Fe is expected to result in ferromagnetic order. It was found that Ti can be replaced by up to about 10% Fe while its crystal structure still remains C1b, which was proved by X-ray powder diffraction. SQUID magnetometry revealed a magnetic moment of 0.32 mB per unit cell at 5K.",0609042v1 2006-10-17,Surface and bulk properties of the Heusler compound Co2Cr0.6Fe0.4Al: a Moessbauer study,"To explore its structural and magnetic properties, the Heusler compound Co2Cr0.6Fe0.4Al was investigated using Moessbauer spectroscopy. The results of both transmission and conversion electron Moessbauer spectroscopy (CEMS) are analyzed to obtain insight into both the disorder effects as well as the differences between bulk and surface properties. It was found that mechanical treatment of the surfaces of bulk samples causes disorder and phase segregation, effects that should be taken into consideration when performing studies using surface-informative techniques. Results from bulk sample CEMS measurements of Co2Cr0.6Fe0.4Al are used to interpret the thin film Moessbauer spectra of this compound.",0610480v1 2007-03-28,Crystalline electric fields and the magnetic ground state of the novel Heusler intermetallic YbRh$_{2}$Pb,"We have synthesized a new intermetallic compound with a distorted Heusler structure, YbRh$_{2}$Pb. We present a study of the magnetic, thermal, and transport properties. Heat capacity measurements revealed that YbRh$_{2}$Pb orders magnetically below T$_{N}$=0.57 K from a paramagnetic state with substantial crystal electric field splitting. Magnetic field further splits the ground state, which leads to the suppression of magnetic order in YbRh$_{2}$Pb.",0703765v2 1995-03-28,THE UNIQUENESS THEOREM FOR ROTATING BLACK HOLE SOLUTIONS OF SELF-GRAVITATING HARMONIC MAPPINGS,"We consider rotating black hole configurations of self-gravitating maps from spacetime into arbitrary Riemannian manifolds. We first establish the integrability conditions for the Killing fields generating the stationary and the axisymmetric isometry (circularity theorem). Restricting ourselves to mappings with harmonic action, we subsequently prove that the only stationary and axisymmetric, asymptotically flat black hole solution with regular event horizon is the Kerr metric. Together with the uniqueness result for non-rotating configurations and the strong rigidity theorem, this establishes the uniqueness of the Kerr family amongst all stationary black hole solutions of self-gravitating harmonic mappings.",9503053v1 1995-06-15,Pulsation of Spherically Symmetric Systems in General Relativity,"The pulsation equations for spherically symmetric black hole and soliton solutions are brought into a standard form. The formulae apply to a large class of field theoretical matter models and can easily be worked out for specific examples. The close relation to the energy principle in terms of the second variation of the Schwarzschild mass is also established. The use of the general expressions is illustrated for the Einstein-Yang-Mills and the Einstein-Skyrme system.",9506027v1 1996-10-11,No-Hair Theorems and Black Holes with Hair,"The critical steps leading to the uniqueness theorem for the Kerr-Newman metric are reexamined in the light of the new black hole solutions with Yang-Mills and scalar hair. Various methods -- including scaling techniques, arguments based on energy conditions, conformal transformations and divergence identities -- are reviewed, and their range of application to selfgravitating scalar and non-Abelian gauge fields is discussed. In particular, the no-hair theorem is extended to harmonic mappings with arbitrary Riemannian target manifolds. (This paper is an extended version of an invited lecture held at the Journ\'ees Relativistes 96.)",9610019v1 1997-03-06,Mass formulae for a class of nonrotating black holes,"In the presence of a Killing symmetry, various self-gravitating field theories with massless scalars (moduli) and vector fields reduce to sigma-models, effectively coupled to 3-dimensional gravity. We argue that this particular structure of the Einstein-matter equations gives rise to quadratic relations between the asymptotic flux integrals and the area and surface gravity (Hawking temperature) of the horizon. The method is first illustrated for the Einstein-Maxwell system. A derivation of the quadratic formula is then also presented for the Einstein-Maxwell-axion-dilaton model, which is relevant to the bosonic sector of heterotic string theory.",9703015v1 1998-05-15,On rotational excitations and axial deformations of BPS monopoles and Julia-Zee dyons,"It is shown that Julia-Zee dyons do not admit slowly rotating excitations. This is achieved by investigating the complete set of stationary excitations which can give rise to non-vanishing angular momentum. The relevant zero modes are parametrized in a gauge invariant way and analyzed by means of a harmonic decomposition. Since general arguments show that the solutions to the linearized Bogomol'nyi equations cannot contribute to the angular momentum, the relevant modes are governed by a set of electric and a set of non self-dual magnetic perturbation equations. The absence of axial dipole deformations is also established.",9805061v1 2001-05-22,Semiclassical evidence for the BGS-conjecture,"Recently, M. Sieber and K. Richter achieved a breakthrough towards a proof of the BGS-conjecture by calculating semiclassically a first correction to the diagonal approximation of the orthogonal form factor for geodesic flow on a Riemann surface of constant negative curvature. In this note, we try to generalize the arguments. However, the solution proposed is not yet correct, because also other geometries must be taken into account.",0105052v3 2001-06-22,Near action degeneracy of periodic orbits in systems with non-conventional time reversal,"Recently, Sieber and Richter calculated semiclassically a first off-diagonal contribution to the orthogonal form factor for a billiard on a surface of constant negative curvature by considering orbit pairs having almost the same action. For a generalization of this derivation to systems invariant under non-conventional time reversal symmetry, which also belong to the orthogonal symmetry class, we show in this paper that it is necessary to redefine the configuration space in an appropriate way.",0106035v1 2011-10-13,Berry-curvatures and anomalous Hall effect in Heusler compounds,"Berry curvatures are computed for a set of Heusler compounds using density functional (DF) calculations and the wave functions that DF provide. The anomalous Hall conductivity is obtained from the Berry curvatures. It is compared with experimental values in the case of Co$_2$CrAl and Co$_2$MnAl. A notable trend cannot be seen but the range of values is quite enormous. The results for the anomalous Hall conductivities and their large variations can be qualitatively understood by means of the band structure and the Fermi-surface topology.",1110.2878v1 2012-06-06,Probing the superconducting state of the Heusler supercoductor: ZrNi$_2$Ga,"Using both muon spin rotation and muon spin relaxation, the superconducting ground state of the Heusler superconductor {ZrNi$_2$Ga} has been studied. The temperature dependence of the magnetic penetration depth of {ZrNi$_2$Ga} is consistent with a single isotropic gap s-wave BCS superconductor. The gap energy is \Delta(0)=0.44(1) meV and the magnetic penetration depth, \lambda(0), is 310(5) nm. Furthermore, we show evidence of a possible cross-over from an square flux line lattice to a hexagonal lattice at low temperatures. No evidence of time reversal symmetry breaking has been observed as might be expected for a half metal superconductor.",1206.1182v1 2012-10-19,Search for spin gapless semiconductors: The case of inverse Heusler compounds,"We employ ab-initio electronic structure calculations to search for spin gapless semiconductors, a recently identified new class of materials, among the inverse Heusler compounds. The occurrence of this property is not accompanied by a general rule and results are materials specific. The six compounds identified show semiconducting behavior concerning the spin-down band structure and in the spin-up band structure the valence and conduction bands touch each other leading to 100% spin-polarized carriers. Moreover these six compounds should exhibit also high Curie temperatures and thus are suitable for spintronics applications.",1210.5355v1 2013-09-25,Half metallic state and magnetic properties versus the lattice constant in Ti\raisebox{-.2ex}{\scriptsize 2}CoSn Heusler compound: an ab initio study,"The half metallic properties of Ti\raisebox{-.2ex}{\scriptsize 2}CoSn full-Heusler compound is studied within the framework of the density functional theory with the Perdew Burke Ernzerhof generalized gradient approximation (GGA). Structural optimization was performed and the calculated equilibrium lattice constant is 6.340 A. The spin up band of compound has metallic character and spin down band is semiconducting with an indirect gap of 0.598 eV at equilibrium lattice constant. For the lattice parameter, ranging from 6.193 to 6.884 A the compound presents 100% spin polarization and a total magnetic moment of 3$\mu_{B}$.",1309.6437v1 2014-11-26,Theoretical investigations of electronic structure and magnetism in Zr2CoSn full-Heusler compound,"The half-metallic properties of a new and promising full-Heusler compound, Zr2CoSn, are investigated by means of ab initio calculations within the Density Functional Theory framework. The ferromagnetic ordered Hg2CuTi-type crystal structure is energetically favorable and the optimized lattice parameter is 6.76 A. The total magnetic moment calculated is 3 uB/f.u. and follows a typical Slater-Pauling dependence. The half metallicity disappears if the unit cell volume is contracted by 5 %.",1411.7154v1 2018-04-01,"First-principles study on thermoelectric properties of half-Heusler compounds CoMSb(M=Sc, Ti, V, Cr, and Mn)","We have performed systematic density functional calculations and evaluated thermoelectric properties, See- beck coefficient and anomalous Nernst coefficient of half-Heusler comounds CoMSb(M=Sc, Ti, V, Cr, and Mn). The carrier concentration dependence of Seebeck coefficients in nonmagnetic compounds are in good agreement with experimental values. We found that the half-metallic ferromagnetic CoMnSb show large anomalous Nernst effect originating from Berry curvature at the Brillouin zone boundary. These results help to understanding for the mechanism of large anomalous Nernst coefficient and give us a clue to design high performance magnetic thermoelectric materials.",1804.00297v1 2022-12-19,Chiral surface superconductivity in half-Heusler semimetals,"We propose the metallic and weakly dispersive surface states of half-Heusler semimetals as a possible domain for the onset of unconventional surface superconductivity ahead of the bulk transition. Using density functional theory (DFT) calculations and the random phase approximation (RPA), we analyse the surface band structure of LuPtBi and its propensity towards Cooper pair formation induced by screened electron-electron interactions in the presence of strong spin-orbit coupling. Over a wide range of model parameters, we find an energetically favoured chiral superconducting condensate featuring Majorana edge modes, while low-dimensional order parameter fluctuations trigger time-reversal symmetry breaking to precede the superconducting transition.",2212.09786v1 2013-09-07,Defects and hyperfine interactions in binary Fe-Al alloys studied by positron annihilation and Mossbauer spectroscopies,"The defects, the behavior of 3d electrons and the hyperfine interactions in binary Fe-Al alloys with different Al contents have been studied by the measurements of positron lifetime spectra, coincidence Doppler broadening spectra of positron annihilation radiation and Mossbauer spectra. The results show that on increasing the Al content in Fe-Al alloys, the mean positron lifetime of the alloys increase, while the mean electron density of the alloys decrease. The increase of Al content in binary Fe-Al alloys will decrease the amount of unpaired 3d electrons; as a consequence the probability of positron annihilation with 3d electrons and the hyperfine field decrease rapidly. Mossbauer spectra of binary Fe-Al alloys with Al content less than 25at% show discrete sextets, these alloys give ferromagnetic contribution at room temperature. The M\""ossbauer spectrum of Fe70Al30 shows a broad singlet. As Al content higher than 40 at%, the M\""ossbauer spectra of these alloys are singlet, that is, the alloys are paramagnetic. The behavior of 3d electron and its effect on the hyperfine field of the binary Fe-Al alloy has been discussed.",1309.2673v1 2014-10-02,Phase stability of ternary fcc and bcc Fe-Cr-Ni alloys,"The phase stability of fcc and bcc magnetic binary Fe-Cr, Fe-Ni, Cr-Ni alloys and ternary Fe-Cr-Ni alloys is investigated using a combination of density functional theory (DFT), Cluster Expansion (CE) and Magnetic Cluster Expansion (MCE). Energies, magnetic moments, and volumes of more than 500 alloy structures are evaluated using DFT, and the most stable magnetic configurations are compared with experimental data. Deviations from the Vegard law in fcc Fe-Cr-Ni alloys, associated with non-linear variation of atomic magnetic moments as functions of alloy composition, are observed. Accuracy of the CE model is assessed against the DFT data, where for ternary alloys the cross-validation error is smaller than 12 meV/atom. A set of cluster interaction parameters is defined for each alloy, where it is used for predicting new ordered alloy structures. Fcc Fe2CrNi phase with Cu2NiZn-like structure is predicted as the global ground state with the lowest chemical ordering temperature of 650K. DFT-based Monte Carlo (MC) simulations are used for assessing finite temperature fcc-bcc phase stability and order-disorder transitions in Fe-Cr-Ni alloys. Enthalpies of formation of ternary alloys calculated from MC simulations at 1600K combined with magnetic correction derived from MCE are in excellent agreement with experimental values measured at 1565K. Chemical order is analysed, as a function of temperature and composition, in terms of the Warren-Cowley short-range order (SRO) parameters and effective chemical pairwise interactions.",1410.0548v2 2020-05-11,"Microstructure, mechanical properties and aging behaviour of nanocrystalline copper-beryllium alloy","A complex study of aging kinetics for both coarse-grained and nanostructured by severe plastic deformation Cu -- 2 wt% Be alloy is reported. It is shown that aging of a coarse-grained alloy leads to continuous formation of nanosized CuBe body centred cubic (bcc, CsCl -- type) semi-coherent particles with the {220} Cu // {200} CuBe crystallographic orientation relationship. These particles created significant internal stress fields and became obstacles for dislocation glide that resulted in a change in the hardness from 95 Vickers hardness (HV) for the solubilized alloy to 400 HV for the aged one. The severe plastic deformation led to the formation of a single-phase nanograined microstructure with an average grain size of 20 nm and 390 HV. It was found that this grain size was slightly driven by grain boundary segregation. Further aging of the nanocrystalline alloy led to the discontinuous formation of precipitates on the former Cu grain boundaries and skipping of metastable phases. Significant age hardening with a maximum hardness of 466 HV for the aged nanostructured alloy was observed. Mechanical tests result revealed a strong influence of microstructure and further aging on strength capability of the alloy for both coarse-grained and nanostructured alloy. A good thermal stability in the nanostructured alloy was also noticed. Theoretical calculations of the hardness value for the CuBe phase are provided. It was shown that Be as a light alloying elements could be used for direct change of microstructure of severely deformed copper alloys.",2005.04976v1 2017-10-13,Unusual negative formation enthalpies and atomic ordering in isovalent alloys of transition metal dichalcogenide monolayers,"Common substitutional isovalent semiconductor alloys usually form disordered metastable phases with positive excess formation enthalpies ({\Delta}H). In contrast, monolayer alloys of transition metal dichalcogenides (TMDs) MX2 (M = Mo, W; X = S, Se) always have negative {\Delta}H, suggesting atomic ordering, which is, however, not yet experimentally observed. Using first-principles calculations, we find that the negative {\Delta}H of cation-mixed TMD alloys results from the charge transfer from weak Mo-X to nearest strong W-X bonds and the negative {\Delta}H of anion-mixed TMD alloys comes from the larger energy gain due to the charge transfer from Se to nearest S atoms than the energy cost due to the lattice mismatch. Consequently, cation-mixed and anion-mixed alloys should energetically prefer to have Mo-X-W and S-M-Se ordering, respectively. The atomic ordering, however, is only locally ordered but disordered in the long range due to the symmetry of TMD monolayers, as demonstrated by many energetically degenerate structures for given alloy compositions. Besides, the local ordering and disordering effects on the macroscopic properties such as bandgaps and optical absorptions are negligible, making the experimental observation of locally ordered TMD alloys challenging. We propose to take the advantage of microscopic properties such as defects which strongly depend on local atomic configurations for experiments to identify the disordering and local ordering in TMD alloys. Finally, quaternary TMD alloys by mixing both cations and anions are studied to have a wide range of bandgaps for optoelectronic applications. Our work is expected to help the formation and utilization of TMD alloys.",1710.05064v1 2024-01-15,"Impact of boron atom clustering on the electronic structure of (B,In)N alloys","Tailoring the electronic and optical properties of nitride-based alloys for optoelectronic applications in the ultraviolet and red spectral range has attracted significant attention in recent years. Adding boron nitride (BN) to indium gallium nitride, (In,Ga)N, alloys, can help to control the lattice mismatch between (In,Ga)N and GaN and may thus allow reduction of strain related defect formation. However, understanding of the impact of BN on the electronic properties of III-N alloys, in particular the influence of experimentally observed boron atom clustering, is sparse. This work presents first-principles calculations investigating the electronic properties of (B,In)N alloys with boron contents between 2% and 7%. Special attention is paid to the impact of the alloy microstructure. While the results show that the lattice constants of such alloys largely agree with lattice constants determined from a Vegard approximation, the electronic properties strongly depend on the local boron atom configurations. For instance, if boron atoms are dispersed throughout the structure and are not sharing nitrogen atoms, the band gap of (B,In)N alloys is largely unaffected and stays close to the gap of pristine InN. However, in the case of boron atom clustering, e.g., when boron atoms are sharing nitrogen atoms, the band gap can be strongly reduced, often leading to a metallic state in (B,In)N alloys. These strong band gap reductions are mainly driven by carrier localization effects in the valence band. The calculations thus show that the electronic structure of (B,In)N alloys strongly depends on the alloy microstructure and that boron atom clustering plays an important role in understanding the electronic and optical properties of these emerging materials.",2401.07623v1 2010-02-28,Tunable Multifunctional Topological Insulators in Ternary Heusler Compounds,"Recently the Quantum Spin Hall effect (QSH) was theoretically predicted and experimentally realized in a quantum wells based on binary semiconductor HgTe[1-3]. QSH state and topological insulators are the new states of quantum matter interesting both for fundamental condensed matter physics and material science[1-11]. Many of Heusler compounds with C1b structure are ternary semiconductors which are structurally and electronically related to the binary semiconductors. The diversity of Heusler materials opens wide possibilities for tuning the band gap and setting the desired band inversion by choosing compounds with appropriate hybridization strength (by lattice parameter) and the magnitude of spin-orbit coupling (by the atomic charge). Based on the first-principle calculations we demonstrate that around fifty Heusler compounds show the band inversion similar to HgTe. The topological state in these zero-gap semiconductors can be created by applying strain or by designing an appropriate quantum well structure, similar to the case of HgTe. Many of these ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the rare earth element Ln which can realize additional properties ranging from superconductivity (e. g. LaPtBi[12]) to magnetism (e. g. GdPtBi[13]) and heavy-fermion behavior (e. g. YbPtBi[14]). These properties can open new research directions in realizing the quantized anomalous Hall effect and topological superconductors.",1003.0193v1 2015-04-07,Thermal Expansion of Ni-Ti-Sn Heusler and Half-Heusler Materials from First Principles Calculations and Experiments,"We coupled first principles calculations and the quasiharmonic approximation combined with experiments (X-Ray diffraction and dilatometry measurements) to determine the thermal properties of NiTiSn (half-Heusler) and Ni2TiSn (Heusler) compounds. These properties are important especially if they are to be used in thermoelectric applications. First, the calculation of their mode Gruneisen parameter shows that it is positive throughout the first Brillouin zone. This suggests that these compounds undergo a regular thermal expansion. Then, the calculation of the Ni2TiSn thermal expansion shows an excellent agreement, even in the high temperature range, with our high energy powder X-Ray diffraction measurements (ESRF) and dilatometry experiments. In the case of NiTiSn, this agreement is less impressive. This could be due to stronger phonon-phonon interactions that are not considered within the quasiharmonic approximation, but also to the difficulty of making high-quality NiTiSn samples. Finally, the constant-pressure and constant-volume heat capacities have been calculated for both compounds and compared with the experimental data reported in the literature. In particular, we have decomposed the constant-volume heat capacity of Ni2TiSn into a purely electronic and a phonon-mediated contribution, and we discuss each of them.",1504.01606v1 2016-04-06,Anomalous Hall effect in Weyl semimetal half Heusler compounds RPtBi (R = Gd and Nd),"Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R= rare earth) have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly and planar Hall effect have been observed experimentally. Here, we report on an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 ohm-1cm-1 and an anomalous Hall angle as large as 23%. Muon spin resonance (mu-SR) studies of GdPtBi indicate a sharp antiferromagnetic transition (T_N) at 9 K without any noticeable magnetic correlations above T_N. Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange-splitting of the electronic bands at or near to the Fermi energy which is the source of the chiral anomaly and the AHE.",1604.01641v2 2018-01-09,Epitaxial Heusler Superlattice Co2MnAl/Fe2MnAl with Perpendicular Magnetic Anisotropy and Termination-Dependent Half-Metallicity,"Single-crystal Heusler atomic-scale superlattices that have been predicted to exhibit perpendicular magnetic anisotropy and half-metallicity have been successfully grown by molecular beam epitaxy. Superlattices consisting of full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers with high cobalt or high iron concentrations for samples grown near room temperature on GaAs (001). Superlattice structures grown with an excess of aluminum had significantly lower thin film shape anisotropy and resulted in an out-of-plane spin reorientation transition at temperatures below 200 K for samples grown on GaAs (001). Synchrotron-based spin resolved photoemission spectroscopy found that the superlattice structure improves the Fermi level spin polarization near the X point in the bulk Brillouin zone. Stoichiometric Co$_2$MnAl terminated superlattice grown on MgO (001) had a spin polarization of 95%, while a pure Co$_2$MnAl film had a spin polarization of only 65%.",1801.02787v1 2018-01-11,"Structural, elastic, electronic, magnetic and thermoelectric properties of new quaternary Heusler compounds CoZrMnX (X=Al, Ga, Ge, In)","We have performed a comprehensive set of first principles calculations to study the structural, elastic, electronic, magnetic and transport properties of new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In). The results showed that all the quaternary Heusler compounds were stable in Type(I) structure. CoZrMnX are elastically stable and relatively hard materials. CoZrMnAl, CoZrMnGa, and CoZrMnIn are found to be ductile and CoZrMnGe is brittle in nature. The calculated Debye temperatures of all compounds are relatively high. The electronic structure calculations reveal that CoZrMnAl is nearly half metallic, CoZrMnGa and CoZrMnIn are metallic, and CoZrMnGe is a narrow indirect bandgap semiconductor. The calculated magnetic properties implies that CoZrMnAl, CoZrMnGa, and CoZrMnIn are ferromagnetic while CoZrMnGe is non-magnetic material. The CoZrMnAl is highly spin-polarized (96%) and CoZrMnGe is non-spin-polarized. Seebeck coefficent (S) in CoZrMnGe is relatively high (-106 {\mu}V/K at 650K) due to its semiconducting nature. The calculated thermoelectric figure of merit CoZrMnGe is 0.1 at 600K and for CoZrMnIn it is also 0.1 at 900 K. We hope our interesting results will inspire experimentalist to synthesis the new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In).",1801.03719v1 2018-03-01,Observation of Dirac state in half-Heusler material YPtBi,"The prediction of non-trivial topological electronic states hosted by half-Heusler compounds makes them prime candidates for discovering new physics and devices as they harbor a variety of electronic ground states including superconductivity, magnetism, and heavy fermion behavior. Here we report normal state electronic properties of a superconducting half-Heusler compound YPtBi using angle-resolved photoemission spectroscopy (ARPES). Our data reveal the presence of a Dirac state at the zone center of the Brillouin zone at 500 meV below the chemical potential. We observe the presence of multiple Fermi surface pockets including two concentric hexagonal and six half oval shaped pockets at the gamma and K points of the Brillouin zone, respectively. Furthermore, our measurements show Rashba-split bands and multiple surface states crossing the chemical potential which are supported by the first-principles calculations. Our finding of a Dirac state in YPtBi plays a significant role in establishing half-Heusler compounds as a new potential platform for novel topological phases and explore their connection with superconductivity.",1803.00589v1 2017-02-27,Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: a systematic study,"With a view to the design of hard magnets without rare earths we explore the possibility of large magnetocrystalline anisotropy energies in Heusler compounds that are unstable with respect to a tetragonal distortion. We consider the Heusler compounds Fe$_2$YZ with Y = (Ni, Co, Pt), and Co$_2$YZ with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find that for the Co$_2$NiZ, Co$_2$PtZ, and Fe$_2$PtZ families the cubic phase is always, at $T=0$, unstable with respect to a tetragonal distortion, while, in contrast, for the Fe$_2$NiZ and Fe$_2$CoZ families this is the case for only 2 compounds -- Fe$_2$CoGe and Fe$_2$CoSn. For all compounds in which a tetragonal distortion occurs we calculate the MAE finding remarkably large values for the Pt containing Heuslers, but also large values for a number of the other compounds (e.g. Co$_2$NiGa has an MAE of -2.11~MJ/m$^3$). The tendency to a tetragonal distortion we find to be strongly correlated with a high density of states at the Fermi level in the cubic phase. As a corollary to this fact we observe that upon doping compounds for which the cubic structure is stable such that the Fermi level enters a region of high DOS, a tetragonal distortion is induced and a correspondingly large value of the MAE is then observed.",1702.08150v1 2019-09-27,Surface Reconstructions of Heusler Compounds in the Ni-Ti-Sn (001) System,"As progress is made on thin-film synthesis of Heusler compounds, a more complete understanding of the surface will be required to control their properties, especially as functional heterostructures are explored. Here, the surface reconstructions of semiconducting half-Heusler NiTiSn(001), and Ni1+xTiSn(001) (x=0.0-1.0) are explored as a way to optimize growth conditions during molecular beam epitaxy. Density functional theory (DFT) calculations were carried out to guide the interpretation of the experimental results. For NiTiSn(001) a c(2x2) surface reconstruction was observed for Sn rich samples, while a (1x1) unreconstructed surface was observed for Ti-rich samples. A narrow range around 1:1:1 stoichiometry exhibited a (2x1) surface reconstruction. Electrical transport is used to relate the observed reflection high energy electron diffraction (RHEED) pattern during and after growth with carrier concentration and stoichiometry. Scanning tunneling microscopy and RHEED were used to examine surface reconstructions, the results of which are in good agreement with density functional calculations. X-ray photoelectron spectroscopy was used to determine surface termination and stoichiometry. Atomic surface models are proposed, which suggest Sn-dimers form in reconstructed Ni1+xTiSn(001) half-Heusler surfaces (x<0.25) with a transition to Ni terminated surfaces for x > 0.25.",1909.12487v1 2020-02-11,A simple model for vacancy order and disorder in defective half-Heusler systems,"Defective half-Heusler systems X(1-x)YZ with large amounts of intrinsic vacancies, such as Nb(1-x)CoSb, Ti(1-x)NiSb and V(1-x)CoSb, are a group of promising thermoelectric materials. Even with high vacancy concentrations they maintain the average half-Heusler crystal structure. These systems show high electrical conductivity but low thermal conductivity arising from an ordered YZ lattice, which conducts electrons, while the large amounts of vacancies on the X sublattice effectively scatters phonons. Using electron scattering it was recently observed that in addition to Bragg diffraction from the average cubic half-Heusler structure, some of these samples show broad diffuse scattering indicating short-range vacancy order while other samples show sharp additional peaks, indicating long-range vacancy ordering. Here we show that both the short and long-range ordering can be explained using the same simple model, which assumes that vacancies on the X-sublattice avoid each other. The samples showing long-range vacancy order are in agreement with the predicted ground-state of the model, while short-range order samples are quenched high-temperature states of the system. A previous study showed that changes in sample stoichiometry affect whether the short or long-range vacancy structure is obtained, but the present model suggests that thermal treatment of samples should allow controlling the degree of vacancy order, and thereby the thermal conductivity, without changes in composition. This is important as the composition also dictates the amount of electrical carriers. Independent control of electrical carrier concentration and degree of vacancy order should allow further improvements in the thermoelectric properties of these systems.",2002.04281v2 2020-11-16,A high throughput search of efficient thermoelectric half-Heusler compounds,"Half-Heusler compounds have emerged as promising thermoelectric materials that offer huge compositional space to tune their thermoelectric performance. A class of stable half Heusler compounds formed from elements of three specific groups in the periodic table viz. X$_{p}$X$'_{1-p}$Y$_{q}$Y$'_{1-q}$Z$_{r}$Z$'_{1-r}$ (with X, X$'$= Ti, Zr, Hf, Y, Y$'$ = Ni, Pd, Pt and Z, Z$'$ = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and 1) via various stoichiometric isoelectronic elemental substitution at the X, Y and Z sites respectively is investigated. Intelligent filters are employed at each step of our high throughput density functional theory calculations to filter compounds with improved figure of merit. While confirming several known results, the calculations also reveal unknown pathways to improve the thermoelectric performance of the compound class. The 50% X as well as Z site substitution of the parent Heusler individually are found to marginally enhance the power factor for both the $p$- and $n$-type doping, while leading to considerable enhancement in the figure of merit (by $\sim$24 %) specifically due to lowering of the lattice thermal conductivity because of increase in lattice disorder in approximately the same cell volume. Furthermore, the present study confirms the experimental scenario that Y site substitution does not lead to enhancement of the powerfactor because of the breaking of band degeneracies at the high symmetry points. This work will serve as a consolidated cost effective guideline for experimentalist working with this compound class on enhancing the powerfactor and figure of merit of the compositions.",2011.08134v1 2021-06-27,Ferromagnetic Cr4PtGa17: A Novel Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice,"We describe the crystal structure and elementary magnetic properties of a previously unreported ternary intermetallic compound, Cr4PtGa17, which crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group R3m. The crystal structure is closely related to those of XYZ half-Heusler compounds, where X, Y and Z are reported to be single elements only, occupying three different face-centered cubic sublattices. The new material, Cr4PtGa17, can be most straightforwardly illustrated by writing the formula as (PtGa2)(Cr4Ga14)Ga (X=PtGa2, Y = Cr4Ga14, Z = Ga), that is, the X and Y sites are occupied by clusters instead of single elements. The magnetic Cr occupies a breathing pyrochlore lattice. Ferromagnetic ordering is found below TC ~61 K, by both neutron diffraction and magnetometer studies, with a small, saturated moment of ~0.25 muB/Cr observed at 2 K, making Cr4PtGa17 the first ferromagnetically ordered material with a breathing pyrochlore lattice. A magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that the material has a nearly-half-metallic electronic structure. The new material, Cr4PtGa17, the first realization of both a half-Heusler-type structure and a breathing pyrochlore lattice, might pave a new way to achieve novel types of half-Heusler compounds.",2106.14296v2 2022-09-28,First Principles Study of the Electronic Structure of the Ni$_2$MnIn/InAs and Ti$_2$MnIn/InSb interfaces,"We present a first-principles study of the electronic and magnetic properties of epitaxial interfaces between the Heusler compounds Ti$_2$MnIn and Ni$_2$MnIn and the III-V semiconductors, InSb and InAs, respectively. We use density functional theory (DFT) with a machine-learned Hubbard $U$ correction determined by Bayesian optimization. We evaluate these interfaces for prospective applications in Majorana-based quantum computing and spintronics. In both interfaces, states from the Heusler penetrate into the gap of the semiconductor, decaying within a few atomic layers. The magnetic interactions at the interface are weak and local in space and energy. Magnetic moments of less than 0.1 $\mu_B$ are induced in the two atomic layers closest to the interface. The induced spin polarization around the Fermi level of the semiconductor also decays within a few atomic layers. The decisive factor for the induced spin polarization around the Fermi level of the semiconductor is the spin polarization around the Fermi level in the Heusler, rather than the overall magnetic moment. As a result, the ferrimagnetic narrow-gap semiconductor Ti$_2$MnIn induces a more significant spin polarization in the InSb than the ferromagnetic metal Ni$_2$MnIn induces in the InAs. This is explained by the position of the transition metal $d$ states in the Heusler with respect to the Fermi level. Based on our results, these interfaces are unlikely to be useful for Majorana devices but could be of interest for spintronics.",2209.14101v3 2023-02-07,Colossal anomalous Hall and Nernst effect from the breaking of nodal-line symmetry in Cu2CoSn Weyl semimetal: A first-principles study,"The presence of topological band crossings near the Fermi energy is essential for the realization of large anomalous transport properties in the materials. The topological semimetals (TSMs) host such properties owing to their unique topological band structure such as Weyl points or nodal lines (NLs), that is protected by certain symmetries of the crystal. When the NLs break out in the system due to perturbation in Hamiltonian, a large Berry curvature arises in the surrounding area of the gapped NL. In the present work, we studied anomalous transport properties of Cu2CoSn compound, which has a cubic Heusler crystal structure (space group: Fm-3m). The Cu2CoSn full Heusler compound possesses three NLs in the absence of spin-orbit coupling close to the Fermi level. These NLs gap out with the consideration of the SOC and a large Berry curvature observed along the gapped NLs. The integral of Berry curvature gives the intrinsic anomalous Hall conductivity (AHC) about 1003 S/cm and the anomalous Nernst conductivity (ANC) of about 3.98 A/m-K at the Fermi level. These values of AHC and ANC are comparable to the largest reported values for the Co2MnGa Heusler compound. Therefore, Cu2CoSn becomes a newborn member of the family of full Heusler compounds, which possesses giant AHC and ANC that can be useful for the spintronics application.",2302.03279v1 2023-02-09,Spin-polarized two-dimensional electron/hole gas at the interface of non-magnetic semiconducting half-Heusler compounds: Modified Slater-Pauling rule for half-metallicity at the interface,"Half-Heusler compounds with 18 valence electrons per unit cell are well-known non-magnetic semiconductors. Employing first-principles electronic band structure calculations, we study the interface properties of the half-Heusler heterojunctions based on FeVSb, CoTiSb, CoVSn, and NiTiSn compounds, which belong to this category of materials. Our results show that several of these heterojunction interfaces become not only metallic but also magnetic. The emergence of spin-polarization is accompanied by the formation of two-dimensional electron gas (2DEG) or hole gas (2DHG) at the interface. We qualitatively discuss the origin of the spin polarization at the interfaces on the basis of the Stoner model. For the cases of magnetic interfaces where half-metallicity is also present, we propose a modified Slater-Pauling rule similar to the one for bulk half-metallic half-Heusler compounds. Additionally, we calculate exchange parameters, Curie temperatures and magnetic anisotropy energies for magnetic interfaces. Our study, combined with the recent experimental evidence for the presence of 2DEG at CoTiSb/NiTiSn heterojunctions might motivate future efforts and studies toward the experimental realization of devices using the proposed heterojunctions.",2302.04563v1 2023-03-17,Intrinsic and extrinsic anomalous transport properties of Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl from first principles,"Recently, Heusler ferromagnets have been found to exhibit unconventional anomalous electric, thermal, and thermoelectric transport properties. In this study, we employed first-principles density functional theory calculations to systematically investigate both intrinsic and extrinsic contributions to the anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and anomalous thermal Hall effect (ATHE) in two Heusler ferromagnets: Fe$_2$CoAl and Fe$_2$NiAl. Our analysis reveals that the extrinsic mechanism originating from disorder dominates the AHE and ATHE in Fe$_2$CoAl , primarily due to the steep band dispersions across the Fermi energy and corresponding high longitudinal electronic conductivity. Conversely, the intrinsic Berry phase mechanism, physically linked to nearly flat bands around the Fermi energy and gapped by spin-orbit interaction band crossings, governs the AHE and ATHE in Fe$_2$NiAl. With respect to ANE, both intrinsic and extrinsic mechanisms are competing in Fe$_2$CoAl as well as in Fe$_2$NiAl. Furthermore, Fe$_2$CoAl and Fe$_2$NiAl exhibit tunable and remarkably pronounced anomalous transport properties. For instance, the anomalous Nernst and anomalous thermal Hall conductivities in Fe$_2$NiAl attain giant values of 8.29 A/Km and 1.19 W/Km, respectively, at room temperature. To provide a useful comparison, we also thoroughly investigated the anomalous transport properties of Co$_2$MnGa. Our findings suggest that Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl are promising candidates for spintronics and spin-caloritronics applications.",2303.09812v2 2023-06-07,Searching for ductile superconducting Heusler X2YZ compounds,"Heusler compounds have always attracted a great deal of attention from researchers thanks to a wealth of interesting properties for technological applications. They are intermetallic ductile compounds, and some of them have been found to be superconducting. With this in mind, we perform an extensive study of the superconducting and elastic properties of the cubic (full-)Heusler family. Starting from thermodynamically stable compounds, we use ab initio methods for the calculation of the phonon spectra, electron-phonon couplings, superconducting critical temperatures and elastic tensors. By analyzing the statistical distributions of these properties and comparing them to anti-perovskites we recognize universal behaviors that should be common to all conventional superconductors while others turn out to be specific to the material family. The resulting data is used to train interpretable and predictive machine learning models, that are used to extend our knowledge of superconductivity in Heuslers and to provide an interpretation of our results. In total, we discover a total of 8 hypothetical materials with critical temperatures above 10 K, to be compared with the current record of Tc = 4.7 K in this family. Furthermore, we expect most of these materials to be highly ductile, making them potential candidates for the manufacture of wires and tapes for superconducting magnets.",2306.04439v1 2023-09-14,Chemical-substitution-driven giant anomalous Hall and Nernst effects in magnetic cubic Heusler compounds,"Chemical substitution efficiently optimizes the physical properties of Heusler compounds, especially their anomalous transport properties, including anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC). This study systematically investigates the effect of chemical substitution on AHC and ANC in 1493 magnetic cubic Heusler compounds using high-throughput first-principles calculations. Notable trends emerge in Co- and Rh-based compounds, where chemical substitution effectively enhances the AHC and ANC. Intriguingly, certain chemically substituted candidates exhibit outstanding enhancement in AHCs and ANCs, such as (Co$_{0.8}$Ni$_{0.2}$)$_2$FeSn with considerable AHC and ANC values of $-2567.78$ S cm$^{-1}$ and $8.27$ A m$^{-1}$K$^{-1}$, respectively, and (Rh$_{0.8}$Ru$_{0.2}$)$_2$MnIn with an AHC of $1950.49$ S cm$^{-1}$. In particular, an extraordinary ANC of $8.57$ A m$^{-1}$K$^{-1}$ is identified exclusively in Rh$_2$Co$_{0.7}$Fe$_{0.3}$In, nearly double the maximum value of $4.36$ A m$^{-1}$K$^{-1}$ observed in the stoichiometric Rh$_2$CoIn. A comprehensive band structure analysis underscores that the notable enhancement in ANC arises from the creation and modification of the energy-dependent nodal lines through chemical substitution. This mechanism generates a robust Berry curvature, resulting in significant ANCs. These findings emphasize the pivotal role of chemical substitution in engineering high-performance materials, thereby expanding the horizons of transport property optimization within Heusler compounds.",2309.07722v3 2023-10-24,"Tuning the topological character of half-Heusler systems: A comparative study on Y$T$Bi ($T$ = Pd, Pt)","Half-Heusler systems host a plethora of different ground states, especially with non-trivial topology. However, there is still a lack of spectroscopic insight into the corresponding band inversion in this family. In this work, we locally explore the half-Heuslers Y$T$Bi ($T =$ Pt and Pd) by means of scanning tunneling microscopy/spectroscopy. From our analysis of the (120) surface plane, we infer that the increase of the spin--orbit coupling upon going from Pd to Pt is the main player in tuning the surface states from trivial to topologically non-trivial. Our measurements unveil a ($2 \times 1$) reconstruction of the (120) surface of both systems. Using density functional theory calculations, we show that the observed different behavior of the local density of states near the Fermi level in these two materials is directly related to the presence of metallic surface states. Our work sheds new light on a well known tunable family of materials and opens new routes to explore the presence of topological states of matter in half-Heusler systems and its microscopic observation.",2310.15708v1 2023-11-10,Strong-coupling superconductivity of the Heusler-type compound ScAu2Al: Ab-initio studies,"The ScAu$_2$Al superconducting Heusler-type compound was recently characterized to have the highest critical temperature of $T_c = 5.12$ K and the strongest electron-phonon coupling among the Heusler family. In this work, the electronic structure, phonons, electron-phonon coupling, and superconductivity of ScAu$_2$Al are studied using \textit{ab initio} calculations. The spin-orbit coupling significantly changes the electronic structure removing the van Hove singularity from the vicinity of the Fermi level. In the phonon spectrum, low frequency acoustic modes, additionally softened by the spin-orbit interaction, strongly couple with electrons, leading to the electron-phonon coupling constant $\lambda=1.25$, a record high among Heuslers. The density functional theory for superconductors is then used to analyze superconducting {state in this two-band superconductor}. The effect of spin fluctuations (SF) on superconductivity is also analyzed. The calculated critical temperatures of $T_c = 5.16$ K (4.79 K with SF) agree very well with the experiment, confirming the electron-phonon mechanism of superconductivity and showing a weak spin-fluctuations effect. The superconducting gaps formed on two Fermi surface sheets exhibit moderate anisotropy. Their magnitudes confirm the strong coupling regime, as the reduced average values are $2\Delta_1/k_BT_c \simeq 4.1$ and $2\Delta_2/k_BT_c \simeq 4.3$. Anisotropy of the gaps and large spread in their values significantly affect the calculated quasiparticle density of states.",2311.06075v3 2006-11-07,"Calculated electronic and magnetic properties of the half-metallic, transition metal based Heusler compounds","In this work, results of {\it ab-initio} band structure calculations for $A_2BC$ Heusler compounds that have $A$ and $B$ sites occupied by transition metals and $C$ by a main group element are presented. This class of materials includes some interesting half-metallic and ferromagnetic properties. The calculations have been performed in order to understand the properties of the minority band gap and the peculiar magnetic behavior found in these materials. Among the interesting aspects of the electronic structure of the materials are the contributions from both $A$ and $B$ atoms to states near the Fermi energy and to the total magnetic moment. The magnitude of the total magnetic moment, which depends as well on the kind of $C$ atoms, shows a trend consistent with the Slater-Pauling type behavior in several classes of these compounds. The localized moment in these magnetic compounds resides at the $B$ site. Other than in the classical Cu$_2$-based Heusler compounds, the $A$ atoms in Co$_2$, Fe$_2$, and Mn$_2$ based compounds may contribute pronounced to the total magnetic moment.",0611179v1 2009-04-27,Exchange stiffness in Co$_{2}$-based Heusler compounds,"We determine the spin wave exchange stiffness $D$ and the exchange constant $A$ for the full Heusler compound \CFS using Brillouin light scattering spectroscopy. We find an extraordinarily large value of $D=715\pm20$ meV \AA$^2$ ($A=31.5\pm1.0$ pJ/m) which is, to the best of our knowledge, only surpassed by the intermetallic compound Fe$_{53}$Co$_{47}$ (J. Appl. Phys. \textbf{75}, 7021 (1994)). Furthermore, we provide a systematization of the exchange stiffnesses determined for a variety of Co$_2$-based Heusler compounds. We find that for the investigated compounds, the exchange stiffness is a function of the valence electron concentration and the crystallographic ordering. The exchange stiffness increases when the valence electron concentration and/or the amount of the L2$_1$ ordering increase. A qualitative explanation for the dependence on the valence electron concentration is provided.",0904.4194v1 2010-04-07,Single-Dirac-cone Z2 topological insulator phases in distorted Li2AgSb-class and related quantum critical Li-based spin-orbit compounds,"We have extended our new materials class search for the experimental realization of Z2 topological insulators from binary [Bi2Se3-class, Xia et.al., Nature Phys. 5, 398 (2009)] and the ternary [Half-Heusler class, Lin et.al., arXiv:1003.0155v1 (2010); arXiv:1003.2615v1 (2010)] series to non-Heusler Li-based ternary intermetallic series Li2M'X ($M'$=Cu, Ag, and Au, $X$=Sb and Bi) with CuHg2Ti-type structure. We discovered that the distorted-Li2AgSb is a lightweight compound harboring a 3D topological insulator state with Z2=-1 although the groundstate lies near a critical point, whereas the related Li2CuSb-type compounds are topologically trivial. Non-Heusler ternary Li2M'X series (with a number of variant compounds) we identified here is a new platform for deriving novel stoichiometric compounds, artificial quantum-well/heterostructures, nano-wires, nano-ribbons and nanocrystals. We have grown some of these bulk materials (experimental results will be reported separately).",1004.0999v1 2010-07-31,Half-Heusler Compounds as a New Class of Three-Dimensional Topological Insulators,"Using first-principles calculations within density functional theory, we explore the feasibility of converting ternary half-Heusler compounds into a new class of three-dimensional topological insulators (3DTI). We demonstrate that the electronic structure of unstrained LaPtBi as a prototype system exhibits distinct band-inversion feature. The 3DTI phase is realized by applying a uniaxial strain along the [001] direction, which opens a bandgap while preserving the inverted band order. A definitive proof of the strained LaPtBi as a 3DTI is provided by directly calculating the topological Z2 invariants in systems without inversion symmetry. We discuss the implications of the present study to other half-Heusler compounds as 3DTI, which, together with the magnetic and superconducting properties of these materials, may provide a rich platform for novel quantum phenomena.",1008.0057v1 2010-11-05,Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films,"We correlate simultaneously recorded magnetotransport and spatially resolved magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films micropatterned into Hall bars. Room temperature MOKE images reveal the nucleation and propagation of domains in an externally applied magnetic field and are used to extract a macrospin corresponding to the mean magnetization direction in the Hall bar. The anisotropic magnetoresistance calculated using this macrospin is in excellent agreement with magnetoresistance measurements. This suggests that the magnetotransport in Heusler compounds can be adequately simulated using simple macrospin models, while the magnetoresistance contribution due to domain walls is of negligible importance.",1011.1417v1 2011-07-31,Room-temperature generation of giant pure spin currents using Co$_2$FeSi spin injectors,"Generation, manipulation, and detection of a pure spin current, i.e., the flow of spin angular momentum without a charge current, are prospective approaches for realizing next-generation spintronic devices with ultra low electric power consumptions. Conventional ferromagnetic electrodes such as Co and NiFe have so far been utilized as a spin injector for generating the pure spin currents in nonmagnetic channels. However, the generation efficiency of the pure spin currents is extremely low at room temperature, giving rise to a serious obstacle for device applications. Here, we demonstrate the generation of giant pure spin currents at room temperature in lateral spin valve devices with a highly ordered Heusler-compound Co$_2$FeSi spin injector. The generation efficiency of the pure spin currents for the Co$_2$FeSi spin injectors reaches approximately one hundred times as large as that for NiFe ones, indicating that Heusler-compound spin injectors enable us to materialize a high-performance lateral spin device. The present study is a technological jump in spintronics and indicates the great potential of ferromagnetic Heusler compounds with half metallicity for generating pure spin currents.",1108.0156v2 2011-11-03,Estimation of the spin polarization for Heusler-compound thin films by means of nonlocal spin-valve measurements: Comparison of Co$_{2}$FeSi and Fe$_{3}$Si,"We study room-temperature generation and detection of pure spin currents using lateral spin-valve devices with Heusler-compound electrodes, Co$_{2}$FeSi (CFS) or Fe$_{3}$Si (FS). The magnitude of the nonlocal spin-valve (NLSV) signals is seriously affected by the dispersion of the resistivity peculiarly observed in the low-temperature grown Heusler compounds with ordered structures. From the analysis based on the one-dimensional spin diffusion model, we find that the spin polarization monotonically increases with decreasing the resistivity, which depends on the structural ordering, for both CFS and FS electrodes, and verify that CFS has relatively large spin polarization compared with FS.",1111.0742v2 2012-10-17,GW study of the half-metallic Heusler compounds Co2MnSi and Co2FeSi,"Quasiparticle spectra of potentially half-metallic Co2MnSi and Co2FeSi Heusler compounds have been calculated within the one-shot GW approximation in an all-electron framework without adjustable parameters. For Co2FeSi the many-body corrections are crucial: a pseudogap opens and good agreement of the magnetic moment with experiment is obtained. Otherwise, however, the changes with respect to the density-functional-theory starting point are moderate. For both cases we find that photoemission and x-ray absorption spectra are well described by the calculations. By comparison with the GW density of states, we conclude that the Kohn-Sham eigenvalue spectrum provides a reasonable approximation for the quasiparticle spectrum of the Heusler compounds considered in this work.",1210.4776v1 2012-10-29,Modified Becke-Johnson potential investigation of half-metallic Heusler compounds,"We have investigated the electronic structures of various potentially half-metallic Heusler compounds with the Tran-Blaha modified Becke-Johnson (TB-mBJLDA) potential within the density functional theory. The half-metallic gaps are considerably enhanced with respect to values from the Perdew-Burke-Ernzerhof (PBE) functional. In particular the unoccupied densities of states are modified by mBJLDA, and agreement with experiment is considerably worse than for PBE. The agreement of the densities of states can be improved by reducing the Tran-Blaha parameter c. However, ground state properties such as the hyperfine fields are more accurately described by PBE than by mBJLDA. Despite its success for ionic and covalent semiconductors and insulators, we conclude that mBJLDA is not a suitable approximation for half-metallic Heusler compounds.",1210.7738v1 2012-11-02,Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers,"All-Heusler multilayer structures have been investigated by means of high kinetic x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism, aiming to address the amount of disorder and interface diffusion induced by annealing of the multilayer structure. The studied multilayers consist of ferromagnetic Co$_2$MnGe and non-magnetic Rh$_2$CuSn layers with varying thicknesses. We find that diffusion begins already at comparably low temperatures between 200 $^{\circ}$C and 250 $^{\circ}$C, where Mn appears to be most prone to diffusion. We also find evidence for a 4 {\AA} thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the small magnetoresistance found for current-perpendicular-to-plane giant magneto-resistance devices based on this all-Heusler system.",1211.0489v2 2013-03-03,High spin polarization of the anomalous Hall current in Co-based Heusler compounds,"Based on first principles density functional calculations of the intrinsic anomalous and spin Hall conductivities, we predict that the charge Hall current in Co-based full Heusler compounds Co$_2$XZ (X = Cr and Mn; Z = Al, Si, Ga, Ge, In and Sn) except Co$_2$CrGa would be almost fully spin-polarized even although Co$_2$MnAl, Co$_2$MnGa, Co$_2$MnIn and Co$_2$MnSn do not have a half-metallic band structure. Furthermore, the ratio of the associated spin current to the charge Hall current is slightly larger than 1.0. This suggests that these Co-based Heusler compounds, especially Co$_2$MnAl, Co$_2$MnGa and Co$_2$MnIn which are found to have large anomalous and spin Hall conductivities, might be called anomalous Hall half-metals and could have valuable applications in spintronics such as spin valves as well as magnetoresistive and spin-torque driven nanodevices. These interesting findings are discussed in terms of the calculated electronic band structures, magnetic moments and also anomalous and spin Hall conductivities as a function of the Fermi level.",1303.0509v1 2013-07-11,Large Linear Magnetoresistance and Shubnikov-de Hass Oscillations in Single Crystals of YPdBi Heusler Topological Insulators,"We report the observation of a large linear magnetoresistance (MR) and Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi Heusler topological insulators. Owning to the successfully obtained the high-quality YPdBi single crystals, large non-saturating linear MR of as high as 350% at 5K and over 120% at 300 K under a moderate magnetic field of 7 T is observed. In addition to the large, field-linear MR, the samples exhibit pronounced SdH quantum oscillations at low temperature. Analysis of the SdH data manifests that the high-mobility bulk electron carriers dominate the magnetotransport and are responsible for the observed large linear MR in YPdBi crystals. These findings imply that the Heusler-based topological insulators have superiorities for investigating the novel quantum transport properties and developing the potential applications.",1307.3022v1 2013-07-25,Plasmon dispersions in simple metals and Heusler compounds,"We present a comprehensive study of plasmon dispersions in simple metals and Heusler compounds based on an accurate ab-initio evaluation of the momentum and frequency dependent dielectric function in the random-phase approximation. Using a momentum-dependent tetrahedron method for the computation of the dielectric function, we extract and analyze ""full"" and ""intraband"" plasmon dispersions: The ""full"" plasma dispersion is obtained by including all bands, the intraband plasma dispersion by including only intraband transitions. For the simple metals silver and alu- minum, we show that the intraband plasmon dispersion has an unexpected downward slope and is therefore markedly different from the results of an effective-mass electron-gas model and the full plasmon dispersion. For the two Heusler compounds Co2FeSi and Co2MnSi, we present spectra for the dielectric function, their loss functions and plasmon dispersions. The latter exhibit the same negative intraband plasmon dispersion as found in the simple metals. We also discuss the influence of spin-mixing on the plasmon dispersion.",1307.6844v1 2013-10-17,A new class of topological insulators from I-III-IV half-Heusler compounds with strong band inversion strength,"In this paper, by first principle calculations, we investigate systematically the band topology of a new half-Heusler family with composition of I(A)-III(A)-IV(A). The results clearly show that many of the I-III-IV half-Heusler compounds are in fact promising to be topological insulator candidates. The characteristic feature of these new topological insulators is the naturally strong band inversion strength (up to -2eV) without containing heavy elements. Moreover, we found that both the band inversion strength and the topological insulating gap can be tailored through strain engineering, and therefore would be grown epitaxially in the form of films, and useful in spintronics and other applications.",1310.4696v1 2014-08-25,Nanograined half-Heusler semiconductors as advanced thermoelectrics: an ab-initio high-throughput statistical study,"Nanostructuring has spurred a revival in the field of direct thermoelectric energy conversion. Nanograined materials can now be synthesized with higher figures of merit (ZT) than the bulk counterparts. This leads to increased conversion efficiencies. Despite considerable effort in optimizing the known and discovering the unknown, technology still relies upon a few limited solutions. Here we perform ab-initio modeling of ZT for 75 nanograined compounds obtained by filtering down the 79,057 half-Heusler entries available in the AFLOWLIB.org repository according to electronic and thermodynamic criteria. For many of the compounds the $ZT$s are markedly above those attainable with nanograined IV and III-V semiconductors. About 15% of them may even outperform ZT~2 at high temperatures. Our analysis elucidates the origin of the advantageous thermoelectric properties found within this broad material class. We use machine learning techniques to unveil simple rules determining if a nanograined half-Heusler compound is likely to be a good thermoelectric given its chemical composition.",1408.5859v1 2015-02-06,Long-term stability of phase-separated Half-Heusler compounds,"Half-Heusler (HH) compounds have shown high Figure of merits up to 1.5. The key to these high thermoelectric efficiencies is an intrinsic phase separation, which occurs in multicomponent Half-Heusler compounds and leads to an significantly reduction of the thermal conductivity. For commercial applications, compatible n- and p-type materials are essential and their thermal stability under operating conditions, e.g. for an automotive up to 873 K, needs to be guaranteed. For the first time, the long-term stability of n- and p-type HH materials is proved. We investigated HH materials based on the Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a maximum Seebeck coefficient of S around 210 muV/K and an intrinsic phase separation into two HH phases. The dendritic microstructure is temperature resistant and maintained the low thermal conductivity values (kappa less than 4 W/Km). Our results emphasize that phase-separated HH compounds are suitable low cost materials and can lead to enhanced thermoelectric efficiencies beyond the set benchmark for industrial applications.",1502.01828v1 2015-06-11,Magnetism in tetragonal manganese-rich Heusler compounds,"A comprehensive study of the total energy of manganese-rich Heusler compounds using density functional theory is presented. Starting from a large set of cubic parent systems, the response to tetragonal distortions is studied in detail. We single out the systems that remain cubic from those that most likely become tetragonal. The driving force of the tetragonal distortion and its effect on the magnetic properties, especially where they deviate from the Slater--Pauling rule, as well as the trends in the Curie temperatures, are highlighted. By means of partial densities of states, the electronic structural changes reveal the microscopic origin of the observed trends. We focus our attention on the magnetocrystalline anisotropy and find astonishingly high values for tetragonal Heusler compounds containing heavy transition metals accompanied by low magnetic moments, which indicates that these materials are promising candidates for spin-transfer torque magnetization-switching applications.",1506.03735v1 2015-07-30,"First principle investigations of the structural, electronic and magnetic properties of the new zirconium based full-Heusler compounds, Zr2MnZ (Z = Al, Ga and In)","The crystal structure, electronic and magnetic properties of the new full-Heusler compounds Zr2MnZ (Z=Al, Ga, In), were studied within the Density Functional Theory (DFT) framework. The materials exhibit unique properties that connect the spin gapless semiconducting character with the completely compensated ferrimagnetism. In magnetic configurations, Zr2MnZ (Z=Al, Ga, In) crystallize in inverse Heusler structure, are stable against decomposition and have zero magnetic moment per formula unit properties, in agreement with Slater-Pauling rule. The Zr2MnAl compound presents spin gapless semiconducting properties with a energy band gap of 0.41 eV in the majority spin channel and a zero band gap in the minority spin channel. By substituting Ga or In elements, for Al in Zr2MnAl, semiconducting pseudo band gaps are formed in the majority spin channels due to the different neighborhood around the manganese atoms, which decreases the energy of Mn's triple degenerated anti-bonding states.",1507.08605v2 2015-11-10,Large low-field positive magnetoresistance in nonmagnetic half-Heusler ScPtBi single crystal,"High-quality nonmagnetic half-Heusler ScPtBi single crystals were synthesized by a Bi self-flux method. This compound was revealed to be a hole-dominated semimetal with a large low-field magnetoresistance up to 240% at 2K in a magnetic field of 1T. Magneto-transport measurements demonstrated that the large low-field magnetoresistance effect resulted from the coexistence of field-induced metal-semiconductor transition and weak-antilocalization effect. Moreover, Hall measurements indicated that ScPtBi single crystal showed a high mobility over a wide temperature region even up to room temperature (4050 cm2V-1s-1 at 2K - 2016 cm2V-1s-1 at 300K). These findings not only suggest the nonmagnetic ScPtBi semimetal a potential material candidate for applications in high-sensitivity magnetic sensors, but also are of great significance to comprehensively understand the rare-earth based half-Heusler compounds.",1511.03017v1 2016-01-28,LaPtSb: a half-Heusler compound with high thermoelectric performance,"The electronic and transport properties of the half-Heusler compound LaPtSb are investigated by performing first-principles calculations combined with semi-classical Boltzmann theory and deformation potential theory. Compared with many typical half-Heusler compounds, the LaPtSb exhibits obviously larger power factor at room temperature, especially for the n-type system. Together with the very low lattice thermal conductivity, the thermoelectric figure of merit (ZT) of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the carrier concentration.",1601.07690v4 2016-04-13,Ultralow Thermal Conductivity in Full-Heusler Semiconductors,"Semiconducting half- and, to a lesser extent, full-Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full-Heusler compounds with ten valence electrons ($X_2YZ$, $X$=Ca, Sr, and Ba; $Y$= Au and Hg; $Z$=Sn, Pb, As, Sb, and Bi) through high-throughput $ab-initio$ screening. These new compounds exhibit ultralow lattice thermal conductivity $\kappa_{\text{L}}$ close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials.",1604.03827v2 2016-04-18,"Itinerant G-type antiferromagnetism in D0$_3$-type V$_3$Z (Z=Al, Ga, In) compounds: A first-principles study","Heusler compounds are widely studied due to their variety of magnetic properties making them ideal candidates for spintronic and magnetoelectronic applications. V$_3$Al in its metastable D0$_3$-type Heusler structure is a prototype for a rare antiferromagnetic gapless behavior. We provide an extensive study on the electronic and magnetic properties of V$_3$Al, V$_3$Ga and V$_3$In compounds based on state-of-the-art electronic structure calculations. We show that the ground state for all three is a G-type itinerant antiferromagnetic gapless semiconductor. The large antiferromagnetic exchange interactions lead to very high N\'eel temperatures, which are predicted to be around 1000 K. The coexistence of the gapless and antiferromagnetic behaviors in these compounds can be explained considering the simultaneous presence of three V atoms at the unit cell using arguments which have been employed for usual inverse Heusler compounds. We expect that our study on these compounds to enhance further the interest on them towards the optimization of their growth conditions and their eventual incorporation in devices.",1604.05137v1 2017-07-10,Inflated nodes and surface states in superconducting half-Heusler compounds,"Two topics of high current interest in the field of unconventional superconductivity are non-centrosymmetric superconductors and multiband superconductivity. Half-Heusler superconductors such as YPtBi exemplify both. In this paper, we study bulk and surface states in nodal superconducting phases of the half-Heusler compounds, belonging to the $A_1$ ($s+p$-like) and $T_2$ ($k_zk_x+ik_zk_y$-like) irreducible representations of the point group. These two phases preserve and break time-reversal symmetry, respectively. For the $A_1$ case, we find that flat surface bands persist in the multiband system. In addition, the system has dispersive surface bands with zero-energy crossings forming Fermi arcs, which are protected by mirror symmetries. For the $T_2$ case, there is an interesting coexistence of point and line nodes, known from the single-band case, with Bogoliubov Fermi surfaces (two-dimensional nodes). There are no flat-band surface states, as expected, but dispersive surface bands with Fermi arcs exist. If these arcs do not lie in high-symmetry planes, they are split by the antisymmetric spin-orbit coupling so that their number is doubled compared to the inversion-symmetric case.",1707.02739v2 2018-01-31,Unconventional superconductivity and Surface pairing symmetry in Half-Heusler Compounds,"Signatures of nodal line/point superconductivity have been observed in half-Heusler compounds, such as LnPtBi (Ln = Y, Lu). Topologically non-trivial band structures, as well as topological surface states, has also been confirmed by angular-resolved photoemission spectroscopy in these compounds. In this work, we present a systematical classification of possible gap functions of bulk states and surface states in half-Heusler compounds and the corresponding topological properties based on the representations of crystalline symmetry group. Different from all the previous studies based on four band Luttinger model, our study starts with the six-band Kane model, which involves both four p-orbital type of {\Gamma}8 bands and two s-orbital type of {\Gamma}6 bands. Although the {\Gamma}6 bands are away from the Fermi energy, our results reveal the importance of topological surface states, which originate from the band inversion between {\Gamma}6 and {\Gamma}8 bands, in determining surface properties of these compounds in the superconducting regime by combining topological bulk state picture and non-trivial surface state picture.",1801.10286v1 2018-03-27,Subamorphous thermal conductivity of crystalline half-Heusler superlattices,"The quest to improve the thermoelectric figure of merit has mainly followed the roadmap of lowering the thermal conductivity while keeping unaltered the power factor of the material. Ideally an electron-crystal phonon-glass system is desired. In this work, we report an extraordinary reduction of the cross-plane thermal conductivity in crystalline (TiNiSn):(HfNiSn) half-Heusler superlattices. We create SLs with thermal conductivities below the effective amorphous limit, which is kept in a large temperature range (120-300 K). We measured thermal conductivity at room temperature values as low as 0.75 W/(m K), the lowest thermal conductivity value reported so far for half-Heusler compounds. By changing the deposition conditions, we also demonstrate that the thermal conductivity is highly impacted by the way the single segments of the superlattice grow. These findings show a huge potential for thermoelectric generators where an extraordinary reduction of the thermal conductivity is required but without losing the crystal quality of the system.",1803.09920v2 2020-01-20,Ab initio design of quaternary Heusler compounds for reconfigurable magnetic tunnel diodes and transistors,"Reconfigurable magnetic tunnel diodes and transistors are a new concept in spintronics. The realization of such a device requires the use of materials with unique spin-dependent electronic properties such as half-metallic magnets (HMMs) and spin-gapless semiconductors (SGSs). Quaternary Heusler compounds offer a unique platform to design within the same family of compounds HMMs and SGSs with similar lattice constants to make coherent growth of the consecutive spacers of the device possible. Employing state-of-the-art first-principles calculations, we scan the quaternary Heusler compounds and identify suitable candidates for these spintronic devices combining the desirable properties: (i) HMMs with sizable energy gap or SGSs with spin gaps both below and above the Fermi level, (ii) high Curie temperature, (iii) convex hull energy distance less than 0.20 eV, and (iv) negative formation energies. Our results pave the way for the experimental realization of the proposed magnetic tunnel diodes and transistors.",2001.07029v1 2017-04-04,Model Hamiltonian and Time Reversal Breaking Topological Phases of Anti-ferromagnetic Half-Heusler Materials,"In this work, we construct a generalized Kane model with a new coupling term between itinerant electron spins and local magnetic moments of anti-ferromagnetic ordering in order to describe the low energy effective physics in a large family of anti-ferromagnetic half-Heusler materials. Topological properties of this generalized Kane model is studied and a large variety of topological phases, including Dirac semimetal phase, Weyl semimetal phase, nodal line semimetal phase, type-B triple point semimetal phase, topological mirror (or glide) insulating phase and anti-ferromagnetic topological insulating phase, are identified in different parameter regions of our effective models. In particular, we find that the system is always driven into the anti-ferromagnetic topological insulator phase once a bulk band gap is open, irrespective of the magnetic moment direction, thus providing a robust realization of anti-ferromagentic topological insulators. Furthermore, we discuss the possible realization of these topological phases in realistic anti-ferromagnetic half-Heusler materials. Our effective model provides a basis for the future study of physical phenomena in this class of materials.",1704.01138v1 2019-01-27,Computational search for ultrasmall and fast skyrmions in the Inverse Heusler family,"Skyrmions are magnetic excitations that are potentially ultrasmall and topologically protected, making them interesting for high-density all-electronic ultrafast storage applications. While recent experiments have confirmed the existence of various types of skyrmions, their typical sizes are much larger than traditional domain walls, except at very low temperature. In this work, we explore the optimal material parameters for hosting ultra-small, fast, and room temperature stable skyrmions. As concrete examples, we explore potential candidates from the inverse Heusler family. Using first-principles calculations of structural and magnetic properties, we identify several promising ferrimagnetic inverse Heusler half-metal/near half-metals and analyze their phase space for size and metastability.",1901.09446v1 2019-01-28,Magnetotransport properties and giant anomalous Hall angle in half-Heusler compound TbPtBi,"Magnetic lanthanide half-Heuslers ($R$PtBi; $R$ being the lanthanide) represent an attractive subgroup of the Heusler family and have been identified as ideal candidates for time reversal symmetry breaking topological Weyl semimetals. In this paper, we present the detailed analysis of the magnetotransport properties of frustrated antiferromagnet TbPtBi. This material shows large, non-saturating magnetoresistance (MR) with unusual magnetic field dependence. The MR of TbPtBi is significantly anisotropic with respect to the magnetic field, applied along different crystallographic directions and indicates the anisotropic nature of the Fermi surface. The chiral anomaly induced negative longitudinal magnetoresistance confirms the presence of Weyl fermions. At low temperature, Berry phase driven large anomalous Hall conductivity has been observed. The calculated anomalous Hall angle is the largest reported so far.",1901.09534v1 2012-09-27,Fabrication and characterization of semiconducting half Heusler YPtSb thin films,"The semiconducting half Heusler compound YPtSb was predicted theoretically to be capable of changing into topological insulator under proper strain. In this work, p type semiconducting half-Heusler YPtSb thin films were prepared by magnetron co-sputtering method from a specially designed target for the first time. Textured structure with (111) plane paralleling with (001) of MgO substrate was observed when YPtSb thin films were grown on MgO (100) substrate at 600{\deg}C.Electrical measurements show that the resistivity of YPtSb films decreases with increasing temperature, indicating a semiconductor-like behavior. The carrier density is as high as 1.15 X 10^21 cm-3 at 300 K. The band gap of YPtSb thin films obtained by infrared spectroscopy is around 0.1 - 0.15 eV, which is well in agreement with the theoretical prediction and the value measured in bulk YPtSb.",1209.6288v2 2020-04-26,High thermoelectric performance of half-Heusler compound BiBaK with intrinsically low lattice thermal conductivity,"Half-Heusler compounds usually exhibit relatively higher lattice thermal conductivity that is undesirable for thermoelectric applications. Here we demonstrate by first-principles calculations and Boltzmann transport theory that the BiBaK system is an exception, which has rather low thermal conductivity as evidenced by very small phonon group velocity and relaxation time. Detailed analysis indicates that the heavy Bi and Ba atoms form a cage-like structure, inside which the light K atom rattles with larger atomic displacement parameters. In combination with its good electronic transport properties, the BiBaK shows a maximum n-type ZT value of 1.9 at 900 K, which outperforms most half-Heusler thermoelectric materials.",2004.12324v1 2020-08-11,"Anomalous Hall effect in half-metallic Heusler compound Co$_{2}$Ti$X$ ($X$=Si, Ge)","Though Weyl fermions have recently been observed in several materials with broken inversion symmetry, there are very few examples of such systems with broken time reversal symmetry. Various Co$_{2}$-based half-metallic ferromagnetic Heusler compounds are lately predicted to host Weyl type excitations in their band structure. These magnetic Heusler compounds with broken time reversal symmetry are expected to show a large momentum space Berry curvature, which introduces several exotic magneto-transport properties. In this report, we present systematic analysis of experimental results on anomalous Hall effect (AHE) in Co$_2$Ti$X$ ($X$=Si and Ge). This study is an attempt to understand the role of Berry curvature on AHE in Co$_2$Ti$X$ family of materials. The anomalous Hall resistivity is observed to scale quadratically with the longitudinal resistivity for both the compounds. The detailed analysis indicates that in anomalous Hall conductivity, the intrinsic Karplus-Luttinger Berry phase mechanism dominates over the extrinsic skew scattering and side-jump mechanism.",2008.04837v1 2020-08-17,Interaction between skyrmions and antiskyrmions in a coexisting phase of a Heusler material,"Coexisting phases of magnetic skyrmions and antiskyrmions have proposed to exhibit a variety of fascinating properties, owing to interactions between them. The recent discovery of the coexisting phase in a Heusler material could offer a platform for skyrmion-antiskyrmion-based spintronics. Here we report Lorentz electron microscopy experiments and micromagnetic simulations in a similar Heusler material, Mn$_{1.3}$Pt$_{1.0}$Pd$_{0.1}$Sn. Around $B_c \sim$ 420$\,$mT, we find a stochastic reversible transformation and a room temperature coexisting phase of elliptical skyrmions and square-shaped antiskyrmions. The closeness of the energy competition is sensitive to the exchange stiffness constants and sample thickness. Furthermore, we reveal isotropic long-range repulsive interaction between the skyrmions and antiskyrmions regardless of their shapes and the skyrmion helicities, in stark contrast to conventional thought of angle- and helicity-dependent short-range pairwise interactions. The observed interaction possibly results from the topological protection against the intrusion of magnetic flux density coming from skyrmions (antiskyrmions) into antiskyrmions (skyrmions). Our results provide new insight into interacting skyrmions and antiskyrmions and a guide for developing skyrmion-antiskyrmion-based spintronics.",2008.07272v2 2020-08-31,Giant magnetocaloric effect driven by first-order magneto-structural transition in cosubstituted Ni-Mn-Sb Heusler compounds: predictions from \textit{Ab initio} and Monte Carlo calculations,"Using Density Functional Theory and a thermodynamic model [Physical Review B 86, 134418 (2012)], in this paper, we provide an approach to systematically screen compounds of a given Heusler family to predict ones that can yield giant magnetocaloric effect driven by a first-order magneto-structural transition. We apply this approach to two Heusler series Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at Ni and Mn sites. We predict four new compounds with potentials to achieve the target properties. Our computations of the thermodynamic parameters, relevant for magnetocaloric applications, show that the improvement in the parameters in the predicted cosubstituted compounds can be as large as four times in comparison to the off-stoichiometric Ni-Mn-Sb and a compound derived by single substitution at the Ni site, where magnetocaloric effects have been observed experimentally. This work establishes a protocol to select new compounds that can exhibit large magnetocaloric effects and demonstrate cosubstitution as a route for more flexible tuneability to achieve outcomes, better than the existing ones.",2008.13479v1 2016-03-10,Pairing of j=3/2 fermions in half-Heusler superconductors,"We theoretically consider the superconductivity of the topological half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between j=3/2 fermion states, which leads to qualitative differences from the conventional theory of pairing between j=1/2 states. In particular, this permits Cooper pairs with quintet or septet total angular momentum, in addition to the usual singlet and triplet states. Purely on-site interactions can generate s-wave quintet time-reversal symmetry-breaking states with topologically nontrivial point or line nodes. These local s-wave quintet pairs reveal themselves as d-wave states in momentum space. Furthermore, due to the broken inversion symmetry in these materials, the s-wave singlet state can mix with a p-wave septet state, again with topologically-stable line nodes. Our analysis lays the foundation for understanding the unconventional superconductivity of the half-Heuslers.",1603.03376v3 2016-03-27,Thermoelectric properties of half-Heusler $\mathrm{ZrNiPb}$ by using first principles calculations,"We investigate electronic structures and thermoelectric properties of recent synthetic half-Heusler $\mathrm{ZrNiPb}$ by using generalized gradient approximation (GGA) and GGA plus spin-orbit coupling (GGA+SOC). Calculated results show that $\mathrm{ZrNiPb}$ is a indirect-gap semiconductor. Within the constant scattering time approximation, semi-classic transport coefficients are performed through solving Boltzmann transport equations. It is found that the SOC has more obvious influence on power factor in p-type doping than in n-type doping, leading to a detrimental effect in p-type doping. These can be explained by considering the SOC influences on the valence bands and conduction bands near the Fermi level. The lattice thermal conductivity as a function of temperature is calculated, and the corresponding lattice thermal conductivity is 14.5 $\mathrm{W m^{-1} K^{-1}}$ at room temperature. By comparing the experimental transport coefficients with calculated ones, the scattering time is attained for 0.333 $\times$ $10^{-14}$ s. Finally, the thermoelectric figure of merit $ZT$ can be attained, and the $ZT$ value can be as high as 0.30 at high temperature by choosing appropriate doping level. It is possible to reduce lattice thermal conductivity by point defects and boundaries, and make half-Heusler $\mathrm{ZrNiPb}$ become potential candidate for efficient thermoelectricity.",1603.08203v1 2016-12-19,Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compound Mn1.5FeV0.5Al,"The Slater-Pauling rule states that L21 Heusler compounds with 24 valence electrons do never exhibit a total spin magnetic moment. In case of strongly localized magnetic moments at one of the atoms (here Mn) they will exhibit a fully compensated half-metallic ferrimagnetic state instead, in particular, when symmetry does not allow for antiferromagnetic order. With aid of magnetic and anomalous Hall effect measurements it is experimentally demonstrated that Mn1.5V0.5FeAl follows such a scenario. The ferrimagnetic state is tuned by the composition. A small residual magnetization, that arises due to a slight mismatch of the magnetic moments in the different sublattices results in a pronounced change of the temperature dependence of the ferrimagnet. A compensation point is confirmed by observation of magnetic reversal and sign change of the anomalous Hall effect. Theoretical models are presented that correlate the electronic structure and the compensation mechanisms of the different half-metallic ferrimagnetic states in the Mn-V-Fe-Al Heusler system.",1612.06300v1 2017-06-01,Prediction of triple point fermions in simple half-Heusler topological insulators,"We predict the existence of triple point fermions in the band structure of several half-Heusler topological insulators by $ab~initio$ calculations and the Kane model. We find that many half-Heusler compounds exhibit multiple triple points along four independent $C_3$ axes, through which the doubly degenerate conduction bands and the nondegenerate valence band cross each other linearly nearby the Fermi energy. When projected from the bulk to the (111) surface, most of these triple points are located far away from the surface $\bar{\Gamma}$ point, as distinct from previously reported triple point fermion candidates. These isolated triple points give rise to Fermi arcs on the surface, that can be readily detected by photoemission spectroscopy or scanning tunneling spectroscopy.",1706.00200v1 2020-06-09,Detection of antiskyrmions by topological Hall effect in Heusler compounds,"Heusler compounds having $\textit{D}$${}_{2d}$ crystal symmetry gained much attention recently due to the stabilization of a vortex-like spin texture called antiskyrmions in thin lamellae of Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn as reported in the work of Nayak $\textit{et al.}$ [Nature (London) 548, 561 (2017)]. Here we show that bulk Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn undergoes a spin-reorientation transition from a collinear ferromagnetic to a noncollinear configuration of Mn moments below 135 K, which is accompanied by the emergence of a topological Hall effect. We tune the topological Hall effect in Pd and Rh substituted Mn${}_{1.4}$PtSn Heusler compounds by changing the intrinsic magnetic properties and spin textures. A unique feature of the present system is the observation of a zero-field topological Hall resistivity with a sign change which indicates the robust formation of antiskyrmions.",2006.05190v1 2020-10-22,Anomalous Quantum Oscillations in Spin-3/2 Topological Semimetal YPtBi,"The proposed high-spin superconductivity in the half-Heusler compounds changes the landscape of superconductivity research. While superconducting instability is possible only in systems with quantum mechanically coherent quasiparticles, it has not been verified for any proposed high-spin Fermi surfaces. Here we report an observation of anomalous Shubnikov-de Haas effect in half-Heusler YPtBi, which is compatible with a coherent $j=3/2$ Fermi surface. The quantum oscillation (QO) signal in cubic YPtBi manifests extreme anisotropy upon rotation of the magnetic field from [100] to [110] crystallographic direction where the QO signal drastically vanishes near [110]. This radical anisotropy for a cubic system cannot be explained by trivial scenarios for QO involving effective mass or impurity scattering, but it is naturally explained by the warping feature of the $j=3/2$ Fermi surface YPtBi. Our results prove the high-spin nature of the quasiparticle in the half-Heusler compounds, which makes the realization of the unprecedented high-spin superconductivity more plausible.",2010.12085v2 2020-11-12,Anomalous Hall effect and negative longitudinal magnetoresistance in half-Heusler topological semimetal candidates TbPtBi and HoPtBi,"Half-Heusler compounds have attracted significant attention because of their topologically non-trivial electronic structure, which leads to unusual electron transport properties. We thoroughly investigated the magnetotransport properties of high-quality single crystals of two half-Heusler phases, TbPtBi and HoPtBi, in pursuit of the characteristic features of topologically non-trivial electronic states. Both studied compounds are characterized by the giant values of transverse magnetoresistance with no sign of saturation in magnetic field up to 14 T. HoPtBi demonstrates the Shubnikov-de Haas effect with two principal frequencies, indicating a complex Fermi surface; the extracted values of carrier effective masses are rather small, $0.18\,m_e$ and $0.27\,m_e$. The investigated compounds exhibit negative longitudinal magnetoresistance and anomalous Hall effect, which likely arise from a nonzero Berry curvature. Both compounds show strongly anisotropic magnetoresistance, that in HoPtBi exhibits a butterfly-like behavior.",2011.06290v1 2021-04-22,Chemical bonding origin of the thermoelectric power factor in Half-Heusler semiconductors,"Intermetallic semiconductors with the cubic Half-Heusler structure (XYZ) have excellent thermoelectric properties. This has been attributed to the high degeneracy of the carrier pockets in the band structure, but large differences are found between different material compositions. Half-Heuslers are often interpreted within Zintl chemistry, making a clear distinction between an electropositive cation ($X^{n+}$) and an extended polyanion ($YZ^{n-}$). Based on quantitative real space chemical bonding analysis, we unravel large degrees of covalent bonding between the formal cation and anion, making the Zintl distinction clearly invalid. This covalence is shown to strongly affect the band structure, thermoelectric properties and response properties in the materials, with improved thermoelectric properties observed for those materials that least follow the Zintl concept. This expands our knowledge of the chemical bonding motifs governing physical properties, and gives a critical view on the simplistic chemical concepts too often applied for design of complex materials.",2104.11281v1 2021-04-29,Nonlinear Hall Effect in Antiferromagnetic Half-Heusler Materials,"It has recently been demonstrated that various topological states, including Dirac, Weyl, nodal-line, and triple-point semimetal phases, can emerge in antiferromagnetic (AFM) half-Heusler compounds. However, how to determine the AFM structure and to distinguish different topological phases from transport behaviors remains unknown. We show that, due to the presence of combined time-reversal and fractional translation symmetry, the recently proposed second-order nonlinear Hall effect can be used to characterize different topological phases with various AFM configurations. Guided by the symmetry analysis, we obtain the expressions of the Berry curvature dipole for different AFM configurations. Based on the effective model, we explicitly calculate the Berry curvature dipole, which is found to be vanishingly small for the triple-point semimetal phase, and large in the Weyl semimetal phase. Our results not only put forward an effective method for the identification of magnetic orders and topological phases in AFM half-Heusler materials, but also suggest these materials as a versatile platform for engineering the non-linear Hall effect.",2104.14127v1 2022-01-08,Atomic disorder and Berry phase driven anomalous Hall effect in Co2FeAl Heusler compound,"Co2-based Heusler compounds are the promising materials for the spintronics application due to their high Curie temperature, large spin-polarization, large magnetization density, and exotic transport properties. In the present manuscript, we report the anomalous Hall effect (AHE) in a polycrystalline Co2FeAl Heusler compound using combined experimental and theoretical studies. The Rietveld analysis of high-resolution synchrotron x-ray diffraction data reveals a large degree (~50 %) of antisite disorder between Fe and Al atoms. The analysis of anomalous transport data provides the experimental anomalous Hall conductivity (AHC) about 227 S/cm at 2 K with an intrinsic contribution of 155 S/cm, which has nearly constant variation with temperature. The detailed scaling analysis of anomalous Hall resistivity suggests that the AHE in Co2FeAl is governed by the Berry phase driven intrinsic mechanism. Our theoretical calculations reveal that the disorder present in Co2FeAl compound enhances the Berry curvature induced intrinsic AHC.",2201.02864v1 2022-07-15,Band splitting induced Berry flux and intrinsic anomalous Hall conductivity in NiCoMnGa quaternary Heusler compound,"The anomalous transport properties of Heusler compounds become a hotspot of research in recent years due to their unique band structure and possible application in spintronics. In this paper, we report the anomalous Hall effect in polycrystalline NiCoMnGa quaternary Heusler compound by experimental means and theoretical calculations. The experimental anomalous Hall conductivity (AHC) was found at about 256 S/cm at 10K with an intrinsic contribution of ~ 121 S/cm. The analysis of Hall data reveals the presence of both extrinsic and intrinsic contributions in AHE. Our theoretical calculations show that a pair of spin-orbit coupled band formed by the band splitting due to spin-orbit interaction (SOI) at the Fermi level produces a finite Berry flux in the system that provides the intrinsic AHC about 100 S/cm, which is in good agreement with the experiment.",2207.07313v1 2022-08-04,"Ab-initio study of stable 3d, 4d and 5d transition metal based Quaternary Heusler compounds","The realization of the stable structure of Heusler compounds and the study of different properties is an important step for their potential application in spintronics and magnetoelectronic devices. In this paper, using the plane-wave pseudopotential method within the framework of density functional theory (DFT), we investigate 25 Quaternary Heusler compounds for their electronic, magnetic, and mechanical properties. The Open Quantum Materials Database (OQMD) is used to screen a large number of compounds to narrow down the possible synthesizable materials. The convex-hull distance and elastic constants are exploited to confirm the thermodynamic and mechanical stability of the compounds. The careful study of the different structures suggests that 5 of the compounds crystallize in type-1 structure whereas 20 compounds adopt type-3 structure. The possible explanation for the observed behavior is made by invoking electronegativity arguments and through the study of individual spin magnetic moments in different structures. The compounds with diverse electronic and magnetic properties such as half-metallicity, spin gapless semiconducting behavior, and non-magnetic semi-conducting property have been identified.",2208.02401v2 2024-03-01,Spin-gapped metals: A novel class of materials -- the case of semi-Heusler compounds,"Gapped metals, a recently discovered new class of materials, possess a band gap slightly above or below the Fermi level. These materials are intrinsic p- or n-type semiconductors eliminating the need for extrinsic doping. Inspired by this concept, we propose the so-called ""spin-gapped metals"" exhibiting intrinsic p- or n-type behavior for each spin channel independently. Their properties would be similar to the dilute magnetic semiconductors eliminating the requirement for transition metal doping. Here, we demonstrate this novel concept in semi-Heusler compounds using first principles electronic band structure calculations. We comprehensively analyze their electronic and magnetic properties, paving the way for novel technological applications of Heusler compounds.",2403.00936v1 2002-12-17,Charge Distributions in Metallic Alloys: a Charge Excess Functional theory approach,"Charge Distributions in Metallic Alloys: a Charge Excess Functional theory approach",0212398v1 2009-03-08,Alloy Stabilized Wurtzite Ground State Structures of Zinc-Blende Semiconducting Compounds,"The ground state structures of the A$_x$B$_{1-x}$C wurtzite (WZ) alloys with $x=$0.25, 0.5, and 0.75 are revealed by a ground state search using the valence-force field model and density-functional theory total energy calculations. It is shown that the ground state WZ alloy always has a lower strain energy and formation enthalpy than the corresponding zinc-blende (ZB) alloy. Therefore, we propose that the WZ phase can be stabilized through alloying. This novel idea is supported by the fact that the WZ AlP$_{0.5}$Sb$_{0.5}$, AlP$_{0.75}$Sb$_{0.25}$, ZnS$_{0.5}$Te$_{0.5}$, and ZnS$_{0.75}$Te$_{0.25}$ alloys in the lowest energy structures are more stable than the corresponding ZB alloys. To our best knowledge, this is the first example where the alloy adopts a structure distinct from both parent phases.",0903.1449v1 2014-04-18,Mn$_m$Tc$_n$ nanoalloy clusters obey Vegard's law : A first principles prediction,"With a view to gain an understanding about the alloying tendency of bimetallic nano alloy clusters of isoelectronics constituents, we studied the structural and mixing behaviors of Mn$_m$Tc$_n$ alloy clusters with $m+n =$13 for all possible compositions, using first principles electronic structure calculations. Our study reports a favorable mixing tendency for the alloy clusters. The average bond lengths of the minimum energy structures show an overall linear variation with concentrations, indicating a Vegard's law like variation for the nano alloy clusters, though the optimized structures undergo a structural transition from a closed and compact structure for the Mn-rich alloy clusters to an open layered like structure for the Tc-rich alloy clusters. We figure out a continuous and smooth interplay between hybridization and magnetization properties of the alloy clusters, which plays a vital role for the Vegard's law like variation in their average bond lengths.",1404.4703v1 2014-07-01,Electronic band structure and ambipolar electrical properties of Cu2O based semiconductor alloys,"Tuning the opto-electronic properties through alloying is essential for semiconductor technology. Currently, mostly isovalent and isostructural alloys are used (e.g., group-IV and III-V), but a vast and unexplored space of novel functional materials is conceivable when considering more complex alloys by mixing aliovalent and heterostructural constituents. The real challenge lies in the quantitative property prediction for such complex alloys to guide their experimental exploration. We developed an approach to predict compositional dependence of both band-structure and electrical properties from ab-initio calculations by extending conventional dilute defect model to higher (alloy) concentrations. Considering alloying of aliovalent (Mg, Zn, Cd) cations and isovalent anions (S, Se) into Cu2O, we predict tunability of band-gap energies and doping levels over a wide range, including the type conversion from p- to n-type. Initial synthesis and characterization of Zn and Se substituted Cu2O support the defect model, suggesting these alloys as promising novel oxide semiconductor materials.",1407.0101v1 2021-07-01,Elastic energy of multi-component solid solutions and strain origins of phase stability in high-entropy alloys,"The elastic energy of mixing for multi-component solid solutions is derived by generalizing Eshelby's sphere-in-hole model for binary alloys. By surveying the dependence of the elastic energy on chemical composition and lattice misfit, we propose a lattice strain coefficient {\lambda}*. Applying to several high-entropy alloys and superalloys, we found that most solid solution alloys are stable when {\lambda}*<0.16, analogous to the Hume-Rothery atomic-size rule for binary alloys. We also reveal that the polydispersity index {\delta}, frequently used for describing strain in multi-component alloys, is directly related to the elastic energy (e) with e=q{\delta}^2, q being an elastic constant. Furthermore, the effects of (i) the number and (ii) the atomic-size distribution of constituting elements on the phase stability of high-entropy alloys were quantified. The present derivations open for richer considerations of elastic effects in high-entropy alloys, offering immediate support for quantitative assessments of their thermodynamic properties and studying related strengthening mechanisms.",2107.00514v1 2019-04-09,Alloy Design for Mechanical Properties: Conquering the Length Scales,"Predicting the structural response of advanced multiphase alloys and understanding the underlying microscopic mechanisms that are responsible for it are two critically important roles modeling plays in alloy development. An alloys demonstration of superior properties, such as high strength, creep resistance, high ductility, and fracture toughness, is not sufficient to secure its use in widespread application. Still, a good model is needed, to take measurable alloy properties, such as microstructure and chemical composition, and forecast how the alloy will perform in specified mechanical deformation conditions, including temperature, time, and rate. In this bulletin, we highlight recent achievements by multiscale modeling in elucidating the coupled effects of alloying, microstructure, and the dynamics of mechanisms on the mechanical properties of polycrystalline alloys. Much of the understanding gained by these efforts relied on integration of computational tools that varied over many length and time scales, from first principles density functional theory, atomistic simulation methods, dislocation and defect theory, micromechanics, phase field modeling, single crystal plasticity, and polycrystalline plasticity.",1904.04569v1 2018-12-05,Influence of composition and heating schedules on compatibility of FeCrAl alloys with high-temperature steam,"FeCrAl alloys are proposed and being intensively investigated as alternative accident tolerant fuel (ATF) cladding for nuclear fission application. Herein, the influence of major alloy elements (Cr and Al), reactive element effect and heating schedules on the oxidation behavior of FeCrAl alloys in steam up to 1500{\deg}C was examined. In case of transient ramp tests, catastrophic oxidation, i.e. rapid and complete consumption of the alloy, occurred during temperature ramp up to above 1200{\deg}C for specific alloys. The maximum compatible temperature of FeCrAl alloys in steam increases with raising Cr and Al content, decreasing heating rates during ramp period and doping of yttrium. Isothermal oxidation resulted in catastrophic oxidation at 1400{\deg}C for all examined alloys. However, formation of a protective alumina scale at 1500{\deg}C was ascertained despite partial melting. The occurrence of catastrophic oxidation seems to be controlled by dynamic competitive mechanisms between mass transfer of Al from the substrate and transport of oxidizing gas through the scale both toward the metal/oxide scale interface.",1812.01850v1 2020-04-14,Nanoporous AuPt and AuPtAg alloy co-catalysts formed by dewetting-dealloying on ordered TiO2 nanotube surface lead to significantly enhanced photocatalytic H2 generation,"Effective co-catalysts are of key importance for photocatalytic H2 generation from aqueous environments. An attractive co-catalyst candidate are AuPt (metastable) alloys due to the synergistic electronic and chemical interaction of the constituents in the charge transfer and H2 evolution process. Here we introduce the fabrication of AuPt alloy nanoparticles with nanoporosity (pore size of 2-5 nm) fabricated on spaced TiO2 nanotubes. By dewetting a layered AgAuPt coating, we form AuPtAg alloy nanoparticles. From these alloys, Ag can selectively be dissolved leading to the desired nanoporous AuPt alloy particles with diameter in the range of 10-70 nm deposited as a gradient on the TiO2 nanotubes. A significant enhancement of photocatalytic H2 generation is obtained compared to the same loading of monometallic or nonporous alloy. The nanoporous AuPt particles provide not only a large surface area to volume ratio (and are thus more effective) but also show the intrinsic synergy of a AuPt alloy for H2 generation.",2005.01486v1 2022-03-18,Designing a thermodynamically stable and intrinsically ductile refractory alloy,"Developing ductile refractory BCC alloys has remained a challenge. The intrinsic ductility (D) of an alloy is the ratio of surface energy ($\gamma_s$) and unstable stacking fault energy ($\gamma_{usfe}$). Lowering the valence electron concentration has been shown to improve the intrinsic ductility of refractory alloys. However, Re has been widely used to ductilize W, contrary to the low valency criteria suggested in the literature. Here we use density functional theory to calculate the enthalpy of formation, $\gamma_{usfe}$ and $\gamma_s$ of Group IV, V, VI elements and their 25 equiatomic binary alloys in BCC crystal structure. We found that positive enthalpy leads to a considerable reduction in $\gamma_{usfe}$ compared to composition averaged value, resulting in improved intrinsic ductility. Enthalpy is maximum at the equiatomic concentrations indicating the highly repulsive interaction between the alloy constituents and vicer-versa. We found that the repulsive interaction between the alloy constituents leads to a reduction in $\gamma_{usfe}$, making alloys intrinsically ductile.",2203.09949v3 2016-03-11,Mechanocaloric effects in Shape Memory Alloys,"Shape memory alloys are a class of ferroic materials which undergo a structural (martensitic) transition where the associated ferroic property is a lattice distortion (strain). The sensitiveness of the transition to the conjugated external field (stress), together with the latent heat of the transition gives rise to giant mechanocaloric effects. In non-magnetic shape memory alloys, the lattice distortion is mostly described by a pure shear and the martensitic transition in this family of alloys is strongly affected by uniaxial stress whereas it is basically insensitive to hydrostatic pressure. As a result, non-magnetic alloys exhibit giant elastocaloric effects but negligible barocaloric effects. By contrast, in a number of magnetic shape memory alloys, the lattice distortion at the martensitic transition involves a volume change in addition to the shear strain. Those alloys are affected by both uniaxial stress and hydrostatic pressure and they exhibit giant elastocaloric and barocaloric effects. The paper aims at providing a critical survey of available experimental data on elastocaloric and barocaloric effects in magnetic and non-magnetic shape memory alloys.",1603.03658v1 2017-02-09,"First-principles high-throughput screening of shape-memory alloys based on energetic, dynamical, and structural properties","First-principles-based materials screening is systematically performed to discover new combinations of chemical elements possibly making shape-memory alloys (SMAs). The B2, D03, and L21 crystal structures are considered as the parent phases, and the 2H and 6M structures are considered as the martensitic phases. 3,384 binary and 3,243 ternary alloys (6,627 in total) with stoichiometric composition ratios are investigated by the materials screening in terms of energetic and dynamical stabilities of the martensitic phases as well as structural compatibility between the parent and the martensitic phases. 187 alloys are found to survive after the screening. Some of the surviving alloys are constituted by the chemical elements already widely used in SMAs, but other various metallic elements are also found in the surviving alloys. The energetic stability of the surviving alloys is further analyzed by comparison with the data in Materials Project Database (MPD) to examine the alloys which may occur phase separation or transition.",1702.02734v1 2017-10-24,Evaluation of microstructure and mechanical property variations in AlxCoCrFeNi high entropy alloys produced by a high-throughput laser deposition method,"Twenty-one distinct AlxCoCrFeNi alloys were rapidly prepared by laser alloying an equiatomic CoCrFeNi substrate with Al powder to create an alloy library ranging x=0.15-1.32. Variations in crystal structure, microstructure and mechanical properties were investigated using X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy and nanoindentation. With increasing Al content, the crystal structure transitioned from a disordered FCC to a mixture of disordered BCC and ordered B2 structures. While the onset of BCC/B2 formation was consistent with previously reported cast alloys, the FCC structure was observed at larger Al contents in the laser processed materials, resulting in a wider two phase regime. The FCC phase was primarily confined to the BCC/B2 grain boundaries at these high Al contents. The nanoindentation modulus and hardness of the FCC phase increased with Al content, while the properties of the BCC/B2 structure were insensitive to composition. The structure and mechanical properties of the laser-processed alloys were surprisingly consistent with reported results for cast alloys, demonstrating the feasibility of applying this high-throughput methodology to multicomponent alloy design.",1710.08855v1 2021-05-06,Anticorrosion and biocompatibility of a functionalized layer formed on ZK60 Mg alloy via hydroxyl ion implantation,"Magnesium and its alloys have aroused tremendous interests because of their promising mechanical properties and biocompatibility. However, their excessively fast corrosion rate hinders the development of Mg alloys in the biomedical fields. Inspired by conventional ion implantation, a less-toxic functional group (hydroxyl) is used as the ion source to bombard the ZK60 Mg alloy surface to form a functionalized oxide layer. This functionalized oxide layer significantly facilitates the corrosion resistance of the ZK60 Mg alloy substrate and the proliferation of MC3T3-E1 cells, which is confirmed by electrochemical, immersion, and in vitro cytocompatibility tests. In comparison with results of ZK60 alloy implanted with carboxyl ions in our previous work, it is concluded that hydroxyl-treated alloys exhibit slightly higher corrosion rate while better biocompatibility. In summary, less-toxic functional ion implantation can be an effective strategy for inhibiting corrosion of Mg alloy implants and promoting their biocompatibility.",2105.02558v1 2022-01-12,Hydrogen trapping and embrittlement in high-strength Al-alloys,"Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles. High-strength Al-alloys often used in aircrafts could help reduce the weight of automobiles, but are susceptible to environmental degradation. Hydrogen (H) ""embrittlement"" is often pointed as the main culprit, however, the mechanisms underpinning failure are elusive: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the materials' durability. Here we successfully performed near-atomic scale analysis of H trapped in second-phase particles and at grain boundaries in a high-strength 7xxx Al-alloy. We used these observations to guide atomistic ab-initio calculations which show that the co-segregation of alloying elements and H favours grain boundary decohesion, while the strong partitioning of H into the second-phases removes solute H from the matrix, hence preventing H-embrittlement. Our insights further advance the mechanistic understanding of H-assisted embrittlement in Al-alloys, emphasizing the role of H-traps in retarding cracking and guiding new alloy design.",2201.04490v1 2022-05-18,Atomistic Investigation of Elementary Dislocation Properties Influencing Mechanical Behaviour of $Cr_{15}Fe_{46}Mn_{17}Ni_{22}$ alloy and $Cr_{20}Fe_{70}Ni_{10}$ alloy,"In this work, molecular dynamics (MD) simulations were used to investigate elementary dislocation properties in a Co-free high entropy (HEA) model alloy ($Cr_{15}Fe_{46}Mn_{17}Ni_{22}$ at. %) in comparison with a model alloy representative of Austenitic Stainless Steel (ASS) ($Cr_{20}Fe_{70}Ni_{10}$ at. %). Recently developed embedded-atom method (EAM) potentials were used to describe the atomic interactions in the alloys. Molecular Statics (MS) calculations were used to study the dislocation properties in terms of local stacking fault energy (SFE), dissociation distance while MD was used to investigate the dissociation distance under applied shear stress as a function of temperature and strain rate. It was shown that higher critical stress is required to move dislocations in the HEA alloy compared with the ASS model alloy. The theoretical investigation of simulation results of the dislocation mobility shows that a simple constitutive mobility law allows to predict dislocation velocity in both alloys over three orders of magnitude, covering the phonon drag regime and the thermally activated regime induced by dislocation unpinning from local hard configurations.",2205.08798v1 2022-05-25,"Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys","We present a comprehensive first-principles investigation of optical, transport, and thermoelectric properties of pure and doped hexagonal Si$_x$Ge$_{1-x}$ alloys based on density-functional theory calculations, the Boltzmann transport equation, and the generalized quasi-chemical approximation to obtain alloy averages of electronic properties. At low temperature, phase decomposition into the hexagonal elementary crystals is thermodynamically favored, but around and above room temperature random alloys are predicted to be stable. While hexagonal Si has an indirect band gap, the gap of hexagonal Ge is direct with very weak optical transitions at the absorption edge. The alloy band gap remains direct for a Si content below 45\,\% and the oscillator strength of the lowest optical transitions is efficiently enhanced by alloying. The optical spectra show clear trends and both absorption edges and prominent peaks can be tuned with composition. The dependence of transport coefficients on carrier concentration and temperature is similar in cubic and hexagonal alloys. However, the latter display anisotropic response due to the reduced hexagonal symmetry. In particular, the transport mass exhibits a significant directional dependence. Seebeck coefficients and thermoelectric power factors of $n$-doped alloys show non-monotonous variations with the Si content independently of temperature.",2205.12612v1 2022-09-11,A map of single-phase high-entropy alloys,"High-entropy alloys have shown much interest and unusual materials properties. The stability of equimolar single-phase solid solution of five or more elements is likely to be rare and identifying the existence of such alloys has been very challenging because of the very large space of possible combinations. Herein, based on high-throughput density-functional theory calculations, we construct a chemical map of single-phase equimolar high entropy alloys by investigating over 650000 equimolar quinary alloys through a binary regular solid-solution model. We identify more than 30000 potential single-phase equimolar alloys (5% of the possible combinations) forming mainly in body-centered cubic structures. We unveil the chemistries that are likely to form high-entropy alloys, and identify the complex interplay among mixing enthalpy, intermetallics formation, and melting point that drives the formation of these solid solutions. We demonstrate the power of our method by predicting the existence of two new high entropy alloys, i.e. the body-centered cubic AlCoMnNiV and the face-centered cubic CoFeMnNiZn, which are successfully synthesized.",2209.04803v3 2022-10-17,A new alloy for Al-chalcogen system: AlSe surface alloy on Al (111),"Metal chalcogenide is a promising material for studying novel underlying physical phenomena and nanoelectronics applications. Here, we systematically investigate the crystal structure and electronic properties of the AlSe surface alloy on Al (111) using scanning tunneling microscopy, angle-resolved photoelectron spectrometer, and first-principle calculations. We reveal that the AlSe surface alloy possesses a hexagonal closed-packed structure. The AlSe surface alloy comprises two atomic sublayers (Se sublayer and Al sublayer) with 1.16 A along the z direction. The dispersion shows two hole-like bands for AlSe surface alloy located at about -2.2 eV, far below the Fermi level, which is sharply different from other metal chalcogenide and binary alloys. These two bands mainly derive from the in-plane orbital of AlSe (px and py). These results provide implications for related Al-chalcogen interface. Meanwhile, AlSe alloy have an advantage of large-scale atomic flatness and a wide band gap near the Fermi level in serving as an interface for two-dimensional materials.",2210.08739v1 2023-07-31,Structural and Magnetic Properties of V-Ti-Si Alloy Superconductors,"The structural and magnetic properties of the as-cast and annealed V$_{0.6-x}$Si$_x$Ti$_{0.4}$ ($x$ = 0, 0.05, 0.10, 0.15) alloy superconductors are reported here. It is found that addition of silicon to the V-Ti alloys results in eutectic precipitation of Ti$_{5}$Si$_3$-phase in the body centred cubic (bcc) $\beta$-V-Ti matrix. In the as-cast V$_{0.6-x}$Si$_x$Ti$_{0.4}$ alloys, the superconducting transition temperature (T$_{C}$) changes non-monotonically with increasing silicon content whereas after annealing, it is about 7.7 K for all the alloys. On the other hand, the upper critical field decreases and the coherence length increases after annealing in the x = 0.10 alloy. The variations in the superconducting properties in the alloys are related to the solubility of 6 at.% Si in the V$_{0.60}$Ti$_{0.40}$ alloy and the vanadium enrichment in the $\beta$ matrix due to the precipitation of Ti$_{5}$Si$_3$ phase.",2307.16623v2 2023-10-06,Multi-principal element alloy discovery using directed energy deposition and machine learning,"Multi-principal element alloys open large composition spaces for alloy development. The large compositional space necessitates rapid synthesis and characterization to identify promising materials, as well as predictive strategies for alloy design. Additive manufacturing via directed energy deposition is demonstrated as a high-throughput technique for synthesizing alloys in the Cr-Fe-Mn-Ni quaternary system. More than 100 compositions are synthesized in a week, exploring a broad range of compositional space. Uniform compositional control to within +/-5 at% is achievable. The rapid synthesis is combined with conjoint sample heat treatment (25 samples vs 1 sample), and automated characterization including X-ray diffraction, energy-dispersive X-ray spectroscopy, and nano-hardness measurements. The datasets of measured properties are then used for a predictive strengthening model using an active machine learning algorithm that balances exploitation and exploration. A learned parameter that represents lattice distortion is trained using the alloy compositions. This combination of rapid synthesis, characterization, and active learning model results in new alloys that are significantly stronger than previous investigated alloys.",2310.04021v1 1999-08-03,The Fermi surfaces of Metallic Alloys and the Oscillatory Magnetic Coupling between Magnetic Layers separated by such Alloy Spacers,"We review the theory of oscillatory magnetic coupling in Metallic Multilayers across alloy spacers. We illustrate the relationship between the frequencies of the oscillations and the extremal caliper vectors of the Fermi surface of the spacer by explicit calculations for Cu$_{(1-x)}$Ni$_x$, Cr$_{(1-x)}$V$_x$ and Cr$_{(1-x)}$Mo$_x$ alloys. We argue the measurement of the frequencies of such oscillations can be an extremely useful and cheap probe of the Fermi surface of random alloys.",9908035v1 2004-01-31,"Comparison among the local atomic order of amorphous TM-Ti alloys (TM=Co, Ni, Cu) produced by Mechanical Alloying studied by EXAFS","We have investigated the local atomic structure of amorphous TM-Ti alloys (TM = Co, Ni, Cu) produced by Mechanical Alloying by means of EXAFS analyses on TM and Ti K-edges. Coordination numbers and interatomic distances for the four alloys where found and compared. EXAFS results obtained indicated a shortening in the unlike pairs TM-Ti as the difference between $d$ electrons of TM and Ti atoms increases, suggesting an increase in the chemical short range order (CSRO) from TM = Co to Cu.",0402013v1 2006-12-13,Tuning alloy disorder in diluted magnetic semiconductors in high fields to 89 T,"Alloy disorder in II-VI diluted magnetic semiconductors (DMS) is typically reduced when the local magnetic spins align in an applied magnetic field. An important and untested expectation of current models of alloy disorder, however, is that alloy fluctuations in many DMS compounds should increase again in very large magnetic fields of order 100 tesla. Here we measure the disorder potential in a Zn$_{.70}$Cd$_{.22}$Mn$_{.08}$Se quantum well via the low temperature photoluminescence linewidth, using a new magnet system to 89 T. Above 70 T, the linewidth is observed to increase again, in accord with a simple model of alloy disorder.",0612332v1 2006-12-26,Compaction of bulk amorphous Fe40Ni40P14B6 alloys,"The consolidations of two bulk amorphous Fe40Ni40P14B6 alloy discs are performed via hot pressing for a short time in its supercooled liquid region under a pressure of ~1.2 GPa. When the consolidated temperature Ts is lower, the conjunction of two bulk amorphous Fe40Ni40P14B6 alloy discs cannot be achieved. Only when Ts get to the vicinity of 675 K, two amorphous Fe40Ni40P14B6 alloy discs have low viscosity enough to be fully fused together in a short time and the resulting compacts retain ~90% amorphous phase. To further improve the consolidated temperature Ts, a vast amount of crystallization will occur and result in the embrittlement of amorphous alloy.",0612628v2 2008-05-21,Model Checking Event-B by Encoding into Alloy,"As systems become ever more complex, verification becomes more main stream. Event-B and Alloy are two formal specification languages based on fairly different methodologies. While Event-B uses theorem provers to prove that invariants hold for a given specification, Alloy uses a SAT-based model finder. In some settings, Event-B invariants may not be proved automatically, and so the often difficult step of interactive proof is required. One solution for this problem is to validate invariants with model checking. This work studies the encoding of Event-B machines and contexts to Alloy in order to perform temporal model checking with Alloy's SAT-based engine.",0805.3256v2 2008-12-03,Relationship between the magnetic hyperfine field and the magnetic moment,"Based on experimental data it is shown, for some chosen alloys and compounds of iron, that there is no one unique relationship between the 57Fe-site magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead, the Bhf-m plot consists of several branches, each of them being characteristic of a given alloy or compound. Consequently, the effective proportionality constant (hyperfine coupling constant) depends on the alloy system or compound, and for a given alloy system or compound it depends on the composition or even on the lattice site. Consequently, the scaling of Bhf into the underlying m cannot be done a priopri.",0812.0671v1 2009-06-08,"Multicomponent multisublattice alloys, nonconfigurational entropy and other additions to the Alloy Theoretic Automated Toolkit","A number of new functionalities have been added to the Alloy Theoretic Automated Toolkit (ATAT) since it was last reviewed in this journal in 2002. ATAT can now handle multicomponent multisublattice alloy systems, nonconfigurational sources of entropy (e.g. vibrational and electronic entropy), Special Quasirandom Structures (SQS) generation, tensorial cluster expansion construction and includes interfaces for multiple atomistic or ab initio codes. This paper presents an overview of these features geared towards the practical use of the code. The extensions to the cluster expansion formalism needed to cover multicomponent multisublattice alloys are also formally demonstrated.",0906.1608v1 2010-02-26,"Investigation on Vibrational, Optical and Structural Properties of an Amorphous Se$_{0.80}$S$_{0.20}$ Alloy Produced by Mechanical Alloying","An amorphous Se$_{0.80}$S$_{0.20}$ alloy produced by Mechanical Alloying was studied by Raman spectroscopy, x-ray diffraction, extended x-ray absorption fine structure (EXAFS) and optical absorption spectroscopy, and also through reverse Monte Carlo simulations of its total structure factor and EXAFS data. Its vibrational modes, optical gap and structural properties as average interatomic distances and average coordination numbers were determined and compared to those found for an amorphous Se$_{0.90}$S$_{0.10}$ alloy. The results indicate that coordination numbers, interatomic distances and also the gap energy depend on the sulphur concentration.",1002.5006v1 2018-02-27,Fitting of the TB-SMA interatomic potentials for Pt/Cu(111) surface alloy,"In this paper we present new parameters of the TB-SMA interatomic potentials for the Pt/Cu(111) surface alloy. The parameters are fitted using both the experimental and {\it ab initio} data. The potentials reproduce not only the bulk properties of copper and platinum, but also the energy characteristics of the Pt/Cu(111) surface alloy. The potentials can be used for the simulations of the growth of the Pt/Cu(111) surface alloy on the atomic scale.",1802.09965v1 2020-04-27,Analytic binary alloy volume-concentration relations and the deviation from Zen`s law,"Alloys expand or contract as concentrations change, and the resulting relationship between atomic volume and alloy content is an important property of the solid. While a well-known approximation posits that the atomic volume varies linearly with concentration (Zen`s law), the actual variation is more complicated. Here we use an apparent size of the solute (solvent) atom and the elasticity to derive explicit analytical expressions for the atomic volume of binary solid alloys. Two approximations, continuum and terminal, are proposed. Deviations from Zen`s law are studied for 22 binary alloy systems.",2004.12966v1 2020-05-17,Band structures and direct-to-indirect bandgap transitions in BAlN and BGaN alloys: a first principle study,"In this work, the energy band structures of BGaN and BAlN alloys are systematically studied through first-principles calculation using HSE hybrid density functional theory by MedeA-VASP. Direct-indirect bandgap transition of BGaN alloys at B content around 44% and that of BAlN alloys at B content about 24% have been identified. The variation of electron and hole effective masses of both materials at different B compositions have also been demonstrated. A large change in hole effective masses of BGaN and BAlN alloys from B=0% to 25% has been observed. Finally, a picture of energy bandgap versus lattice constant of III-nitride family with boron is shown.",2005.08274v1 2020-03-09,Uncommon clustering in dilute Ti-Fe alloys,"We present the results of ab initio modeling of structure of dilute Ti-Fe, a typical representative of quenched Ti-based transition-metal alloys. We have demonstrated that beyond the solubility limit this alloy cannot be described in common terms of substitutional and interstitial alloys. Instead, very stable local clusters are formed in both low-temperature hcp and high-temperature bcc phases of alloys, with almost identical local structures. This gives an example of geometrically frustrated state and explains unusual concentration behavior of M\""ossbauer spectra discovered long ago for this system.",2003.03939v1 2020-09-24,Design using randomness: a new dimension for metallurgy,"High entropy alloys add a new dimension, atomic-scale randomness and the associated scale-dependent composition fluctuations, to the traditional metallurgical axes of time-temperature-composition-microstructure. Alloy performance is controlled by the energies and motion of defects (dislocations, grain boundaries, vacancies, cracks, ...). Randomness at the atomic scale can introduce new length and energy scales that can control defect behavior, and hence control alloy properties. The axis of atomic-scale randomness combined with the huge compositional space in multicomponent alloys thus enables, in tandem with still-valid traditional principles, a new broader alloy design strategy that may help achieve the multi-performance requirements of many engineering applications.",2009.11740v1 2024-02-19,High-entropy alloy TiV2ZrCrMnFeNi for hydrogen storage at room temperature with full reversibility and good activation,"The development of alloys that are hydrogenated and dehydrogenated quickly and actively at room temperature is a challenge for the safe and compact storage of hydrogen. In this study, a new high-entropy alloy (HEA) with AB-type configuration (A: hydride-forming elements, B: inert-to-hydrogen elements) was designed by considering valence electron concentration, electronegativity difference and atomic-size mismatch of elements. The alloy TiV2ZrCrMnFeNi had dual C14 Laves and BCC phases, in which C14 stored hydrogen and BCC/C14 interphase boundaries contributed to activation. The alloy absorbed 1.6 wt% of hydrogen at room temperature without any activation treatment and exhibited fast kinetics and full reversibility.",2402.11781v1 2017-11-17,First principles second harmonic generation of transition metal dichalcogenides and boron nitride alloys: from monolayers and nanotubes to Haeckelites and Schwarzites,"In order to shed light on the second harmonic generation (SHG) of new 2-D systems, first principles methods are used to calculate the second order susceptibility \chi(2) for different types of layered alloys such as monolayers of transition metal dichalcogenide (TMD) alloys, TMD Haeckelite alloys, nanotubes of TMD alloys, hexagonal boron nitride (h-BN) systems which include BxNyCz alloys, BN and BNC2 nanotubes, BxNxCy Haeckelites and BN Schwarzites (porous BN). It is found that the tungsten based alloys possess higher \chi(2) than Mo based at high photon energies, but at low energies, one type of MoSSe dominates. The hypothetical TMD Haeckelites NbSSe and Nb0.5Ta0.5S2 reveal the highest \chi(2) of all the calculated structures. Zigzag TMD alloy nanotubes show higher \chi(2) as the diameter is reduced and approximate to the monolayer for big diameters. BNC alloys exhibit a higher \chi(2) than the h-BN monolayer and are comparable to TMD alloys, except for one case which doubles its intensity. The BN tubes show an increase of \chi(2) as the diameter decreases, similarly to the TMD nanotubes. BxNxCy Haeckelites possess a very high \chi(2) and may shed light on the role of extended defects in nonlinear optical properties. One of the BN Schwarzites exhibits a higher \chi(2) than already known 3-D materials.",1711.06751v1 2019-01-07,Mechanistic origin of high retained strength in refractory BCC high entropy alloys up to 1900K,"The body centered cubic (BCC) high entropy alloys MoNbTaW and MoNbTaVW show exceptional strength retention up to 1900K. The mechanistic origin of the retained strength is unknown yet is crucial for finding the best alloys across the immense space of BCC HEA compositions. Experiments on Nb-Mo, Fe-Si and Ti-Zr-Nb alloys report decreased mobility of edge dislocations, motivating a theory of strengthening of edge dislocations in BCC alloys. Unlike pure BCC metals and dilute alloys that are controlled by screw dislocation motion at low temperatures, the strength of BCC HEAs can be controlled by edge dislocations, and especially at high temperatures, due to the barriers created for edge glide through the random field of solutes. A parameter-free theory for edge motion in BCC alloys qualitatively and quantitatively captures the strength versus temperature for the MoNbTaW and MoNbTaVW alloys. A reduced analytic version of the theory then enables screening over >600,000 compositions in the Mo-Nb-Ta-V-W family, identifying promising new compositions with high retained strength and/or reduced mass density. Overall, the theory reveals an unexpected mechanism responsible for high temperature strength in BCC alloys and paves the way for theory-guided design of stronger high entropy alloys.",1901.02100v3 2020-05-23,Mixed ground state in Fe-Ni Invar alloys,"We investigate the ground state properties of Invar alloys via detailed study of the electronic structure of Fe$_{1-x}$Ni$_x$ alloys ($x$ = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9) employing $x$-ray photoelectron spectroscopy (XPS). While all the alloys exhibit soft ferromagnetic behavior with Curie temperature much higher than the room temperature, the results for invar alloy, Fe$_{0.6}$Ni$_{0.4}$ exhibit anomalous behavior. Moreover, the magneto-resistance of the Invar alloy becomes highly negative while the end members possess positive magneto-resistance. The core level spectra of the Invar alloy exhibit emergence of a distinct new feature below 20~K while all other Fe-Ni alloys exhibit no temperature dependence down to 10~K. Interestingly, the shallow core level spectra (3$s$, 3$p$) of Fe and Ni of the Invar alloy reveal stronger deviation at low temperatures compared to the deep core levels (2$s$, 2$p$) indicating crystal field effect. It appears that there is a large precipitation of antiferromagnetic $\gamma^\prime$ phase below 20 K possessing low magnetic moment (0.5$\mu_B$) on Fe within the $\alpha$ phase. The discovery of negative magneto-resistance, anomalous magnetization at low temperature and the emergence of unusual new features in the core levels at low temperature provide an evidence of mixed phase in the ground state of Invar alloys.",2005.11493v1 2020-08-24,Bond Synergy Model for Bond Energies in Alloy Oxides,"In this work we introduce a metal-oxide bond-energy model for alloy oxides based on pure-phase bond energies and bond synergy factors that describe the effect of alloying on the bond energy between cations and oxygen, an important quantity to understand formation and stability of passive films. This model is parameterized for binary cation-alloy oxides using density-functional theory energies and is shown to be directly transferable to multi-component alloy oxides. We parameterized the model for alloy oxide energies with metal cations that form the basis of corrosion resistant alloys, including Fe, Ni, Cr, Mo, Mn, W, Co, and Ru. We find that isoelectronic solutes allow quantification of pure-phase bond energies in oxides and that the calculated bond energy values give sensible results compared to common experience, including the role of Cr as the passive-layer former in Fe-Ni-Cr alloys for corrosion applications. Additionally, the bond synergy factors give insights into the mutual strengthening and weakening effects of alloying on cation-oxygen bonds and can be related to enthalpy of mixing and charge neutrality constraints. We demonstrate how charge neutrality can be identified and achieved by the oxidation states that the different cations assume depending on alloy composition and the presence of defects.",2008.10172v1 2021-11-23,Atomic and mesoscopic structure of Dy-based surface alloys on noble metals,"Surface alloys are a highly tunable class of low dimensional materials with the opportunity to tune and control the spin and charge carrier functionalities on the nanoscale. Here, we focus on the atomic and mesoscopic structural details of three distinctive binary rare-earth-noble metals (RE/NM) surface alloys by employing scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Using Dysprosium as the guest element on fcc(111) noble metal substrates, we identify the formation of non-commensurate surface alloy superstructures which exhibit homogeneous moir\'e patterns for DyCu2/Cu (111) and DyAu2/Au(111), while an inhomogeneous one is found for DyAg2/Ag(111). The variations in the local structure are analyzed for all three surface alloys and the observed differences are discussed in the light of the lattice mismatches of the alloy layer with respect to the underlying substrate. For the particularly intriguing case of a Dy-Ag surface alloy, the surface alloy layer does not show a uniform long-range periodic structure, but consists of local hexagonal tiles separated by extended domain walls. These domain walls exist to relief the in-plane strain within the DyAg2 surface alloy layer. Our findings clearly demonstrate that surface alloying is an intriguing tool to tailor both the local atomic, but also the mesoscopic moir\'e structures of metallic heterostructures.",2111.11877v2 2023-04-09,High-throughput Alloy and Process Design for Metal Additive Manufacturing,"Designing alloys for additive manufacturing (AM) presents significant opportunities. Still, the chemical composition and processing conditions required for printability (ie., their suitability for fabrication via AM) are challenging to explore using solely experimental means. In this work, we develop a high-throughput (HTP) computational framework to guide the search for highly printable alloys and appropriate processing parameters. The framework uses material properties from state-of-the-art databases, processing parameters, and simulated melt pool profiles to predict process-induced defects, such as lack-of-fusion, keyholing, and balling. We accelerate the printability assessment using a deep learning surrogate for a thermal model, enabling a 1,000-fold acceleration in assessing the printability of a given alloy at no loss in accuracy when compared with conventional physics-based thermal models. We verify and validate the framework by constructing printability maps for the CoCrFeMnNi Cantor alloy system and comparing our predictions to an exhaustive 'in-house' database. The framework enables the systematic investigation of the printability of a wide range of alloys in the broader Co-Cr-Fe-Mn-Ni HEA system. We identified the most promising alloys that were suitable for high-temperature applications and had the narrowest solidification ranges, and that was the least susceptible to balling, hot-cracking, and the formation of macroscopic printing defects. A new metric for the global printability of an alloy is constructed and is further used for the ranking of candidate alloys. The proposed framework is expected to be integrated into ICME approaches to accelerate the discovery and optimization of novel high-performance, printable alloys.",2304.04149v1 2016-10-07,Computational Investigation of Half-Heusler Compounds for Spintronics Applications,"We present first-principles density functional calculations of the electronic structure, magnetism, and structural stability of 378 $\textit{XYZ}$ half-Heusler compounds (with $X=$ Cr, Mn, Fe, Co, Ni, Ru, Rh, $Y=$ Ti, V, Cr, Mn, Fe, Ni, $Z=$ Al, Ga, In, Si, Ge, Sn, P, As, Sb). We find that a ""Slater-Pauling density of states"" with a gap or pseudogap at three states per atom below the gap in at least one spin channel is a common feature in half-Heusler compounds. We find that the presence of such a gap at the Fermi energy in one or both spin channels contributes greatly to the stability of a half-Heusler compound. We calculate the formation energy of each compound and systematically investigate its stability against all other phases in the Open Quantum Materials Database (OQMD). We represent the thermodynamic phase stability of each compound as its distance from the convex hull of stable phases in the respective chemical space and show that the hull distance of a compound is a good measure of the likelihood of its experimental synthesis. We identify 26 18-electron semiconductors, 45 half-metals, and 34 near half-metals with negative formation energy, that follow the Slater-Pauling rule of three electrons per atom. Our calculations predict new thermodynamically stable semiconducting phases NiScAs, RhTiP, and RuVAs, which merit further experimental exploration. Further, two interesting zero-moment half-metals, CrMnAs and MnCrAs, are calculated to have negative formation energy. In addition, our calculations predict a number of new, hitherto unreported, semiconducting (e.g., CoVGe, FeVAs), half-metallic (e.g., RhVSb), near half-metallic (e.g., CoFeSb, CoVP) half-Heusler compounds to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for various spintronics applications.",1610.02444v2 2017-12-06,Computational Investigation of Inverse-Heusler compounds for Spintronics Applications,"First-principles calculations of the electronic structure, magnetism and structural stability of inverse-Heusler compounds with the chemical formula \textit{X$_2$YZ} are presented and discussed with a goal of identifying compounds of interest for spintronics. Compounds for which the number of electrons per atom for \textit{Y} exceed that for \textit{X} and for which \textit{X} is one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu; \textit{Y} is one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn; and \textit{Z} is one of Al, Ga, In, Si, Ge, Sn, P, As or Sb were considered. The formation energy per atom of each compound was calculated. By comparing our calculated formation energies to those calculated for phases in the Inorganic Crystal Structure Database (ICSD) of observed phases, we estimate that inverse-Heuslers with formation energies within 0.052 eV/atom of the calculated convex hull are reasonably likely to be synthesizable in equilibrium. The observed trends in the formation energy and relative structural stability as the \textit{X}, \textit{Y} and \textit{Z} elements vary are described. In addition to the Slater-Pauling gap after 12 states per formula unit in one of the spin channels, inverse-Heusler phases often have gaps after 9 states or 14 states. We describe the origin and occurrence of these gaps. We identify 14 inverse-Heusler semiconductors, 51 half-metals and 50 near half-metals with negative formation energy. In addition, our calculations predict 4 half-metals and 6 near half-metals to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for future spintronics applications.",1712.02278v1 2017-04-06,A critical study of the elastic properties and stability of Heusler compounds: Cubic Co$_{2}YZ$ compounds with $L2_{1}$ structure,"Elastic constants and their derived properties of various cubic Heusler compounds were calculated using first-principles density functional theory. To begin with, Cu$_2$MnAl is used as a case study to explain the interpretation of the basic quantities and compare them with experiments. The main part of the work focuses on Co$_2$-based compounds that are Co$_2$Mn$M$ with the main group elements $M=$~Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, and Co$_2TM$ with the main group elements Si or Ge, and the $3d$ transition metals $T=$~Sc, Ti, V, Cr, Mn, and Fe. It is found that many properties of Heusler compounds correlate to the mass or nuclear charge $Z$ of the main group element. Blackman's and Every's diagrams are used to compare the elastic properties of the materials, whereas Pugh's and Poisson's ratios are used to analyze the relationship between interatomic bonding and physical properties. It is found that the {\it Pugh's criterion} on brittleness needs to be revised whereas {\it Christensen's criterion} describes the ductile--brittle transition of Heusler compounds very well. The calculated elastic properties give hint on a metallic bonding with an intermediate brittleness for the studied Heusler compounds. The universal anisotropy of the stable compounds has values in the range of $0.57 0.005), an enhancement of the diffusion rates of all substitutional elements is seen. A model is suggested that relates the self-diffusivities in the CoCrFeMnNi-C alloys with the lattice distortion imposed by interstitially dissolved carbon. The experimental results are interpreted in terms of a decrease of the migration barriers for vacancy-mediated diffusion due to the presence of interstitial C atoms.",2112.10507v1 2022-04-24,High-throughput characterization of transition metal dichalcogenide alloys: Thermodynamic stability and electronic band alignment,"Alloying offers a way to tune many of the properties of the transition metal dichalcogenide (TMD) monolayers. While these systems in many cases have been thoroughly investigated previously, the fundamental understanding of critical temperatures, phase diagrams and band edge alignment is still incomplete. Based on first principles calculations and alloy cluster expansions we compute the phase diagrams 72 TMD monolayer alloys and classify the mixing behavior. We show that ordered phases in general are absent at room temperature but that there exists some alloys, which have a stable Janus phase at room temperature. Furthermore, for a subset of these alloys, we quantify the band edge bowing and show that the band edge positions for the mixing alloys can be continuously tuned in the range set by the boundary phases.",2204.11223v1 2022-05-06,Band lineup at hexagonal Si$_x$Ge$_{1-x}$/Si$_y$Ge$_{1-y}$ alloy interfaces,"The natural and true band profiles at heterojunctions formed by hexagonal Si$_x$Ge$_{1-x}$ alloys are investigated by a variety of methods: density functional theory for atomic geometries, approximate quasiparticle treatments for electronic structures, different band edge alignment procedures, and construction of various hexagonal unit cells to model alloys and heterojunctions. We demonstrate that the natural band offsets are rather unaffected by the choice to align the vacuum level or the branch point energy, as well as by the use of a hybrid or the Tran-Blaha functional. At interfaces between Ge-rich alloys we observe a type-I heterocharacter with direct band gaps, while Si-rich junctions are type-I but with an indirect band gap. The true band lineups at pseudomorphically grown heterostructures are strongly influenced by the generated biaxial strain of opposite sign in the two adjacent alloys. Our calculations show that the type-I character of the interface is reduced by strain. To prepare alloy heterojunctions suitable for active optoelectronic applications, we discuss how to decrease the compressive biaxial strain at Ge-rich alloys.",2205.03287v1 2022-07-24,MD simulations and experiments of plasma proteins adsorption to the biodegradable magnesium alloys to facilitate cell response,"Once the magnesium alloy was implanted in the body, it was immediately covered with plasma proteins. The coated alloy surface promoted the adsorption and growth of osteoblasts. Herein, in vitro biological reactions of the ZK60 and AZ31 magnesium alloys were analyzed with and without plasma proteins incubation. The plasma proteins adsorbed on the magnesium alloy were characterized using mass spectrometry (MS). The MS results show that proteins related to bone cells such as fibrinogen, vitronectin, fibronectin, and prothrombin are prone to adsorbed on the surface of the alloys than other proteins. These proteins restrain the degradation of Mg alloys and promote the adsorption and growth of bone cells, which demonstrated by the immersion tests and biocompatibility assays. Furthermore, molecular dynamics simulations were used to analyze the details of the adsorptions of fibrinogen, fibronectin, and prothrombin on ZK60 and AZ31at atomic level. It is revealed that the type of residues adsorbed on the surface of the material has an important effect on protein adsorption.",2207.11639v1 2022-09-06,Magnetization controlled by crystallization in soft magnetic Fe-Si-B-P-Cu alloys,"Soft magnetic materials have low coercive fields and high permeability. Recently, nanocrystalline alloys obtained using annealing amorphous alloys have attracted much interest since nanocrystalline alloys with small grain sizes of tens of nanometers exhibit low coercive fields comparable to that of amorphous alloys. Since nanocrystalline soft magnetic materials attain remarkable soft magnetic properties by controlling the grain size, the crystal grains' microstructure has a substantial influence on the soft magnetic properties. In this research, we examined the magnetic properties of Fe-Si-B-P-Cu nanocrystalline soft magnetic alloys obtained by annealing amorphous alloys. During crystallization, the observation findings reveal the correlation between the generated microstructures and soft magnetic properties.",2209.02225v1 2022-09-22,Computational Design of Corrosion-resistant and Wear-resistant Titanium Alloys for Orthopedic Implants,"Titanium alloys are promising candidates for orthopedic implants due to their mechanical resilience and biocompatibility. Current titanium alloys in orthopedic implants still suffer from low wear and corrosion resistance. Here, we present a computational method for optimizing the composition of titanium alloys for enhanced corrosion and wear resistance without compromising on other aspects such as phase stability, biocompatibility, and strength. We use the cohesive energy, oxide formation energy, surface work function, and the elastic shear modulus of pure elements as proxy descriptors to guide us towards alloys with enhanced wear and corrosion resistance. For the best-selected candidates, we then use the CALPHAD approach, as implemented in the Thermo-Calc software, to calculate the phase diagram, yield strength, hardness, Pourbaix diagram, and the Pilling-Bedworth (PB) ratio. These calculations are used to assess the thermodynamic stability, biocompatibility, corrosion resistance, and wear resistance of the selected alloys. Additionally, we provide insights about the role of silicon on improving the corrosion and wear resistance of alloys.",2210.00845v1 2022-11-23,The Mixing Thermodynamics and Local Structure of High-entropy Alloys from Randomly Sampled Ordered Configurations,"A general method is presented for modeling high entropy alloys as ensembles of randomly sampled, ordered configurations on a given lattice. Statistical mechanics is applied post hoc to derive the ensemble properties as a function of composition and temperature, including the free energy of mixing and local structure. Random sampling is employed to address the high computational costs needed to model alloys with a large number of components. Doing so also provides rigorous convergence criteria, including the quantification of noise due to random sampling, and an estimation of the number of additional samples required to lower this noise to the needed/desired levels. This method is well-suited for a variety of cases: i) high entropy alloys, where standard lattice models are costly; ii) ""medium"" entropy alloys, where both the entropy and enthalpy play significant roles; and iii) alloys with residual short-range order. Binary to 5-component alloys of the group-IV chalcogenides are used as case examples, for which the predicted miscibility shows excellent agreement with experiment.",2211.13066v1 2024-01-31,Spark Plasma Sintering for high-speed diffusion welding of the ultrafine grained near-a Ti-5Al-2V alloy with high strength and corrosion resistance for nuclear engineering,"The paper demonstrates the prospects of Spark Plasma Sintering (SPS) for the high-speed diffusion welding of the high-strength ultrafine-grained (UFG) near-a Ti-5Al-2V alloy. The effect of increased diffusion welding intensity in the UFG Ti alloys is discussed also. The welds of the UFG near-a-Ti-5Al-2V alloy obtained by SPS are featured by high density, strength, and corrosion resistance. The rate of weld sealing in the UFG alloys has been shown to depend on the heating rate non-monotonously (with a pronounced maximum). At the stage of continuous heating and isothermic holding, the kinetics of the weld sealing was found to be determined by the exponential creep rate, the intensity of which in the coarse-grained (CG) alloys is limited by the diffusion rate in the crystal lattice whereas in the UFG alloys it is limited by the grain boundary diffusion rate.",2401.17718v1 2024-02-27,A survey of energies from pure metals to multi-principal element alloys,"In materials science, a wide range of properties of materials are governed by various types of energies, including thermal, physicochemical, structural, and mechanical energies. In 2005, Dr. Frans Spaepen used crystalline face-centered-cubic (fcc) copper as an example to discuss a variety of phenomena that are associated with energies. Inspired by his pioneering work, we broaden our analysis to include a selection of representative pure metals with fcc, hexagonal close-packed (hcp), and body-centered cubic (bcc) structures. Additionally, we extend our comparison to energies between pure metals and equiatomic binary, ternary, and multi-principal element alloys (sometimes also known as high-entropy alloys). Through an extensive collection of data and calculations, we compile energy tables that provide a comprehensive view of how structure and alloying influence the energy profiles of these metals and alloys. We highlight the significant impact of constituent elements on the energies of alloys compared to pure metals and reveal a notable disparity in mechanical energies among materials in fcc-, hcp- and bcc-structured metals and alloys. Furthermore, we discuss the underlying mechanisms behind these patterns and discuss the implications for structural transformations, providing insights into the broader context of these energy variations.",2402.17121v1 2015-05-16,Substrate-free layer-number identification of two-dimensional materials: A case of Mo$_{0.5}$W$_{0.5}$S$_2$ alloy,"Any of two or more two-dimensional (2D) materials with similar properties can be alloyed into a new layered material, namely, 2D alloy. Individual monolayer in 2D alloys are kept together by Van der Waals interactions. The property of multilayer alloys is a function of their layer number. Here, we studied the shear (C) and layer-breathing (LB) modes of Mo$_{0.5}$W$_{0.5}$S$_2$ alloy flakes and their link to the layer number of alloy flakes. The study reveals that the disorder effect is absent in the C and LB modes of 2D alloys, and the monatomic chain model can be used to estimate the frequencies of the C and LB modes. We demonstrated how to use the C and LB mode frequency to identify the layer number of alloy flakes deposited on different substrates. This technique is independent of the substrate, stoichiometry, monolayer thickness and complex refractive index of 2D materials, offering a robust and substrate-free approach for layer-number identification of 2D materials.",1505.04236v1 2017-12-20,Impact of disorder on the optoelectronic properties of GaN$_y$As$_{1-x-y}$Bi$_x$ alloys and heterostructures,"We perform a systematic theoretical analysis of the nature and importance of alloy disorder effects on the electronic and optical properties of GaN$_{y}$As$_{1-x-y}$Bi$_{x}$ alloys and quantum wells (QWs), using large-scale atomistic supercell electronic structure calculations based on the tight-binding method. Using ordered alloy supercell calculations we also derive and parametrise an extended basis 14-band \textbf{k}$\cdot$\textbf{p} Hamiltonian for GaN$_{y}$As$_{1-x-y}$Bi$_{x}$. Comparison of the results of these models highlights the role played by short-range alloy disorder -- associated with substitutional nitrogen (N) and bismuth (Bi) incorporation -- in determining the details of the electronic and optical properties. Systematic analysis of large alloy supercells reveals that the respective impact of N and Bi on the band structure remain largely independent, a robust conclusion we find to be valid even in the presence of significant alloy disorder where N and Bi atoms share common Ga nearest neighbours. Our calculations reveal that N- (Bi-) related alloy disorder strongly influences the conduction (valence) band edge states, leading in QWs to strong carrier localisation, as well as inhomogeneous broadening and modification of the conventional selection rules for optical transitions. Our analysis provides detailed insight into key properties and trends in this unusual material system, and enables quantitative evaluation of the potential of GaN$_{y}$As$_{1-x-y}$Bi$_{x}$ alloys for applications in photonic and photovoltaic devices.",1712.07693v2 2020-08-08,"Screening of generalized stacking fault energies, surface energies and intrinsic ductile potency of refractory multicomponent alloys","Body-centered cubic (bcc) refractory multicomponent alloys are of great interest due to their remarkable strength at high temperatures. Meanwhile, further optimizing the chemical compositions of these alloys to achieve a combination of high strength and room-temperature ductility remains challenging, which would require systematic predictions of the correlated alloy properties across a vast compositional space. In the present work, we performed first-principles calculations with the special quasi-random structure (SQS) method to predict the unstable stacking fault energy ($\gamma_{usf}$) of the $(1\bar10)[111]$ slip system and the $(1\bar10)$-plane surface energy ($\gamma_{surf}$) for 106 individual binary, ternary and quaternary bcc solid-solution alloys with constituent elements among Ti, Zr, Hf, V, Nb, Ta, Mo, W, Re and Ru. Moreover, with the first-principles data and a set of physics-informed descriptors, we developed surrogate models based on statistical regression to accurately and efficiently predict $\gamma_{usf}$ and $\gamma_{surf}$ for refractory multicomponent alloys in the 10-element compositional space. Building upon binary and ternary data, the surrogate models show outstanding predictive ability in the high-order multicomponent systems. The ratio between $\gamma_{surf}$ and $\gamma_{usf}$ is a parameter to reflect the potency of intrinsic ductility of an alloy based on the Rice model of crack-tip deformation. Therefore, using the surrogate models, we performed a systematic screening of $\gamma_{usf}$, $\gamma_{surf}$ and their ratio over 112,378 alloy compositions to search for alloy candidates that may have enhanced strength-ductile synergies. Search results were also confirmed by additional first-principles calculations.",2008.03591v1 2022-03-24,Mode- and Space- Resolved Thermal Transport of Alloy Nanostructures,"Nanostructured semiconducting alloys obtain ultra-low thermal conductivity as a result of the scattering of phonons with a wide range of mean-free-paths (MFPs). In these materials, long-MFP phonons are scattered at the nanoscale boundaries whereas short-MFP high-frequency phonons are impeded by disordered point defects introduced by alloying. While this trend has been validated by simplified analytical and numerical methods, an ab-initio space-resolved approach remains elusive. To fill this gap, we calculate the thermal conductivity reduction in porous alloys by solving the mode-resolved Boltzmann transport equation for phonons using the finite-volume approach. We analyze different alloys, length-scales, concentrations, and temperatures, obtaining a very large reduction in the thermal conductivity over the entire configuration space. For example, a ~97% reduction is found for Al$_{0.8}$In$_{0.2}$As with 25% porosity. Furthermore, we employ these simulations to validate our recently introduced ""Ballistic Correction Model"" (BCM), an approach that estimates the effective thermal conductivity using the characteristic MFP of the bulk alloy and the length-scale of the material. The BCM is then used to provide guiding principles in designing alloy-based nanostructures. Notably, it elucidates how porous alloys such as Si$_{x}$Ge$_{1-x}$ obtain larger thermal conductivity reduction compared to porous Si or Ge, while also explaining why we should not expect similar behavior in alloys such as Al$_{x}$In$_{1-x}$As. By taking into account the synergy from scattering at different scales, we provide a route for the design of materials with ultra-low thermal conductivity.",2203.13279v1 2019-05-14,Discovery of $ω$-free high-temperature Ti-Ta-X shape memory alloys from first principles calculations,"The rapid degradation of the functional properties of many Ti-based alloys is due to the precipitation of the $\omega$ phase. In the conventional high-temperature shape memory alloy Ti-Ta the formation of this phase compromises completely the shape memory effect and high (>100{\deg}C) transformation temperatures cannot be mantained during cycling. A solution to this problem is the addition of other elements to form Ti-Ta-X alloys, which often modifies the transformation temperatures; due to the largely unexplored space of possible compositions, very few elements are known to stabilize the shape memory effect without decreasing the transformation temperatures below 100{\deg}C. In this study we use transparent descriptors derived from first principles calculations to search for new ternary Ti-Ta-X alloys that combine stability and high temperatures. We suggest four new alloys with these properties, namely Ti-Ta-Sb, Ti-Ta-Bi, Ti-Ta-In, and Ti-Ta-Sc. Our predictions for the most promising of these alloys, Ti-Ta-Sc, are subsequently fully validated by experimental investigations, the new alloy Ti-Ta-Sc showing no traces of $\omega$ phase after cycling. Our computational strategy is immediately transferable to other materials and may contribute to suppress $\omega$ phase formation in a large class of alloys.",1905.05680v3 2019-09-17,Sparking mashups to form multifunctional alloy nanoparticles,"Synthesizing unconventional alloys remains challenging owing to seamless interactions between kinetics and thermodynamics. High entropy alloys (HEAs), for example, draw a fundamentally new concept to enable exploring unknown regions in phase diagrams. The exploration, however, is hindered by traditional metallurgies based on liquid-solid transformation. Vapor-solid transformation that is permissible on pressure-temperature phase diagrams, offers the most kinetically efficient pathway to form any desired alloy (e.g., HEA). Here, we report that a technique called ""sparking mashups"", which involves a rapidly quenched vapor source and induces unrestricted mixing for alloying 55 distinct types of ultrasmall nanoparticles (NPs) with controllable compositions. Unlike the precursor feed in wet chemistry, a microseconds-long oscillatory spark controls the vapour composition, which is eventually retained in the alloy NPs. The resulting NPs range from binary to HEAs with marked thermal stability at room temperature. We show that a nanosize-effect ensures such thermal stability and mimics the role of mixing entropy in HEAs. This discovery contradicts the traditional ""smaller is less stable"" view while enabling the elemental combinations that have never been alloyed to date. We even break the miscibility limits by mixing bulk-immiscible systems in alloy NPs. As powerful examples, we demonstrate the alloy NPs as both high-performance fuel-cell catalysts and building blocks for three-dimensional (3D) nanoprinting to construct HEA nanostructure arrays of various architectures and compositions. Our results form the basis of new rules for guiding HEA-NP synthesis and advancing catalysis and 3D printing to new frontiers.",1909.08147v2 2024-01-30,Effect of the Sc/Zr ratio on the corrosion resistance of Al-Mg cast alloys,"The results of investigations of the corrosion resistance of Al-Mg-Sc-Zr alloys with varying Mg content and different Sc/Zr ratios are presented. The objects of investigations were the Al-Mg-Sc-Zr alloys with total Sc + Zr content of 0.32 wt%. The concentration of Sc and Zr in the alloys varied with the increments of 0.02 wt%. The alloys were produced by induction casting. The effect of annealing temperature on the microhardness and electrical resistivity of the Al-Mg-Sc-Zr alloys was investigated. Corrosion tests were carried out in a medium simulating intergranular corrosion in aluminum alloys. Electrochemical studies and mass loss tests were performed. An increase in the Sc concentration and a decrease in the Zr one were shown to result in an increase in the corrosion rate. The primary Al3(ScxZr1-x) particles were found to have the main effect on the corrosion resistance of Al-Mg-Sc-Zr alloys. The dependence of the corrosion current on the annealing temperature of the Al-Mg-Sc-Zr alloy was found to have a non-monotonous character (with a maximum).",2401.17429v1 2024-02-19,Hot carrier distribution engineering by alloying: picking elements for the desired purposes,"Metal alloys hold the promise of providing hot carrier generation distributions superior to pure metals in applications such as sensing, catalysis and solar energy harvesting. Guidelines for finding the optimal alloy configuration for a target application require understanding the connection between alloy composition and hot carrier distribution. Here we present a DFT-based computational approach to investigate the photo-generated hot carrier distribution of metal alloys based on the joint density of states and the electronic structure. We classified the metals by their electronic structure into closed d-shell, open d-shell, p-block and s-block elements. It is shown that combining closed d-shell elements enables modulating the distribution of highly energetic holes typical of pure metals but also leads to hot carrier production by IR light excitation and the appearance of highly energetic electrons due to band folding and splitting. This feature arises as an emergent property of alloying and is only unveiled when the hot carrier distribution computation takes momentum conservation into account. The combination of closed d-shell with open d-shell elements allows an abundant production of hot carriers in a broad energy range, while alloying a closed d-shell elements with an s-block element opens the door to hot electron distribution skewed toward high energy electrons. The combination of d-shell with p-block elements results in moderate hot carrier distribution whose asymmetry can be tuned by composition. Overall, the obtained insights that connect alloy composition, band structure and resulting carrier distribution provide a toolkit to match elements in an alloy for the deliberate engineering of hot carrier distribution.",2402.12337v1 2004-04-29,Aging-induced complex transformation behavior of martensite in Ni57.5Mn17.5Ga25 shape memory alloy,"Ni57.5Mn17.5Ga25 shape memory alloy exhibits a complex transformation behavior, appearing after aging. Aging in the austenitic state resulted in an ordinary decrease of the martensitic transformation temperature. Contrary to this, aging in the martensitic state brought about unusual features of the martensitic transformation observed so far only in Ni-Ti alloys.",0404698v1 2009-08-25,Augmented space recursion code and application in simple binary metallic alloy,"We present here an optimized and parallelized version of the {\sl augmented space recursion code} for the calculation of the electronic and magnetic properties of bulk disordered alloys, surfaces and interfaces, either flat, corrugated or rough, and random networks. Applications have been made to bulk disordered alloys to benchmark our code.",0908.3532v1 2013-01-22,"First principles study of helium, carbon and nitrogen in austenite, dilute austenitic iron alloys and nickel","An extensive set of first-principles density functional theory calculations have been performed to study the behaviour of He, C and N solutes in austenite, dilute Fe-Cr-Ni austenitic alloys and Ni in order to investigate their influence on the microstructural evolution of austenitic steel alloys under irradiation.",1301.5317v1 2018-01-10,Microstructure and mechanical properties of Al-Cu alloy with 0.6%Fe produced with ultrasonic vibration and applied pressure,"The combined effect of ultrasonic vibration (UT) and applied pressure (P) on microstructure and mechanical properties of Al-5.0Cu-0.6Mn-0.6Fe alloy were investigated. The best tensile properties produced by P+UT processing are UTS: 268MPa, YS: 192MPa, E.L.: 17.1%, respectively, which increasing by 64%, 59% and 307%, respectively, compare to the Non-treated alloy.",1801.03246v1 2021-07-03,Thin film of Al-Ga-Pd-Mn quasicrystalline alloy,"Thin film quasicrystal coatings have unique properties such as very high electrical and thermal resistivity and very low surface energy. A nano quasicrystalline thin film of icosahedral Al-Ga-Pd-Mn alloy, has produced by flash evaporation followed by annealing. Attempts will be made to discuss the micromechanisms for the formation of quasicrystalline thin film in Al-Ga-Pd-Mn alloys",2107.01478v1 2018-12-26,Formation and composition-dependent properties of alloys of cubic halide perovskites,"Distinct shortcomings of individual halide perovskites for solar applications, such as restricted range of band gaps, propensity of ABX3 to decompose into AX+BX2, or oxidation of 2ABX3 into A2BX6 have led to the need to consider alloys of individual perovskites. This creates a non-trivial material-selection problem, spanning a continuum of three sets of compositions (one for each sub lattice), and requiring control of phase-separation or ordering in each alloyed subfield. Not surprisingly, material and structure choices were made thus far mostly via trial-and-error explorations. We use ideas from solid state theory of semiconductor alloys to analyze the behaviors of the (FA,Cs)(Pb,Sn)I3 alloys system. Density functional calculations utilizing specially constructed supercells (SQS) are used to calculate the composition dependence of band gaps, energy of decomposition and alloy mixing enthalpies. A number of trends are observed for A-site as well as for B-site alloys. To understand the physical reasons that control these trends we decompose the alloy properties into distinct physical terms: (i) the energies associated with removing the octahedral deformations (tilting, rotations, B site displacements), (ii) the energies of compressing the larger component and expanding the smaller one to the alloy volume, (iii) the charge transfer energies associated with placing the alloyed units onto a common lattice, and finally, (iv) structural relaxation of all bonds within the cells., This analysis clarifies the origin of the observed trends in bang gaps, decomposition energies and mixing enthalpies. Unlike a number of previous calculations we find that the a proper description of alloy physics requires that even the pure, non-alloyed end-point compounds be allowed to develop local environment dependent octahedral deformation that lowers significantly the total energy and raises their band gaps.",1812.10536v1 1999-02-22,"La substitution induced linear temperature dependence of electrical resistivity and Kondo behavior in the alloys, Ce_{2-x}La_{x}CoSi_{3}","The results of electrical resistivity, heat capacity and magnetic susceptibility behavior of new class of alloys, Ce_{2-x}La_{x}CoSi_{3}, are reported. The x= 0.0 alloy is mixed valent and La substitution for Ce (x= 0.25) induces linear temperature dependence of resistivity at low temperatures, an observation of relevance to the topic of non-Fermi liquid behavior. The modifications of Kondo effect for all the alloys are also presented.",9902298v1 2000-09-14,c(2x2) Interface Alloys in Co/Cu Multilayers - Influence on Interlayer Exchange Coupling and GMR,"The influence of a c(2x2) ordered interface alloy of 3d transition metals at the ferromagnet/nonmagnet interface on interlayer exchange coupling (IXC), the formation of quantum well states (QWS) and the phenomenon of Giant MagnetoResistance is investigated. We obtained a strong dependence of IXC on interface alloy formation. The GMR ratio is also strongly influenced. We found that Fe, Ni and Cu alloys at the interface enhance the GMR ratio for in-plane geometry by nearly a factor of 2.",0009213v2 2001-03-23,On the de Haas-van Alphen effect in inhomogeneous alloys,"We show that Landau level broadening in alloys occurs naturally as a consequence of random variations in the local quasiparticle density, without the need to consider a relaxation time. This approach predicts Lorentzian-broadened Landau levels similar to those derived by Dingle using the relaxation-time approximation. However, rather than being determined by a finite relaxation time $\tau$, the Landau-level widths instead depend directly on the rate at which the de Haas-van Alphen frequency changes with alloy composition. The results are in good agreement with recent data from three very different alloy systems.",0103476v1 2001-12-19,Interesting magnetic properties of Fe$_{1-x}$Co$_x$Si alloys,"Solid solution between nonmagnetic narrow gap semiconductor FeSi and diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with long-range helical magnetic ordering, for a wide range of intermediate concentration. We report various interesting magnetic properties of these alloys, including low temperature re-entrant spin-glass like behaviour and a novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya interaction in the magnetic response of these non-centrosymmetric alloys is discussed.",0112346v1 2004-03-10,Monte Carlo Simulation of Surface De-alloying of Au/Ni(110),"Based on BFS model and using Monte Carlo simulation we confirms the de-alloying in immiscible Au/Ni(110) system, and the critical Au coverage when de-alloying happens is also consistent with experiments. At the same time our simulation show that the structural phase transition will lead to the saturation of the number of alloying Au atoms.",0403259v2 2004-06-21,Two-Phase Equilibrium in Small Alloy Particles,"The coexistence of two phases within a particle requires an interface with a significant capillary energy. We show that this entails changes in the nature of alloy phase equilibria at small size. Most notably, the eutectic points in alloy phase diagrams degenerate into intervals of composition where the alloy melts discontinuously.",0406477v2 2004-08-27,Tunable magnetization damping in transition metal ternary alloys,"We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be enhanced sufficiently to reduce post-switching magnetization precession to an acceptable level by alloying with the transition metal osmium (Os). The damping increases monotonically upon raising the Os-concentration in Py, at least up to 9% of Os. Other effects of alloying with Os are suppression of magnetization and enhancement of in-plane anisotropy. Magnetization damping also increases significantly upon alloying with the five other transition metals included in this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly as with Os.",0408608v1 2004-11-06,Curie temperature and quantum phase transitions in the Hubbard model with binary alloy disorder,"Magnetic and electric properties of the Hubbard model with binary alloy disorder are studied within the dynamical mean--field theory. A paramagnet--ferromagnet phase transition and a Mott--Hubbard metal--insulator transition are observed upon varying the alloy concentration. A disorder induced enhancement of the Curie temperature is demonstrated and explained by the effects of band splitting and subband filling. Different quantum phase transitions driven by changes of the alloy concentration are identified.",0411168v1 2006-11-26,Critical cooling rate for the glass formation of ferromagnetic Fe40Ni40P14B6 alloy,"Bulk ferromagnetic amorphous Fe-Ni-P-B alloys in rod shape were formed by a rapid solidification technique. The largest amorphous specimen prepared had a diameter of ~2.5 mm and the corresponding cooling rate for the glass formation of this alloy system in our experiment can be estimate to be around 492.4 K/s by the method of finite-difference numerical calculation. This value is on the same order of magnitude as the critical cooling rate Rc of Fe40Ni40P14B6 alloy estimated by the method of constructing the continuous-cooling-transformation (CCT) curve. It is indicated that the heterophase impurities have been eliminated well in our experiment.",0611651v2 2006-12-14,Magnetic order of FeMn alloy on the W(001) surface,"We investigate theoretically the ground state of the FeMn binary alloy monolayer on the W(001) surface, the stability of different magnetic configurations (ferro/antiferromagnetic, disordered local moments, etc.) and estimate concentrations at which a transition occurs between different magnetic orders. The tight-binding linear muffin-tin orbital method combined with the coherent potential approximation is used to treat the surface alloy appropriately. We discuss the role of disorder on the phase transitions in surface alloys composed from two different 3d transition metals.",0612366v1 2007-01-26,X-Ray diffraction studies on asymmetrically broadened peaks of heavily deformed Zirconium based alloys,"The diffraction peaks of Zircaloy-2 and Zr-2.5%Nb alloys at various deformations are found to be asymmetric in nature. In order to characterize the microstructure from these asymmetric peaks of these deformed alloys, X-Ray Diffraction Line Profile Analysis like Williamson-Hall technique, Variance method based on second and fourth order restricted moments and Stephens model based on anisotropic strain distribution have been adopted. The domain size and dislocation density have been evaluated as a function of deformation for both these alloys. These techniques are useful where the dislocation structure is highly inhomogeneous inside the matrix causing asymmetry in the line profile, particularly for deformed polycrystalline materials.",0701645v1 1995-02-22,Static displacements and chemical correlations in alloys,"Recent experiments in metallic solid solutions have revealed interesting correlations between static pair-displacements and the ordering behavior of these alloys. This paper discusses a simple theoretical model which successfully explains these observations and which provides a natural framework for analyzing experimental measurements of pair-displacements and chemical correlations in solid solutions. The utility and scope of this model is demonstrated by analyzing results of experiments on $Ni-Fe$ and $Cr-Fe$ alloys and results of simulations of $Cu-Au$ and $Cu-Ag$ alloys.",9502005v1 2007-04-16,Classical nucleation theory in ordering alloys precipitating with L12 structure,"By means of low-temperature expansions (LTEs), the nucleation free energy and the precipitate interface free energy are expressed as functions of the solubility limit for alloys which lead to the precipitation of a stoichiometric L12 compound such as Al-Sc or Al-Zr alloys. Classical nucleation theory is then used to obtain a simple expression of the nucleation rate whose validity is demonstrated by a comparison with atomic simulations. LTEs also explain why simple mean-field approximation like the Bragg-Williams approximation fails to predict correct nucleation rates in such an ordering alloy.",0704.1988v1 2008-12-17,Jahn-Teller like origin of the tetragonal distortion in disordered Fe-Pd magnetic shape memory alloys,"The electronic structure and magnetic properties of disordered Fe$_{x}$Pd$_{100-x}$ alloys $(50 < x < 85)$ are investigated in the framework of density functional theory using the full potential local orbital method (FPLO). Disorder is treated in the coherent potential approximation (CPA). Our calculations explain the experimental magnetization data. The origin of the tetragonal distortion in the Fe-Pd magnetic shape memory alloys is found to be a Jahn-Teller like effect which allows the system to reduce its band energy in a narrow composition range. Prospects for an optimization of the alloys' properties by adding third elements are discussed.",0812.3332v1 2011-04-08,Diameter dependence of SiGe nanowire thermal conductivity,"We theoretically compute the thermal conductivity of SiGe alloy nanowires as a function of nanowire diameter, alloy concentration, and temperature, obtaining a satisfactory quantitative agreement with experimental results. Our results account for the weaker diameter dependence of the thermal conductivity recently observed in Si$_{1-x}$Ge$_x$ nanowires ($x<0.1$), as compared to pure Si nanowires. We also present calculations in the full range of alloy concentrations, $0 \leq x \leq 1$, which may serve as a basis for comparison with future experiments on high alloy concentration nanowires.",1104.1570v1 2012-01-19,Phase transformation in steel alloys for magnetocaloric applications; Fe$_{85-x}$Cr$_{15}$Ni$_{x}$ and Fe$_{85-x}$Cr$_{15}$Mn$_{x}$ as prototypes,"We here show by first principles theory that it is possible to achieve a structural and magnetic phase transition in common steel alloys like Fe$_{85}$Cr$_{15}$, by alloying with Ni or Mn. The predicted phase transition is from the ferromagnetic body centered cubic (bcc) phase to the paramagnetic face centered cubic (fcc) phase. The relatively high average magnetic moment of $\sim1.4\mu_{B}$/atom predicted at the transition suggests that stainless steel potentially can present a magnetocaloric effect strong enough to make these alloys good candidates for refrigeration applications operating at and around room temperature.",1201.4176v1 2014-04-03,Magnetic and Thermodynamic properties of face-centered cubic Fe-Ni alloys,"A model lattice ab initio parameterised Hamiltonian spanning a broad range of alloy compositions and a large variety of chemical and magnetic configurations has been developed for face-centered cubic Fe-Ni alloys. Thermodynamic and magnetic properties of the alloys are explored using configuration and magnetic Monte Carlo simulations in a temperature range extending well over 1000 K.",1404.0888v1 2015-12-20,"Structure, elastic and bonding properties of hcp ZrxTi1-x binary alloy from first-principles calculations","First principles calculations were performed to study the structural, elastic, and bonding properties of hcp ZrxTi1-x binary alloy. The special quasi- random structure (SQS) method is employed to mimic the random hcp ZrxTi1-x alloy. It is found that Bulk modulus, B, Young's modulus, E, and shear modulus, G, exhibit decreasing trends as increasing the amount of Zr. A ductile behavior ZrxTi1-x is predicted in the whole composition range. In terms of Mulliken charge analisis, we found that the element Ti behaves much more electronegative than Zr in hcp ZrxTi1-x alloy, and the charge transfer of an atom is approximately linear to the amount of other element atom surrounding it.",1512.06408v1 2016-04-28,Utilization of mechanical alloying method for flux growth of single crystalline BaFe$_2$(As$_{1-x}$P$_x$)$_2$,"Mechanical alloying method has been employed to prepare the Ba-Fe-As-P precursors, necessary for the Ba-(As,P) flux growth of the single crystalline BaFe$_2$(As$_{1-x}$P$_x$)$_2$. By alloying constituent elementals mechanically, the Ba-(As,P) precursors are successfully formed at the room temperature within one hour, significantly reducing preparation time. Using the mechanically alloyed precursors, we have grown single crystals of BaFe$_2$(As$_{1-x}$P$_x$)$_2$ with the sizes up to 5~mm $\times$ 5~mm $\times$ 0.1~mm.",1604.08375v1 2017-08-25,Phase partitioning in a novel near equi-atomic AlCuFeMn alloy,"A novel low cost, near equi-atomic alloy comprising of Al, Cu, Fe and Mn is synthesized using arc-melting technique. The cast alloy possesses a dendritic microstructure where the dendrites consist of disordered FCC and ordered FCC phases. The inter-dendritic region is comprised of ordered FCC phase and spinodally decomposed BCC phases. A Cu segregation is observed in the inter-dendritic region while dendritic region is rich in Fe. The bulk hardness of the alloy is ~ 380 HV, indicating significant yield strength.",1708.07688v1 2018-03-02,Probabilistic design of a molybdenum-base alloy using a neural network,"An artificial intelligence tool is exploited to discover and characterize a new molybdenum-base alloy that is the most likely to simultaneously satisfy targets of cost, phase stability, precipitate content, yield stress, and hardness. Experimental testing demonstrates that the proposed alloy fulfils the computational predictions, and furthermore the physical properties exceed those of other commercially available Mo-base alloys for forging-die applications.",1803.00879v1 2017-04-06,Thermoelectric power factor of Bi-Sb-Te and Bi-Te-Se alloys and doping strategy: First-principles study,"By performing first principles calculations combined with Boltzmann transport equations, we calculate the thermoelectric power factor (PF) of Bi-Sb-Te and Bi-Te-Se ternary alloys as a function of alloy composition ratio, carrier concentration, and temperature. The point defect formation energy calculations also perform to search potential n-type dopant candidates in ternaries.",1704.01723v1 2018-10-09,Peculiar spectra of dark and bright excitons in alloyed nanowire quantum dots,"Excitons in alloyed nanowire quantum dots have unique spectra as shown here using atomistic calculations. The bright exciton splitting is triggered solely by alloying and despite cylindrical quantum dot shape reaches over $15~\mu$eV, contrary to previous theoretical predictions, however, in line with experimental data. This splitting can however be tuned by electric field to go below $1$~$\mu$eV threshold. The dark exciton optical activity is also strongly affected by alloying reaching notable $1/3500$ fraction of the bright exciton and having large out-of-plane polarized component.",1810.03831v1 2018-10-24,High Strain Rate Behaviour of Nano-quasicrystalline Al93Fe3Cr2Ti2 Alloy and Composites,"In the present work, we demonstrate for the first time the outstanding dynamic mechanical properties of nano-quasicrystalline Al93Fe3Cr2Ti2 at.% alloy and composites. Unlike most crystalline aluminium-based alloys, this alloy and composites exhibit substantial strain rate sensitivity and retain much of their ductility at high rates of strain. This opens new pathways for use in safety-critical materials where impact resistance is required.",1810.10476v2 2019-04-05,New high-entropy alloy superconductor Hf$_{21}$Nb$_{25}$Ti$_{15}$V$_{15}$Zr$_{24}$,"High-entropy alloys are a new class of alloys, and attract much attention due to their unique properties. Since the discovery of a superconducting high-entropy alloy (HEA) in 2014, the materials research on HEA superconductor is a hot topic. We have found that Hf$_{21}$Nb$_{25}$Ti$_{15}$V$_{15}$Zr$_{24}$ body-centered-cubic (BCC) HEA is a new superconductor with the superconducting critical temperature Tc of 5.3 K. We briefly discussed the comparison of cocktail effect of Tc among BCC HEA superconductors.",1904.03291v1 2019-04-10,Enhancement of spin transparency by interfacial alloying,"We report that atomic-layer alloying (intermixing) at a Pt/Co interface can increase, by approximately 30%, rather than degrade the interfacial spin transparency, and thereby strengthen the efficiency of the dampinglike spin-orbit torque arising from the spin Hall effect in the Pt. At the same time, this interfacial alloying substantially reduces fieldlike spin-orbit torque. Insertion of an ultrathin magnetic alloy layer at heavy-metal/ferromagnet interfaces represents an effective approach for improving interfacial spin transparency that may enhance not only spin-orbit torques but also the spin detection efficiency in inverse spin Hall experiments.",1904.05455v1 2019-07-03,Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the form of AB$_p$C$_{1-p}$,"Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the form of AB$_p$C$_{1-p}$, especially. The effect of Hamiltonian parameters on the dynamic magnetic features of the system are investigated. For this aim, an AB$_p$C$_{1-p}$ ternary alloy system was simulated within the mean-field approximation based on a Glauber type stochastic dynamic and for simplicity, A, B and C ions as SA = 1/2, SB = 1 and SC = 3/2, were chosen respectively. It was found that in our dynamic system the critical temperature was always dependent on the concentration ratio of the ternary alloy.",1907.01850v1 2019-10-29,Improvement in corrosion resistance and biocompatibility of AZ31 magnesium alloy by NH+2 ions,"Magnesium alloys have been considered to be favorable biodegradable metallic materials used in orthopedic and cardiovascular applications. We introduce NH+2 to the AZ31 Mg alloy surface by ion implantation at the energy of 50 KeV with doses ranging from 1e16 ions/cm2 to 1e17 ions/cm2 to improve its corrosion resistance and biocompatibility. Surface morphology, mechanical properties, corrosion behavior and biocompatibility are studied in the experiments. The analysis confirms that the modified surface with smoothness and hydrophobicity significantly improves the corrosion resistance and biocompatibility while maintaining the mechanical property of the alloy.",1910.13265v1 2012-09-04,Rapid Production of Accurate Embedded-Atom Method Potentials for Metal Alloys,"The most critical limitation to the wide-scale use of classical molecular dynamics for alloy design is the availability of suitable interatomic potentials. In this work, we demonstrate a simple procedure to generate a library of accurate binary potentials using already-existing single-element potentials that can be easily combined to form multi-component alloy potentials. For the Al-Ni, Cu-Au, and Cu-Al-Zr systems, we show that this method produces results comparable in accuracy to alloy potentials where all parts have been fitted simultaneously, without the additional computational expense. Furthermore, we demonstrate applicability to both crystalline and amorphous phases.",1209.0619v1 2020-08-07,Vibrational Entropy Investigation in High Entropy Alloys,"The lattice dynamics for NiCo, NiFe, NiFeCo, NiFeCoCr, and NiFeCoCrMn medium to high entropy alloy have been investigated using the DFT calculation. The phonon dispersions along three different symmetry directions are calculated by the weighted dynamical matrix (WDM) approach and compared with the supercell approach and inelastic neutron scattering. We could correctly predict the trend of increasing of the vibrational entropy by adding the alloys and the highest vibrational entropy in NiFeCoCrMn high entropy alloy by WDM approach. The averaged first nearest neighbor (1NN) force constants between various pairs of atoms in these intermetallic are obtained from the WDM approach. The results are discussed based on the analysis of these data.",2008.03338v2 2016-03-11,Alloy meets TLA+: An exploratory study,"Alloy and TLA+ are two formal specification languages that are increasingly popular due to their simplicity and flexibility, as well as the effectiveness of their companion model checkers, the Alloy Analyzer and TLC, respectively. Nonetheless, while TLA+ focuses on temporal properties, Alloy is better suited to handle structural properties, requiring ad hoc mechanisms to reason about temporal properties. Thus, both have limitations in the specification and analysis of systems rich in both static and dynamic properties. This paper explores the pros and cons of these two frameworks when handling this class of systems through the step-by-step modeling, specification and verification of an example.",1603.03599v1 2019-05-13,Application of the Statistical Moment Method to Melting Properties of Ternary Alloys with FCC Structure,"The high-pressure melting properties of the ternary alloy AlCuSi with face-centred cubic structure is theoretically investigated using the statistical moment method. We calculate the melting temperature for the alloy under pressure up to 80 GPa. The dependence of the melting temperature on the content of alloying elements is also studied. Our results agree well with previous experiments, simulations, and other theoretical calculations.",1905.05047v2 2020-09-24,Correlation of microdistortions with misfit volumes in High Entropy Alloys,"The yield strengths of High Entropy Alloys have recently been correlated with measured picometer-scale atomic distortions. Here, the root mean square microdistortion in a multicomponent alloy is shown to be nearly proportional to the misfit-volume parameter that enters into a predictive model of solute strengthening. Analysis of two model ternary alloy families, face-centered cubic Cr-Fe-Ni and body-centered cubic Nb-Mo-V, demonstrates the correlation over a wide composition space. The reported correlation of yield strength with microdistortion is thus a consequence of the correlation between microdistortion and misfit parameter and the derived dependence of yield strength on the misfit parameter.",2009.11695v1 2020-11-24,Phase Diagrams of Generalized Spin-S Magnetic Binary Alloys,"Critical properties of the generalized spin-S magnetic binary alloys represented by $A_{c}B_{1-c}$ have been investigated within the framework of EFT. By inspecting the evolution of the phase diagrams with the concentration for several spin values, general results have been obtained. Obtained results cover the results obtained for special cases in the literature. Type of the transition (first/second order), as well as the presence of the tricritical point have been determined for general spin models. It has also been shown that, the same critical concentration value exist in the system, regardless of the spin value for binary alloy consist of half integer-integer spin alloy.",2011.12330v1 2020-12-20,Precipitate strengthening of pyramidal slip in Mg-Zn alloys,"The mechanical properties of Mg-4wt.% Zn alloy single crystals along the [0001] orientation were measured through micropillar compression at 23C and 100C. Basal slip was dominant in the solution treated alloy, while pyramidal slip occurred in the precipitation hardened alloy. Pyramidal dislocations pass the precipitates by forming Orowan loops, leading to homogeneous deformation and to a strong hardening. The predictions of the yield stress based on the Orowan model were in reasonable agreement with the experimental data. The presence of rod-shape precipitates perpendicular to the basal plane leads to a strong reduction in the plastic anisotropy of Mg.",2012.10886v1 2021-02-03,Predicting grain boundary energies of complex alloys from ab initio calculations,"Investigating the grain boundary energies of pure fcc metals and their surface energies obtained from ab initio modeling, we introduce a robust method to estimate the grain boundary energies for complex multicomponent alloys. The input parameter is the surface energy of the alloy, which can easily be accessed by modern ab initio calculations based on density functional theory. The method is demonstrated in the case of paramagnetic Fe-Cr-Ni alloys for which reliable grain boundary data is available.",2102.01972v1 2021-10-21,"Efficient, Systematic Estimation of Alloy Free Energy from Special Microscopic States","For classical discrete systems under constant composition typically refferred to substitutional alloys, we propose calculation method of Helmholtz free energy based on a set of special microscopic states. The advantage of the method is that configuration of the special states are essentially independent of energy and temperature, and they depend only on underlying lattice: The special states can be known a priori without any thermodynamic information, enabling systematic prediction of free energy for multicomponent alloys. We confirm that by comparing to conventional thermodynamic simulation, information about the special states provide reasonable predictive power above order-disorder and phase-separating transition temperature for alloys with many-body (up to 3-body) interactions.",2110.10839v1 2021-12-24,Analysis of Raman and Ellipsometric Responses of Nb$_{x}$W$_{1-x}$Se$_{2}$ alloys,"The growth of transition metal dichalcogenide (TMDC) alloys provides an opportunity to experimentally access information elucidating how optical properties change with gradual substitutions in the lattice compared with their pure compositions. In this work, we performed growths of alloyed crystals with stoichiometric compositions between pure forms of NbSe2 and WSe2, followed by an optical analysis of those alloys by utilizing Raman spectroscopy and spectroscopic ellipsometry.",2112.13063v1 2023-01-23,Superconductivity in the Face Centered Cubic $\rm W_{n-x}Mo_{x}RhIrPt_{2}$ High Entropy Alloy,"We report single phase superconducting face centered cubic (FCC) intermetallic high entropy alloys (HEAs) synthesized via splat cooling. The single phase materials fall at electron counts in the HEA superconductor alloy family where structural stability and optimal superconducting electron counts clash. The materials' superconducting properties follow the general trends published for metallic alloys. Many of the superconducting characteristics are summarized. Insights are provided as to why an FCC structure may be stable.",2301.09678v2 2006-01-30,Correlation in the transition metal based Heusler compounds Co$_2$MnSi and Co$_2$FeSi,"Half-metallic ferromagnets like the full Heusler compounds with formula X$_2$YZ are supposed to show an integer value of the spin magnetic moment. Calculations reveal in certain cases of X = Co based compounds non-integer values, in contrast to experiments. In order to explain deviations of the magnetic moment calculated for such compounds, the dependency of the electronic structure on the lattice parameter was studied theoretically. In local density approximation (LDA), the minimum total energy of Co$_2$FeSi is found for the experimental lattice parameter, but the calculated magnetic moment is about 12% too low. Half-metallic ferromagnetism and a magnetic moment equal to the experimental value of $6\mu_B$ are found, however, only after increasing the lattice parameter by more than 6%. To overcome this discrepancy, the LDA$+U$ scheme was used to respect on-site electron correlation in the calculations. Those calculations revealed for Co$_2$FeSi that an effective Coulomb-exchange interaction $U_{eff}=U-J$ in the range of about 2eV to 5eV leads to half-metallic ferromagnetism and the measured, integer magnetic moment at the measured lattice parameter. Finally, it is shown in the case of Co$_2$MnSi that correlation may also serve to destroy the half-metallic behavior if it becomes too strong (for Co$_2$MnSi above 2eV and for Co$_2$FeSi above 5eV). These findings indicate that on-site correlation may play an important role in the description of Heusler compounds with localized moments.",0601671v1 2007-10-30,Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds,"The XYZ half-Heusler crystal structure can conveniently be described as a tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X species. This description is well suited to understand the electronic structure of semiconducting 8-electron compounds such as LiAlSi (formulated Li$^+$[AlSi]$^-$) or semiconducting 18-electron compounds such as TiCoSb (formulated Ti$^{4+}$[CoSb]$^{4-}$). The basis for this is that [AlSi]$^-$ (with the same electron count as Si$_2$) and [CoSb]$^{4-}$ (the same electron count as GaSb), are both structurally and electronically, zinc-blende semiconductors. The electronic structure of half-metallic ferromagnets in this structure type can then be described as semiconductors with stuffing magnetic ions which have a local moment: For example, 22 electron MnNiSb can be written Mn$^{3+}$[NiSb]$^{3-}$. The tendency in the 18 electron compound for a semiconducting gap -- believed to arise from strong covalency -- is carried over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly propose the systematic examination of 18-electron hexagonal compounds for semiconducting gaps; these would be the ""stuffed wurtzite"" analogues of the ""stuffed zinc blende"" half-Heusler compounds. These semiconductors could then serve as the basis for possibly new families of half-metallic compounds, attained through appropriate replacement of non-magnetic ions by magnetic ones. These semiconductors and semimetals with tunable charge carrier concentrations could also be interesting in the context of magnetoresistive and thermoelectric materials.",0710.5769v1 2013-11-20,Nuclear magnetic resonance study of thin Co$_2$FeAl$_{0.5}$Si$_{0.5}$ Heusler films with varying thickness,"Type, degree and evolution of structural order are important aspects for understanding and controlling the properties of highly spin polarized Heusler compounds, in particular with respect to the optimal film growth procedure. In this work, we compare the structural order and the local magnetic properties revealed by nuclear magnetic resonance (NMR) spectroscopy with the macroscopic properties of thin Co$_2$FeAl$_{0.5}$Si$_{0.5}$ Heusler films with varying thickness. A detailed analysis of the measured NMR spectra presented in this paper enables us to find a very high degree of $L2_1$ type ordering up to 81% concomitantly with excess Fe of 8 to 13% at the expense of Al and Si. We show, that the formation of certain types of order do not only depend on the thermodynamic phase diagrams as in bulk samples, but that the kinetic control may contribute to the phase formation in thin films. It is an exciting finding that Co$_2$FeAl$_{0.5}$Si$_{0.5}$ can form an almost ideal $L2_1$ structure in films though with a considerable amount of Fe-Al/Si off-stoichiometry. Moreover, the very good quality of the films as demonstrated by our NMR study suggests that the novel technique of off-axis sputtering technique used to grow the films sets stage for the optimized performance of Co$_2$FeAl$_{0.5}$Si$_{0.5}$ in spintronic devices.",1311.5070v2 2015-11-09,NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds,"Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by 209Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states.",1511.02706v2 2016-08-09,Compensated ferrimagnetic tetragonal Heusler thin films for antiferromagnetic spintronics,"In recent years, antiferromagnetic spintronics has received much attention since ideal antiferromagnets do not produce stray fields and are much more stable to external magnetic fields compared to materials with net magnetization. Akin to antiferromagnets, compensated ferrimagnets have zero net magnetization but have the potential for large spin-polarization and strong out of plane magnetic anisotropy, and, hence, are ideal candidates for high density memory applications. Here, we demonstrate that a fully compensated magnetic state with a tunable magnetic anisotropy is realized in Mn-Pt-Ga based tetragonal Heusler thin films. Furthermore, we show that a bilayer formed from a fully compensated and a partially compensated Mn-Pt-Ga layer, exhibits a large interfacial exchange bias up to room temperature. The present work establishes a novel design principle for spintronic devices that are formed from materials with similar elemental compositions and nearly identical crystal and electronic structures. Such devices are of significant practical value due to their improved properties such as thermal stability. The flexible nature of Heusler materials to achieve tunable magnetizations, and anisotropies within closely matched materials provides a new direction to the growing field of antiferromagnetic spintronics.",1608.02887v1 2017-07-03,Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes,"Spin caloritronics studies the interplay between charge-, heat- and spin-currents, which are initiated by temperature gradients in magnetic nanostructures. A plethora of new phenomena has been discovered that promises, e.g., to make wasted heat in electronic devices useable or to provide new read-out mechanisms for information. However, only few materials have been studied so far with Seebeck voltages of only some {\mu}V, which hampers applications. Here, we demonstrate that half-metallic Heusler compounds are hot candidates for enhancing spin-dependent thermoelectric effects. This becomes evident when considering the asymmetry of the spin-split density of electronic states around the Fermi level that determines the spin-dependent thermoelectric transport in magnetic tunnel junctions. We identify Co$_2$FeAl and Co$_2$FeSi Heusler compounds as ideal due to their energy gaps in the minority density of states, and demonstrate devices with substantially larger Seebeck voltages and tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B based junctions.",1707.00505v2 2018-09-20,Surface Majorana Flat Bands in $j=\frac{3}{2}$ Superconductors with Singlet-Quintet Mixing,"Recent experiments have revealed the evidence of nodal-line superconductivity in half-Heusler superconductors, e.g. YPtBi. Theories have suggested the topological nature of such nodal-line superconductivity and proposed the existence of surface Majorana flat bands on the (111) surface of half-Heusler superconductors. Due to the divergent density of states of the surface Majorana flat bands, the surface order parameter and the surface impurity play essential roles in determining the surface properties. In this work, we studied the effect of the surface order parameter and the surface impurity on the surface Majorana flat bands of half-Heusler superconductors based on the Luttinger model. To be specific, we consider the topological nodal-line superconducting phase induced by the singlet-quintet pairing mixing, classify all the possible translationally invariant order parameters for the surface states according to irreducible representations of $C_{3v}$ point group, and demonstrate that any energetically favorable order parameter needs to break time-reversal symmetry. We further discuss the energy splitting in the energy spectrum of surface Majorana flat bands induced by different order parameters and non-magnetic or magnetic impurities. We proposed that the splitting in the energy spectrum can serve as the fingerprint of the pairing symmetry and mean-field order parameters. Our theoretical prediction can be examined in the future scanning tunneling microscopy experiments.",1809.07455v2 2021-07-10,Anisotropic exchange and non-collinear antiferromagnets on a noncentrosymmetric fcc structure as in the half-Heuslers,"One of the signatures of the face-centered cubic (fcc) antiferromagnet as a typical example of a geometrically frustrated system is the large ground state degeneracy of the classical nearest neighbor and next-nearest neighbor Heisenberg (isotropic) model on this lattice. In particular, collinear states are degenerate with non-collinear and non-coplanar ones: this degeneracy is accidental and is expected to be lifted by anisotropic exchange interactions. In this work, we derive the most general nearest and next-nearest neighbor exchange model allowed by the space-group symmetry of the noncentrosymmetric half-Heusler compounds, which includes three anisotropic terms: the so-called Kitaev, Gamma and Dzyaloshinskii-Moriya interactions -- most notably, the latter is allowed by the breaking of inversion symmetry in these materials and has not been previously been studied in the context of the fcc lattice. We compute the resulting phase diagram and show how the different terms lift the ground state degeneracy of the isotropic model, and lay emphasis on finding regimes where multi-q (non-collinear/non-coplanar) states are selected by anisotropy. We then discuss the role of quantum fluctuations and the coupling to a magnetic field in the ground state selection, and show that these effects can stabilize non-coplanar (triple-q) states. These results suggest that some half-Heusler antiferromagnets might host rare non-collinear/non-coplanar orders, which may in turn explain the unusual transport properties detected in these semimetals.",2107.04906v2 2017-06-11,First principles study of the structural phase stability and magnetic order in various structural phases of Mn$_2$FeGa,"We investigate the structural and magnetic properties of Mn$_{2}$FeGa for different phases(cubic, hexagonal and tetragonal) reported experimentally using density functional theory. The relative structural stabilities, and the possible phase transformation mechanisms are discussed using results for total energy, electronic structure and elastic constants. We find that the phase transformation form hexagonal to ground state tetragonal structure would take place through a Heusler-like phase which has a pronounced electronic instability. The electronic structures, the elastic constants and the supplementary phonon dispersions indicate that the transition from the Heusler-like to the tetragonal phase is of pure Jahn-Teller origin. We also describe the ground state magentic structures in each phase by computations of the exchange interactions. For Heusler-like and tetragonal phases, the ferromagnetic exchange interactions associated with the Fe atoms balance the dominating antiferromagnetic interactions between the Mn atoms leading to collinear magnetic structures. In the hexagonal phase, the direction of atomic moment are completely in the planes with a collinear like structure, in stark contrast to the well known non-collinear magnetic structure in the hexagonal phase of Mn$_{3}$Ga, another material with similar structural properties. The overwhelmingly large exchange interactions of Fe with other magnetic atoms destroy the possibility of magnetic frustration in the hexagonal phase of Mn$_{2}$FeGa. This comprehensive study provides significant insights into the microscopic physics associated with the structural and magnetic orders in this compound.",1706.03425v1 2019-05-22,Ultra-low magnetic damping in Co 2 Mn-based Heusler compounds: promising materials for spintronic,"The prediction of ultra-low magnetic damping in Co 2 MnZ Heusler half-metal thin-film magnets is explored in this study and the damping response is shown to be linked to the underlying electronic properties. By substituting the Z elements in high crystalline quality films (Co 2 MnZ with Z=Si, Ge, Sn, Al, Ga, Sb), electronic properties such as the minority spin band gap, Fermi energy position in the gap and spin polarization can be tuned and the consequence on magnetization dynamics analyzed. The experimental results allow us to directly explore the interplay of spin polarization, spin gap, Fermi energy position and the magnetic damping obtained in these films, together with ab initio calculation predictions. The ultra-low magnetic damping coefficients measured in the range 4.1 10-4-9 10-4 for Co 2 MnSi, Ge, Sn, Sb are the lowest values obtained on a conductive layer and offers a clear experimental demonstration of theoretical predictions on Half-Metal Magnetic Heusler compounds and a pathway for future materials design.",1905.08987v1 2020-02-07,"Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization","Engineering of magnetic materials for developing better spintronic applications relies on the control of two key parameters: the spin polarization and the Gilbert damping responsible for the spin angular momentum dissipation. Both of them are expected to affect the ultrafast magnetization dynamics occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x Heusler compounds to adjust the degree of spin polarization P from 60 to 100% and investigate how it correlates with the damping. We demonstrate experimentally that the damping decreases when increasing the spin polarization from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of 4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the relation between these two parameters and the ultrafast demagnetization time characterizing the loss of magnetization occurring after femtosecond laser pulse excitation. The demagnetization time is observed to be inversely proportional to 1-P and as a consequence to the magnetic damping, which can be attributed to the similarity of the spin angular momentum dissipation processes responsible for these two effects. Altogether, our high quality Heusler compounds allow controlling the band structure and therefore the channel for spin angular momentum dissipation.",2002.02686v1 2020-03-12,Semi-adsorption-controlled growth window for half Heusler FeVSb epitaxial films,"The electronic, magnetic, thermoelectric, and topological properties of Heusler compounds (composition $XYZ$ or $X_2 YZ$) are highly sensitive to stoichiometry and defects. Here we establish the existence and experimentally map the bounds of a \textit{semi} adsorption-controlled growth window for semiconducting half Heusler FeVSb films, grown by molecular beam epitaxy (MBE). We show that due to the high volatility of Sb, the Sb stoichiometry is self-limiting for a finite range of growth temperatures and Sb fluxes, similar to the growth of III-V semiconductors such as GaSb and GaAs. Films grown within this window are nearly structurally indistinguishable by X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). The highest electron mobility and lowest background carrier density are obtained towards the Sb-rich bound of the window, suggesting that Sb-vacancies may be a common defect. Similar \textit{semi} adsorption-controlled bounds are expected for other ternary intermetallics that contain a volatile species $Z=$\{Sb, As, Bi\}, e.g., CoTiSb, LuPtSb, GdPtBi, and NiMnSb. However, outstanding challenges remain in controlling the remaining Fe/V ($X/Y$) transition metal stoichiometry.",2003.05971v2 2020-03-21,Scaling of quadratic and linear magnetooptic Kerr effect spectra with L2$_1$ ordering of Co$_2$MnSi Heusler compound,"The Heusler compound Co$_2$MnSi provides a crystallographic transition from B2 to L2$_1$ structure with increasing annealing temperature $T_a$, being a model system for investigating the influence of crystallographic ordering on structural, magnetic, optic, and magnetooptic (MO) properties. Here, we present quadratic magnetooptic Kerr effect (QMOKE) spectra depending on $M^2$ in addition to the linear magnetooptic Kerr effect (LinMOKE) spectra being proportional to $M$, both in the extended visible spectral range of light from 0.8\,eV to 5.5\,eV. We investigated a set of Co$_2$MnSi thin films deposited on MgO(001) substrates and annealed from 300$^\circ$C to 500$^\circ$C. The amplitude of LinMOKE and QMOKE spectra scales linearly with $T_a$, and this effect is well pronounced at the resonant peaks below 2.0\,eV of the QMOKE spectra. Furthermore, the spectra of the MO parameters, which fully describe the MO response of Co$_2$MnSi up to the second order in $M$, are obtained dependend on $T_a$. Finally, the spectra are compared to ab-initio calculations of a purely L2$_1$ ordered Co$_2$MnSi Heusler compound.",2003.09728v2 2020-03-25,Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materials,"Chemical doping is one of the most important strategies for tuning electrical properties of semiconductors, particularly thermoelectric materials. Generally, the main role of chemical doping lies in optimizing the carrier concentration, but there can potentially be other important effects. Here, we show that chemical doping plays multiple roles for both electron and phonon transport properties in half-Heusler thermoelectric materials. With ZrNiSn-based half-Heusler materials as an example, we use high-quality single and polycrystalline crystals, various probes, including electrical transport measurements, inelastic neutron scattering measurement, and first-principles calculations, to investigate the underlying electron-phonon interaction. We find that chemical doping brings strong screening effects to ionized impurities, grain boundary, and polar optical phonon scattering, but has negligible influence on lattice thermal conductivity. Furthermore, it is possible to establish a carrier scattering phase diagram, which can be used to select reasonable strategies for optimization of the thermoelectric performance.",2003.11222v3 2020-06-03,Half-Heusler thermoelectric materials: NMR studies,"We report $^{59}$Co, $^{93}$Nb, and $^{121}$Sb nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations on a series of half-Heusler semiconductors, including NbCoSn, ZrCoSb, TaFeSb and NbFeSb, to better understand their electronic properties and general composition-dependent trends. These materials are of interest as potentially high efficiency thermoelectric materials. Compared to the other materials, we find that ZrCoSb tends to have a relatively large amount of local disorder, apparently antisite defects. This contributes to a small excitation gap corresponding to an impurity band near the band edge. In NbCoSn and TaFeSb, Curie-Weiss-type behavior is revealed, which indicates a small density of interacting paramagnetic defects. Very large paramagnetic chemical shifts are observed associated with a Van Vleck mechanism due to closely spaced $d$ bands splitting between the conduction and valence bands. Meanwhile, DFT methods were generally successful in reproducing the chemical shift trend for these half-Heusler materials, and we identify an enhancement of the larger-magnitude shifts, which we connect to electron interaction effects. The general trend is connected to changes in $d$-electron hybridization across the series.",2006.02013v1 2020-06-17,"Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes","Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al$_2$O$_3$ substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetixm and magnetostriction) and strain gradients (flexomagnetism).",2006.10100v3 2020-11-06,Thermoelectric power factor under strain-induced band-alignment in the half-Heuslers NbCoSn and TiCoSb,"Band convergence is an effective strategy to improve the thermoelectric performance of complex bandstructure thermoelectric materials. Half-Heuslers are good candidates for band convergence studies because they have multiple bands near the valence bad edge that can be converged through various band engineering approaches providing power factor improvement opportunities. Theoretical calculations to identify the outcome of band convergence employ various approximations for the carrier scattering relaxation times (the most common being the constant relaxation time approximation) due to the high computational complexity involved in extracting them accurately. Here, we compare the outcome of strain-induced band convergence under two such scattering scenarios: i) the most commonly used constant relaxation time approximation and ii) energy dependent inter- and intra-valley scattering considerations for the half-Heuslers NbCoSn and TiCoSb. We show that the outcome of band convergence on the power factor depends on the carrier scattering assumptions, as well as the temperature. For both materials examined, band convergence improves the power factor. For NbCoSn, however, band convergence becomes more beneficial as temperature increases, under both scattering relaxation time assumptions. In the case of TiCoSb, on the other hand, constant relaxation time considerations also indicate that the relative power factor improvement increases with temperature, but under the energy dependent scattering time considerations, the relative improvement weakens with temperature. This indicates that the scattering details need to be accurately considered in band convergence studies to predict more accurate trends.",2011.04288v1 2021-10-05,Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor,"In superconductors, electrons with spin ${s=1/2}$ form Cooper pairs whose spin structure is usually singlet (${S=0}$) or triplet (${S=1}$). When the electronic structure near the Fermi level is characterized by fermions with angular momentum ${j=3/2}$ due to strong spin-orbit interactions, novel pairing states such as even-parity quintet (${J=2}$) and odd-parity septet (${J=3}$) states become allowed. Prime candidates for such exotic states are half-Heusler superconductors, which exhibit unconventional superconducting properties, but their pairing nature remains unsettled. Here we show that the superconductivity in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by the admixture of isotropic even-parity singlet and anisotropic odd-parity septet pairing, whose ratio can be tuned by electron irradiation. From magnetotransport and penetration depth measurements, we find that carrier concentrations and impurity scattering both increase with irradiation, resulting in a nonmonotonic change of the superconducting gap structure. Our findings shed new light on our fundamental understanding of unconventional superconducting states in topological materials.",2110.01819v2 2022-08-10,Defect engineering and Fermi-level tuning in half-Heusler topological semimetals,"Three-dimensional topological semimetals host a range of interesting quantum phenomena related to band crossing that give rise to Dirac or Weyl fermions, and can be potentially engineered into novel quantum devices. Harvesting the full potential of these materials will depend on our ability to position the Fermi level near the symmetry-protected band crossings so that their exotic spin and charge transport properties become prominent in the devices. Recent experiments on bulk and thin films of topological half-Heuslers show that the Fermi level is far from the symmetry-protected crossings, leading to strong interference from bulk bands in the observation of topologically protected surface states. Using density functional theory calculations we explore how intrinsic defects can be used to tune the Fermi level in the two representative half-Heusler topological semimetals PtLuSb and PtLuBi. Our results explain recent results of Hall and angle-resolved photoemission measurements. The calculations show that Pt vacancies are the most abundant intrinsic defects in these materials grown under typical growth conditions, and that these defects lead to excess hole densities that place the Fermi level significantly below the expected position in the pristine material. Directions for tuning the Fermi level by tuning chemical potentials are addressed.",2208.05415v2 2022-08-11,"Controlling the balance between remote, pinhole, and van der Waals epitaxy of Heusler films on graphene/sapphire","Remote epitaxy on monolayer graphene is promising for synthesis of highly lattice mismatched materials, exfoliation of free-standing membranes, and re-use of expensive substrates. However, clear experimental evidence of a remote mechanism remains elusive. In many cases, due to contaminants at the transferred graphene/substrate interface, alternative mechanisms such as pinhole-seeded lateral epitaxy or van der Waals epitaxy can explain the resulting exfoliatable single-crystalline films. Here, we find that growth of the Heusler compound GdPtSb on clean graphene on sapphire substrates produces a 30 degree rotated epitaxial superstructure that cannot be explained by pinhole or van der Waals epitaxy. With decreasing growth temperature the volume fraction of this 30 degree domain increases compared to the direct epitaxial 0 degree domain, which we attribute to slower surface diffusion at low temperature that favors remote epitaxy, compared to faster surface diffusion at high temperature that favors pinhole epitaxy. We further show that careful graphene/substrate annealing ($T\sim 700 ^\circ C$) and consideration of the film/substrate vs film/graphene lattice mismatch are required to obtain epitaxy to the underlying substrate for a variety of other Heusler films, including LaPtSb and GdAuGe. The 30 degree rotated superstructure provides a possible experimental fingerprint of remote epitaxy since it is inconsistent with the leading alternative mechanisms.",2208.05927v1 2022-10-14,Anti-site disorder and Berry curvature driven anomalous Hall effect in spin gapless semiconducting Mn2CoAl Heusler compound,"Spin gapless semiconductors exhibit a finite band gap for one spin channel and closed gap for other spin channel, emerged as a new state of magnetic materials with a great potential for spintronic applications. The first experimental evidence for the spin gapless semiconducting behavior was observed in an inverse Heusler compound Mn2CoAl. Here, we report a detailed investigation of the crystal structure and anomalous Hall effect in the Mn2CoAl using experimental and theoretical studies. The analysis of the high-resolution synchrotron x-ray diffraction data shows anti-site disorder between Mn and Al atoms within the inverse Heusler structure. The temperature-dependent resistivity shows semiconducting behavior and follows Mooijs criteria for disordered metal. Scaling behavior of the anomalous Hall resistivity suggests that the anomalous Hall effect in the Mn2CoAl is primarily governed by intrinsic mechanism due to the Berry curvature in momentum space. The experimental intrinsic anomalous Hall conductivity (AHC) is found to be 35 S/cm, which is considerably larger than the theoretically predicted value for ordered Mn2CoAl. Our first-principle calculations conclude that the anti-site disorder between Mn and Al atoms enhances the Berry curvature and hence the value of intrinsic AHC, which is in a very well agreement with the experiment.",2210.07668v1 2023-07-26,Giant spin-charge conversion in ultrathin films of the MnPtSb half-Heusler compound,"Half-metallic half-Heusler compounds with strong spin-orbit-coupling and broken inversion symmetry in their crystal structure are promising materials for generating and absorbing spin-currents, thus enabling the electric manipulation of magnetization in energy-efficient spintronic devices. In this work, we report the spin-to-charge conversion in sputtered ultrathin films of the half-Heusler compound MnPtSb with thickness (t) in the range from 1 to 6 nm. A combination of X-ray and transmission electron microscopy measurements evidence the epitaxial nature of these ultrathin non-centrosymmetric MnPtSb films, with a clear (111)-orientation obtained on top of (0001) single-crystal sapphire substrates. The study of the thickness (t)-dependent magnetization dynamics of the MnPtSb(t)/Co(5nm)/Au(5nm) heterostructure revealed that the MnPtSb compound can be used as an efficient spin current generator, even at film thicknesses as low as 1 nm. By making use of spin pumping FMR, we measure a remarkable t-dependent spin-charge conversion in the MnPtSb layers, which clearly demonstrate the interfacial origin of the conversion. When interpreted as arising from the inverse Edelstein effect (IEE), the spin-charge conversion efficiency extracted at room temperature for the thinnest MnPtSb layer reaches {\lambda}IEE~3 nm, representing an extremely high spin-charge conversion efficiency at room temperature. The still never explored ultrathin regime of the MnPtSb films studied in this work and the discover of their outstanding functionality are two ingredients which demonstrate the potentiality of such materials for future applications in spintronics.",2307.14516v1 2023-11-03,Giant tunneling magnetoresistance in Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi magnetic tunnel junction,"We propose a theoretical model for an all-Heusler magnetic tunnel junction that uses two Heusler compounds: Fe$_2$CrSi and Fe$_2$TiSi, both of which can be experimentally synthesized. Fe$_2$CrSi is a half-metallic ferromagnet, making it a promising material for efficient spin injection in magnetic random access memories and other spin-dependent devices. While, Fe$_2$TiSi is a nonmagnetic semiconductor that has the same lattice structure and comparable lattice constant with Fe$_2$CrSi, as it can be obtained by substituting the $Y$-site atoms in Fe$_2$CrSi. By using Fe$_2$TiSi as a tunneling barrier sandwiched by two pieces of semi-infinite Fe$_2$CrSi to construct an all-Heusler magnetic tunnel junction, the interface disorder is naturally reduced. Our calculations demonstrate that this magnetic tunnel junction can exhibit a giant tunneling magnetoresistance of up to 10$^{9}$\% and remains robust under finite bias voltage. These characteristics suggest that Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi MTJ will be an ideal candidate for future spintronic applications. More importantly, such a device model can keep such a giant tunneling magnetoresistance at and beyond room temperature due to the high Curie temperature of Fe$_2$CrSi.",2311.01772v1 2018-11-06,Probing alloy formation using different excitonic species: The particular case of InGaN,"Since the early 1960s, alloys are commonly grouped into two classes, featuring bound states in the bandgap (I) or additional, non-discrete band states (II). Microscopic material parameters for class I alloys can directly be extracted from photoluminescence (PL) spectra, whereas any conclusions drawn for class II alloys usually remain indirect and limited to macroscopic assertions. Nonetheless, here, we present a spectroscopic study on exciton localization in a so-called mixed crystal alloy (class II) that allows us to access microscopic alloy parameters. We study bulk In$_x$Ga$_{1-x}$N epilayers at the onset of alloy formation (0 $\leq$ $x$ $\leq$ 2.4%) in order to understand the material's particular robustness to defects. Based on an in-depth PL analysis it is demonstrated how different excitonic complexes (free, bound, and complex bound excitons) can serve as a probe to monitor the dilute limit of class II alloys. From an $x$-dependent linewidth analysis we extract the length scales at which excitons become increasingly localized, meaning that they convert from a free to a bound particle upon alloy formation. Already at x = 2.4% the average exciton diffusion length is reduced to 5.7 $\pm$ 1.3 nm at a temperature of 12 K, thus, detrimental exciton transfer mechanisms towards non-radiative defects are suppressed. In addition, the associated low temperature PL data suggests that a single indium atom does not suffice in order to permanently capture an exciton. Micro-PL spectra even give access to a forthright probing of silicon bound excitons embedded in a particular environment of indium atoms, thanks to the emergence of a hierarchy of individual, energetically sharp emission lines (full width at half maximum $\approx$ 300 $\mu$eV). Consequently, the present study allows us to extract first microscopic alloy properties formerly only accessible for class I alloys.",1811.02348v1 2019-07-30,Giant Enhancement of Solid Solubility in Monolayer BNC Alloys by Selective Orbital Coupling,"Solid solubility (SS) is one of the most important features of alloys, which is usually difficult to be largely tuned in the entire alloy concentrations by external approaches. Some alloys that were supposed to have promising physical properties could turn out to be much less useful because of their poor SS, e.g., the case for monolayer BNC [(BN)1-x(C2)x] alloys. Until now, an effective approach on significantly enhancing SS of (BN)1-x(C2)x in the entire x is still lacking. In this article, a novel mechanism of selective orbital coupling between high energy wrong-bond states and surface states mediated by the specific substrate has been proposed to stabilize the wrong-bonds and in turn significantly enhance the SS of (BN)1-x(C2)x alloys. Surprisingly, we demonstrate that five ordered alloys, exhibiting variable direct quasi-particle bandgaps from 1.35 to 3.99 eV, can spontaneously be formed at different x when (BN)1-x(C2)x is grown on hcp-phase Cr. Interestingly, the optical transitions around the band edges in these ordered alloys, accompanied by largely tunable exciton binding energies of ~1 eV at different x, are significantly strong due to their unique band structures. Importantly, the disordered (BN)1-x(C2)x alloys, exhibiting fully tunable bandgaps from 0 to ~6 eV in the entire x, can be formed on Cr substrate at the miscibility temperature of ~1200 K, which is greatly reduced compared to that of 4500~5600 K in free-standing form or on other substrates. Our discovery not only may resolve the long-standing SS problem of BNC alloys, but also could significantly extend the applications of BNC alloys for various optoelectronic applications.",1907.12847v1 2023-02-15,An experimental high-throughput to high-fidelity study towards discovering Al-Cr containing corrosion-resistant compositionally complex alloys,"Compositionally complex alloys hold the promise of simultaneously attaining superior combinations of properties, such as corrosion resistance, light-weighting, and strength. Achieving this goal is a challenge due in part to a large number of possible compositions and structures in the vast alloy design space. High-throughput methods offer a path forward, but a strong connection between the synthesis of an alloy of a given composition and structure with its properties has not been fully realized to date. Here, we present the rapid identification of corrosion-resistant alloys based on combinations of Al and Cr in a base Al-Co-Cr-Fe-Ni alloy. Previously unstudied alloy stoichiometries were identified using a combination of high-throughput experimental screening coupled with key metallurgical and electrochemical corrosion tests, identifying alloys with excellent passivation behavior. The alloy native oxide performance and its self-healing attributes were probed using rapid tests in deaerated 0.1 mol/L H2SO4. Importantly, a correlation was found between the electrochemical impedance modulus of the exposure-modified air-formed film and self-healing rate of the CCAs. Multi-element extended x-ray absorption fine structure analyses connected more ordered type chemical short-range order in the Ni-Al 1st nearest-neighbor shell to poorer corrosion resistance. This report underscores the utility of high throughput exploration of compositionally complex alloys for the identification and rapid screening of a vast stoichiometric space.",2302.07988v2 2023-06-14,Neural network as a tool for design of amorphous metal alloys with desired elastoplastic properties,"The development and implementation of the methods for designing amorphous metal alloys with desired mechanical properties is one of the most promising areas of modern materials science. Here, the machine learning methods appear to be a suitable complement to empirical methods related to the synthesis and testing of amorphous alloys of various compositions. In the present work, it is proposed a method to determine amorphous metal alloys with mechanical properties closest to those required. More than $50\,000$ amorphous alloys of different compositions have been considered, and the Young's modulus $E$ and the yield strength $\sigma_{y}$ have been evaluated for them by the machine learning model trained on the fundamental physical properties of the chemical elements. Statistical treatment of the obtained results reveals that the fundamental physical properties of the chemical element with the largest mass fraction are the most significant factors, whose values correlate with the values of the mechanical properties of the alloys, in which this element is involved. It is shown that the values of the Young's modulus $E$ and the yield strength $\sigma_{y}$ are higher for amorphous alloys based on Cr, Fe, Co, Ni, Nb, Mo and W formed by the addition of semimetals (e.g. Be, B, Al, Sn), nonmetals (e.g. Si and P) and lanthanides (e.g. La and Gd) than for alloys of other compositions. Increasing the number of components in alloy from $2$ to $7$ and changing the mass fraction of chemical elements has no significantly impact on the strength characteristics $E$ and $\sigma_{y}$. Amorphous metal alloys with the most improved mechanical properties have been identified. In particular, such extremely high-strength alloys include Cr$_{80}$B$_{20}$ (among binary), Mo$_{60}$B$_{20}$W$_{20}$ (among ternary) and Cr$_{40}$B$_{20}$Nb$_{10}$Pd$_{10}$Ta$_{10}$Si$_{10}$ (among multicomponent).",2306.08383v1 2024-03-20,Effect of annealing on the hot salt corrosion resistance of the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr obtained via cold Rotary Swaging,"A hot salt corrosion (HSC) test was performed on the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr (Russian industrial alloy PT-7M). The ultrafine-grained (UFG) microstructure in the titanium alpha-alloy was formed via cold Rotary Swaging. The grain size and volume fraction of the recrystallized microstructure in the alloy were varied by choosing appropriate annealing temperatures and times. The microstructure and corrosion resistance of UFG alloys were studied after 30 min of annealing at 500-700C and after 1000 h of annealing at 250C. Metallographic studies were carried out to investigate the effects of annealing on the nature and extent of corrosive damage in the titanium alpha-alloy Ti-2.5Al-2.6Zr. After HSC tests, surface analyses of the titanium alpha-alloy samples were conducted using X-ray diffraction and electron microscopy. During the HSC testing of the titanium alpha-alloy Ti-2.5Al-2.6Zr, a competitive interaction between intergranular corrosion (IGC) and pitting corrosion was observed. To the best of our knowledge, it was shown for the first time that annealing affects the relationship among the IGC, pitting corrosion and uniform corrosion rates of the titanium alloy. Prolonged low-temperature annealing at 250C resulted in a more pronounced increase in the uniform corrosion rate than short-term high-temperature annealing for 30 min at 500-700C. An in-depth analysis of the effect of the structure and phase composition of the grain boundaries on the susceptibility of the alpha-alloy Ti-2.5Al-2.6Zr to HSC was conducted.",2403.13587v1 2007-10-11,The value of long-range interactions parameter for some alloys,"The critical behavior of some alloys are analyzed within the framework of Heisenbergs model with long-range interaction. On based experimental values of the critical exponent $\gamma$ we calculate the value of paerameter of long-range interaction.",0710.2196v1 2008-11-03,Ab initio calculation of structural and electronic properties of Al$_x$Ga$_{1-x}$N and In$_x$Ga$_{1-x}$N alloys,"Using the density functional theory (DFT) with the generalized gradient approximation (GGA), the structural and electronic properties of wurtzite AlN, GaN, InN, and their related alloys, Al$_x$Ga$_{1-x}$N and In$_x$Ga$_{1-x}$N, were calculated. We have performed accurate {\it ab initio} total energy calculations using the full--potential linearized augmented plane wave (FP--LAPW) method to investigate the structural and electronic properties. In both alloys we found that the fundamental parameters do not follow Vegard's law. The lattice parameters, $a, c,$ and $u$, for the Al$_x$Ga$_{1-x}$N alloy are found to exhibit downward bowing, while for In$_x$Ga$_{1-x}$N there is an upward bowing for the $a$ and $c$ parameters and a downward bowing for the internal parameter, $u$. Furthermore, we found that for both alloys, the band gap value does not follow Vegard's law. As a by--product of our electronic band structure calculations, the effective masses of the binary compounds as well as their related alloys were calculated. We show that the calculated properties for the binary compounds, as well as for the studied alloys, show good agreement with most of the previously reported results. Finally, using the frozen phonon approach, the A$_1(TO)$ mode for the different systems studied in this work was calculated. Our calculations show good agreement with experimental values reported for the binary compounds. For the ternary alloys, our calculations reproduce experimental values for Al$_x$Ga$_{1-x}$N as well as theoretical predictions for In$_x$Ga$_{1-x}$N.",0811.0380v1 2009-08-30,Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys,"Weakly ferromagnetic alloys are being used by several groups in the study of superconducting/ferromagnetic hybrid systems. Because spin-flip and spin-orbit scattering in such alloys disrupt the penetration of pair correlations into the ferromagnetic material, it is desirable to have a direct measurement of the spin memory length in such alloys. We have measured the spin memory length at 4.2 K in sputtered Pd0.88Ni0.12 and Pd0.987Fe0.013 alloys using methods based on current-perpendicular-to-plane giant magnetoresistance. The alloys are incorporated into hybrid spin valves of various types, and the spin memory length is determined by fits of the Valet-Fert spin-transport equations to data of magnetoresistance vs. alloy thickness. For the case of PdNi alloy, the resulting values of the spin memory length are lsf(PdNi) = 2.8 +/- 0.5 nm and 5.4 +/- 0.6 nm, depending on whether or not the PdNi is exchange biased by an adjacent Permalloy layer. For PdFe, the spin memory length is somewhat longer, lsf(PdFe) = 9.6 +/- 2 nm, consistent with earlier measurements indicating lower spin-orbit scattering in that material. Unfortunately, even the longer spin memory length in PdFe may not be long enough to facilitate observation of spin-triplet superconducting correlations predicted to occur in superconducting/ferromagnetic hybrid systems in the presence of magnetic inhomogeneity.",0908.4375v1 2010-04-14,Spectral properties of discrete alloy-type models,"We discuss recent results on spectral properties of discrete alloy-type random Schr\""odinger operators. They concern Wegner estimates and bounds on the fractional moments of the Green's function.",1004.2385v1 2010-08-31,Internal friction study of dislocation dynamics in thermally aged Fe-1%Cu-C alloys,"Internal friction study of dislocation dynamics in thermally aged Fe-1%Cu-C alloys.",1008.5262v3 2012-01-05,The influence of transition metal solutes on dislocation core structure and values of Peierls stress and barrier in tungsten,"Several transition metals were examined to evaluate their potential for improving the ductility of tungsten. The dislocation core structure and Peierls stress and barrier of $1/2<111>$ screw dislocations in binary tungsten-transition metal alloys (W$_{1-x}$TM$_{x}$) were investigated using first principles electronic structure calculations. The periodic quadrupole approach was applied to model the structure of $1/2<111>$ dislocation. Alloying with transition metals was modeled using the virtual crystal approximation and the applicability of this approach was assessed by calculating the equilibrium lattice parameter and elastic constants of the tungsten alloys. Reasonable agreement was obtained with experimental data and with results obtained from the conventional supercell approach. Increasing the concentration of a transition metal from the VIIIA group, i.e. the elements in columns headed by Fe, Co and Ni, leads to reduction of the $C^\prime$ elastic constant and increase of elastic anisotropy A=$C_{44}/C^\prime$. Alloying W with a group VIIIA transition metal changes the structure of the dislocation core from symmetric to asymmetric, similar to results obtained for W$_{1-x}$Re$_{x}$ alloys in the earlier work of Romaner {\it et al} (Phys. Rev. Lett. 104, 195503 (2010))\comments{\cite{WRECORE}}. In addition to a change in the core symmetry, the values of the Peierls stress and barrier are reduced. The latter effect could lead to increased ductility in a tungsten-based alloy\comments{\cite{WRECORE}}. Our results demonstrate that alloying with any of the transition metals from the VIIIA group should have similar effect as alloying with Re.",1201.1245v2 2012-02-15,Monte Carlo simulations of the structure of Pt-based bimetallic nanoparticles,"Pt-based bimetallic nanoparticles have attracted significant attention as a promising replacement for expensive Pt nanoparticles. In the systematic design of bimetallic nanoparticles, it is important to understand their preferred atomic structures. However, compared with unary systems, alloy nanoparticles present more structural complexity with various compositional configurations, such as mixed-alloy, core-shell, and multishell structures. In this paper, we developed a unified empirical potential model for various Pt-based binary alloys, such as Pd-Pt, Cu-Pt, Au-Pt, and Ag-Pt. Within this framework, we performed a series of Monte Carlo (MC) simulations that quantify the energetically favorable atomic arrangements of Pt-based alloy nanoparticles: an intermetallic compound structure for the Pd-Pt alloy, an onion-like multi-shell structure for the Cu-Pt alloy, and core-shell structures (Au@Pt and Ag@Pt) for the Au-Pt and Ag-Pt alloys. The equilibrium nanoparticle structures for the four alloy types were compared with each other, and the structural features can be interpreted by the interplay of their material properties, such as the surface energy and heat of formation.",1202.3277v2 2013-09-06,Interplay of force constants in the lattice dynamics of disordered alloys : An ab-initio study,"A reliable prediction of interatomic force constants in disordered alloys is an outstanding problem. This is due to the need for a proper treatment of multisite (atleast pair) correlation within a random environment. The situation becomes even more challenging for systems with large difference in atomic size and mass. We propose a systematic density functional theory (DFT) based study to predict the ab-initio force constants in random alloys. The method is based on a marriage between special quasirandom structures (SQS) and the augmented space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc. bcc TaW and fcc NiPt alloys are considered as the two distinct test cases. Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than those in pure Ta (W), which, in turn, yields stiffer (softer) force constants for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be softer compared to Ni-Ni, due to a large bond distance of the former. Our calculated force constants, phonon spectra and DOS are compared with experiments and other theoretical results, wherever available. Correct trend of present results for the two alloys pave a path for further future studies in more complex alloy systems.",1309.1589v2 2016-09-21,"Magnetic Susceptibility of Dirac Fermions, Bi-Sb Alloys, Interacting Bloch Fermions, Dilute Nonmagnetic Alloys, and Kondo Alloys","Wide ranging interest in Dirac Hamiltomian is due to the emergence of novel materials, namely, graphene, topological insulators and superconductors, the newly-discovered Weyl semimetals, and still actively-sought after Majorana fermions in real materials. We give a brief review of the relativistic Dirac quantum mechanics and its impact in the developments of modern physics. The quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory with the experiments on Bi-Sb alloys has been achieved, and physically meaningful contributions to the diamagnetism has been identified. We also treat relativistic Dirac fermion as an interband dynamics in uniform magnetic fields. For the interacting Bloch electrons, the role of translation symmetry for calculating the magnetic susceptibility avoids any approximation to second order in the field. The magnetic susceptibility of Hubbard model and those of Fermi liquids are readily obtained as limiting cases. The expressions for magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical foundation of the empirical formulas used in fitting experimental results. For completeness, the magnetic susceptibility of dilute magnetic or Kondo alloys is also given for high and low temperature regimes.",1609.06419v1 2018-01-01,Structural Disorder and Electronic Structure in Alloyed SrTiO3/SrFeO2.5 Compounds: A Theoretical Study,"Many mixed ionic/electronic conductors (MIECs) applied in fuel cell electrodes can be considered as alloys between perovskite oxides and ordered oxygen vacancy compounds. For example, in the model MIEC (STF), low oxygen diffusion barrier exist in SrTiO3 lattice, when it has been mixed with SrFeO2.5 with intrinsic oxygen deficiency, the ionic conductivity can be greatly improved. Meanwhile, the electronic conductivity can be optimized by controlling the defect chemistry of the alloy. However, the configurational space is too large in such alloys so that it is difficult for direct atomic modeling, which hinders in-depth understanding and predictive modeling. In this work, we present a cluster expansion model to describe the energetics of the disordered SrTiO3/SrFeO2.5 alloy within the full solid solution composition space Sr(Ti1-x,Fex)O3-0.5x (0L1_0 transformations after a quench of an alloy from the disordered A1 phase to the single-phase L1_0 state for a number of alloy models with different chemical interactions, temperatures, concentrations, and tetragonal distortions. We find a number of peculiar features in both transient microstructures and transformation kinetics, many of them agreeng well with experimental data. The simulations also demonstrate a phenomenon of an interaction-dependent alignment of antiphase boundaries in nearly-equilibrium twinned bands which seems to be observed in some experiments.",0108422v1 2002-02-21,Screened Coulomb interactions in metallic alloys: I. Universal screening in the atomic sphere approximation,"We have used the locally self-consistent Green's function (LSGF) method in supercell calculations to establish the distribution of the net charges assigned to the atomic spheres of the alloy components in metallic alloys with different compositions and degrees of order. This allows us to determine the Madelung potential energy of a random alloy in the single-site mean field approximation which makes the conventional single-site density-functional- theory coherent potential approximation (SS-DFT-CPA) method practically identical to the supercell LSGF method with a single-site local interaction zone that yields an exact solution of the DFT problem. We demonstrate that the basic mechanism which governs the charge distribution is the screening of the net charges of the alloy components that makes the direct Coulomb interactions short-ranged. In the atomic sphere approximation, this screening appears to be almost independent of the alloy composition, lattice spacing, and crystal structure. A formalism which allows a consistent treatment of the screened Coulomb interactions within the single-site mean-filed approximation is outlined. We also derive the contribution of the screened Coulomb interactions to the S2 formalism and the generalized perturbation method.",0202370v1 2003-04-29,"EXAFS, XRD and RMC studies of an Amorphous Ga$_{50}$Se$_{50}$ Alloy Produced by Mechanical Alloying","The local atomic order of an amorphous Ga$_{50}$Se$_{50}$ alloy produced by Mechanical Alloying (MA) was studied by the Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Diffraction (XRD) techniques and by Reverse Monte Carlo (RMC) simulations of its total x-ray structure factor. The coordination numbers and interatomic distances for the first neighbors were determined by means of EXAFS analysis and RMC simulations. The RMC simulations also furnished the partial pair distribution functions $G^{\text{RMC}}_{\text{Ga-Ga}}(r)$, $G^{\text{RMC}}_{\text{Ga-Se}}(r)$ and $G^{\text{RMC}}_{\text{Se-Se}}(r)$. The results obtained indicated that there are important differences among the local structure of the amorphous Ga$_{50}$Se$_{50}$ alloy produced by MA and those of the corresponding crystals, since there are Se-Se pairs in the first coordination shell of the amorphous alloy that are forbidden in the Ga$_{50}$Se$_{50}$ crystals.",0304666v1 2004-01-31,Reverse Monte Carlo Simulations and Raman Scattering of an Amorphous GeSe$_4$ Alloy Produced by Mechanical Alloying,"The short and intermediate range order of an amorphous GeSe$_4$ alloy produced by Mechanical Alloying were studied by Reverse Monte Carlo simulations of its x-ray total structure factor and Raman scattering. The simulations were used to compute the $G^{\text{RMC}}_{\text{Ge-Ge}}(r)$, $G^{\text{RMC}}_{\text{Ge-Se}}(r)$ and $G^{\text{RMC}}_{\text{Se-Se}}(r)$ partial distribution functions and the ${\cal S}^{\text{RMC}}_{\text{Ge-Ge}}(K)$, ${\cal S}^{\text{RMC}}_{\text{Ge-Se}}(K)$ and ${\cal S}^{\text{RMC}}_{\text{Se-Se}}(K)$ partial structure factors. We calculated the coordination numbers and interatomic distances for the first and second neighbors and the bond-angle distribution functions $\Theta_{ijl}(\cos\theta)$. The data obtained indicate that the structure of the alloy has important differences when compared to alloys prepared by other techniques. There are a high number of Se-Se pairs in the first shell, and some of the tetrahedral units formed seemed to be connected by Se-Se bridges.",0402015v1 2006-04-04,Comparative study of the Portevin-Le Chatelier effect in interstitial and substitutional alloy,"Tensile tests were carried out by deforming polycrystalline samples of an interstitial alloy, low carbon steel at room temperature in a wide range of strain rates where the Portevin-Le Chatelier (PLC) effect was observed. The observed stress time series data were analyzed using the nonlinear dynamical methods. From the analyses, we could establish the presence of marginal deterministic chaos in the PLC effect of the low carbon steel. Moreover, we made a comparative study of the PLC effect of this interstitial alloy with the substitutional Al-Mg alloy which shows that the dynamics of the PLC effect in the interstitial alloy is more complex compared to that of the substitutional alloy.",0604080v2 2006-05-30,Complex Precipitation Pathways in Multi-Component Alloys,"One usual way to strengthen a metal is to add alloying elements and to control the size and the density of the precipitates obtained. However, precipitation in multicomponent alloys can take complex pathways depending on the relative diffusivity of solute atoms and on the relative driving forces involved. In Al-Zr-Sc alloys, atomic simulations based on first-principle calculations combined with various complementary experimental approaches working at different scales reveal a strongly inhomogeneous structure of the precipitates: owing to the much faster diffusivity of Sc compared with Zr in the solid solution, and to the absence of Zr and Sc diffusion inside the precipitates, the precipitate core is mostly Sc-rich, whereas the external shell is Zr-rich. This explains previous observations of an enhanced nucleation rate in Al-Zr-Sc alloys compared with binary Al-Sc alloys, along with much higher resistance to Ostwald ripening, two features of the utmost importance in the field of light high-strength materials.",0605738v1 2008-11-22,A simple theory of the Invar effect in iron-nickel alloys,"Certain alloys of iron and nickel (so-called 'Invar' alloys) exhibit almost no thermal expansion over a wide range of temperature. It is clear that this is the result of an anomalous contraction upon heating which counteracts the normal thermal expansion arising from the anharmonicity of lattice vibrations. This anomalous contraction seems to be related to the alloys' magnetic properties, since the effect vanishes at a temperature close to the Curie temperature. However, despite many years of intensive research, a widely accepted microscopic theory of the Invar effect in face-centered-cubic Fe-Ni alloys is still lacking. Here we present a simple theory of the Invar effect in these alloys based on Ising magnetism, ab initio total energy calculations, and the Debye-Gruneisen model. We show that this theory accurately reproduces several well known properties of these materials, including Guillaume's famous plot1 of the thermal expansion coefficient as a function of the concentration of nickel. Within the same framework, we are able to account in a straightforward way for experimentally observed deviations from Vegard's law. Our approach supports the idea that the lattice constant is governed by a few parameters, including the fraction of iron-iron nearest-neighbour pairs.",0811.3673v1 2010-11-08,Tuning the spin texture in binary and ternary surface alloys on Ag(111),"Recently, a giant spin splitting has been observed in surface alloys on noble metal (111) surfaces as a result of a strong structural modification at the surface as well as the large atomic spin-orbit interaction (SOI) of the alloy atoms. These surface alloys are an ideal playground to manipulate both the size of the spin splitting as well as the position of the Fermi level as it is possible to change the atomic SOI as well as the relaxation by varying alloy atoms and substrates. Using spin- and angle-resolved photoemission spectroscopy in combination with quantitative low energy electron diffraction we have studied the mixed binary Bi(x)Sb(1-x)/Ag(111) and the mixed ternary Bi(x)Pb(y)Sb(1-x-y)/Ag(111) surface alloys where we observed a continuous evolution of the band structure with x and y.",1011.1829v1 2011-09-14,"The Effect of dopants on magnetic properties of the ordered Fe_{65-x}Al_{35-y}M_{x,y} (M=Ga,B,V; x,y=5,10) alloys","The results of X-ray diffraction, complex in-field (up to 9 T) and temperature (5-300 K) Moessbauer and magnetometric studies of the ordered Fe_{65}Al_{35-x}M_x (M=Ga, B; x=0,5,10) and Fe_{65-x}V_xAl_{35} (x=5,10) alloys are presented. Analysis of the magnetometry studies shows that the systems Fe_{65}Al_{35} and Fe_{65}Al_{35-x}Ga_x (x=5, 10) are characterized by two different magnetic states with essentially distinguishing hysteresis loops and AC susceptibility values. The temperature and external magnetic field values inducing the transition from one magnetic state to another are higher in the Ga-doped alloys than in the reference Fe_{65}Al_{35} alloy. The boron addition transforms the magnetic state of the initial alloy Fe_{65}Al_{35} into a ferromagnetic one exhibiting high magnetic characteristics. Substitution of V for Fe in the ternary alloys Fe_{65-x}V_xAl_{35} results in reduction of magnetic characteristics and collapsing of 57Fe hyperfine magnetic filed.",1109.3064v1 2011-11-21,Ab initio theory of galvanomagnetic phenomena in ferromagnetic metals and disordered alloys,"We present an ab initio theory of transport quantities of metallic ferromagnets developed in the framework of the fully relativistic tight-binding linear muffin-tin orbital method. The approach is based on the Kubo-Streda formula for the conductivity tensor, on the coherent potential approximation for random alloys, and on the concept of interatomic electron transport. The developed formalism is applied to pure 3d transition metals (Fe, Co, Ni) and to random Ni-based ferromagnetic alloys (Ni-Fe, Ni-Co, Ni-Mn). High values of the anisotropic magnetoresistance (AMR), found for Ni-rich alloys, are explained by a negligible disorder in the majority spin channel while a change of the sign of the anomalous Hall effect (AHE) on alloying is interpreted as a band-filling effect without a direct relation to the high AMR. The influence of disorder on the AHE in concentrated alloys is investigated as well.",1111.4793v2 2012-04-20,First-principles based modeling of hydrogen permeation through Pd-Cu alloys,"The solubility and diffusivity of hydrogen in disordered Pd1-xCux alloys are investigated using a combination of first-principles calculations, a composition-dependent local cluster expansion (CDLCE) technique, and kinetic Monte Carlo simulations. We demonstrate that a linear CDCLE model can already accurately describe interstitial H in Pd1-xCux alloys over the entire composition range (0\leqx\leq1) with accuracy comparable to that of direct first-principles calculations. Our predicted H solubility and permeability results are in reasonable agreement with experimental measurements. The proposed model is quite general and can be employed to rapidly and accurately screen a large number of alloy compositions for potential membrane applications. Extension to ternary or higher-order alloy systems should be straightforward. Our study also highlights the significant effect of local lattice relaxations on H energetics in size-mismatched disordered alloys, which has been largely overlooked in the literature.",1204.4512v1 2012-10-03,Magnetic anisotropy energy of disordered tetragonal Fe-Co systems from ab initio alloy theory,"We present results of systematic fully relativistic first-principles calculations of the uniaxial magnetic anisotropy energy (MAE) of a disordered and partially ordered tetragonal Fe-Co alloy using the coherent potential approximation (CPA). This alloy has recently become a promising system for thin ferromagnetic films with a perpendicular magnetic anisotropy. We find that existing theoretical approaches to homogeneous random bulk Fe-Co alloys, based on a simple virtual crystal approximation (VCA), overestimate the maximum MAE values obtained in the CPA by a factor of four. This pronounced difference is ascribed to the strong disorder in the minority spin channel of real alloys, which is neglected in the VCA and which leads to a broadening of the d-like eigenstates at the Fermi energy and to the reduction of the MAE. The ordered Fe-Co alloys with a maximum L1_0-like atomic long-range order can exhibit high values of the MAE, which, however, get dramatically reduced by small perturbations of the perfect order.",1210.1028v2 2013-01-10,First-principles calculation of the Gilbert damping parameter via the linear response formalism with application to magnetic transition-metals and alloys,"A method for the calculations of the Gilbert damping parameter $\alpha$ is presented, which based on the linear response formalism, has been implemented within the fully relativistic Korringa-Kohn-Rostoker band structure method in combination with the coherent potential approximation alloy theory. To account for thermal displacements of atoms as a scattering mechanism, an alloy-analogy model is introduced. This allows the determination of $\alpha$ for various types of materials, such as elemental magnetic systems and ordered magnetic compounds at finite temperature, as well as for disordered magnetic alloys at $T = 0$ K and above. The effects of spin-orbit coupling, chemical and temperature induced structural disorder are analyzed. Calculations have been performed for the 3$d$ transition-metals bcc Fe, hcp Co, and fcc Ni, their binary alloys bcc Fe$_{1-x}$Co$_{x}$, fcc Ni$_{1-x}$Fe$_x$, fcc Ni$_{1-x}$Co$_x$ and bcc Fe$_{1-x}$V$_{x}$, and for 5d impurities in transition-metal alloys. All results are in satisfying agreement with experiment.",1301.2114v1 2013-11-15,Effects of Irradiation Temperature and Dose Rate on the Mechanical Properties of Self-Ion Implanted Fe and Fe-Cr Alloys,"Pure Fe and model Fe-Cr alloys containing 5, 10 and 14%Cr were irradiated with Fe+ ions at a maximum energy of 2MeV to the same dose of 0.6dpa at temperatures of 300 C, 400 C and 500 C, and at dose rates corresponding to 6 x 10-4 dpa/s and 3 x 10-5 dpa/s. All materials exhibited an increase in hardness after irradiation at 300 C. After irradiation at 400 C, hardening was observed only in Fe-Cr alloys, and not in the pure Fe. After irradiation at 500 C, no hardening was observed in any of the materials tested. For irradiations at both 300 C and 400 C, greater hardening was found in the Fe-Cr alloys irradiated at the lower dose rate. Transmission electron microscopy and atom probe tomography of Fe 5%Cr identified larger dislocation loop densities and sizes in the alloy irradiated with the high dose rate and Cr precipitation in the alloy irradiated with the low dose rate.",1311.3786v1 2014-05-09,"Thermodynamics, kinetics and fragility of bulk metallic glass forming liquids","This review deals with the kinetic and thermodynamic fragility of bulk metallic glass forming liquids. The experimental methods to determine the kinetic fragility, relaxation behavior and thermodynamic functions of undercooled metallic liquids are introduced. Existing data are assessed and discussed using the Vogel-Fulcher-Tammann equation and in the frameworks of the Adam-Gibbs as well as the Cohen-Turnbull free volume approach. In contrast to pure metals and most non glass forming alloys, bulk glass formers are moderately strong liquids. In general the fragility parameter $D^{*} $ increases with the complexity of the alloy with differences between the alloy families, e.g. noble-metal based alloys being more fragile than Zr-based alloys. At least some bulk metallic glass forming liquids, such as Vitreloy 1, undergo transitions from a fragile state at high temperatures to a strong state at low temperatures with indications that in Zr-based alloys this behavior is a common phenomenon.",1405.2251v1 2014-11-01,Ferromagnetic interactions and martensitic transformation in Fe doped Ni-Mn-In shape memory alloys,"The structure, magnetic and martensitic properties of Fe doped Ni-Mn-In magnetic shape memory alloys have been studied by differential scanning calorimetry, magnetization, resistivity, X-ray diffraction (XRD) and EXAFS. While Ni$_{2}$MnIn$_{1-x}$Fe$_{x}$ ($0 \le x \le 0.6$) alloys are ferromagnetic and non martensitic, the martensitic transformation temperature in Ni$_{2}$Mn$_{1.5} $In$_{1-y}$Fe$_{y}$ and Ni$_{2}$Mn$ _{1.6} $In$_{1-y}$Fe$_{y}$ increases for lower Fe concentrations ($y \le 0.05$) before decreasing sharply for higher Fe concentrations. XRD analysis reveals presence of cubic and tetragonal structural phases in Ni$_{2}$MnIn$_{1-x}$Fe$_{x}$ at room temperature with tetragonal phase content increasing with Fe doping. Even though the local structure around Mn and Ni in these Fe doped alloys is similar to martensitic Mn rich Ni-Mn-In alloys, presence of ferromagnetic interactions and structural disorder induced by Fe affect Mn-Ni-Mn antiferromagnetic interactions resulting in suppression of martensitic transformation in these Fe doped alloys.",1411.0058v1 2015-05-04,Analyzing Alloy Formulas using an SMT Solver: A Case Study,"This paper describes how Yices, a modern SAT Modulo theories solver, can be used to analyze the address-book problem expressed in Alloy, a first-order relational logic with transitive closure. Current analysis of Alloy models - as performed by the Alloy Analyzer - is based on SAT solving and thus, is done only with respect to finitized types. Our analysis generalizes this approach by taking advantage of the background theories available in Yices, and avoiding type finitization when possible. Consequently, it is potentially capable of proving that an assertion is a tautology - a capability completely missing from the Alloy Analyzer. This paper also reports on our experimental results that compare the performance of our analysis to that of the Alloy Analyzer for various versions of the address book problem.",1505.00672v1 2015-06-12,"Ab initio study of structural, electronic, and thermal properties of Ir$_{1-x}$Rh$_{x}$ alloys","The structural, electronic, mechanical and thermal properties of Ir$_{1-x}$Rh$_{x}$ alloys were studied systematically using ab initio density functional theory at different concentrations (x = 0.00, 0.25, 0.50, 0.75, 1.00). A Special Quasirandom Structure method was used to make alloys having FCC structure with four atoms per unit cell. The ground state properties such as lattice constant and bulk modulus were calculated to find the equilibrium atomic position for stable alloys. The calculated ground state properties are in good agreement with the experimental and previously presented other theoretical data. The electronic band structure and density of states were calculated to study the electronic properties for these alloys at different concentrations. The electronic properties substantiate the metallic behavior of alloys. The first principle density functional perturbation theory as implemented in quasiharmonic approximation was used for the calculation of thermal properties. We have calculated the thermal properties such as Debye temperatures, vibration energy, entropy, constant-volume specific heat and internal energy. The ab initio linear-response method was used to calculate phonon densities of states.",1506.03966v1 2015-07-23,Deformation behavior of Mg-8.5wt.%Al alloy under reverse loading investigated by in-situ neutron diffraction and elastic viscoplastic self-consistent modeling,"The cyclic deformation behavior of extruded Mg-8.5wt.%Al alloy with a conventional extrusion texture and a modified texture is systematically investigated by in-situ neutron diffraction and elastic viscoplastic self-consistent (EVPSC) modeling incorporating a twinning/de-twinning (TDT) scheme. The role of twinning and de-twinning on the deformation behavior of Mg-8.5wt.% Al alloy is investigated in terms of the macroscopic stress-strain response, the evolution of the activities of various deformation mechanisms, the texture evolution, the evolution of the internal elastic strains, and the evolution of the diffraction peak intensities. The alloy with the conventional extrusion texture undergoes twinning during initial compression and de-twinning during reverse tension. The same alloy does not favor twinning during initial tension, but rather during reverse compression. The alloy with a modified texture undergoes twinning during initial tension followed by detwinning during reverse compression. The results provide insights into the effect of initial texture, loading path, slip, twinning, de-twinning on the cyclic behavior of magnesium.",1507.06384v1 2016-01-11,Water-Induced Bimetallic Alloy Surface Segregation: A First Principle Study,"Bimetallic alloys have drawn extensive attentions in materials science due to their widespread applications in electronics, engineering and catalysis. A very fundamental question of alloy is its surface segregation phenomenon. Many recent observations have shown that reactive gases or supports may have strong effects on alloy segregation. However, segregation in water, the most common solvent and environment, has not received enough attention. In this paper we give the quantitative descriptions on the surface segregation energies of 23 transition-metal impurities in Cu hosts under the conditions of water adsorption by performing density functional theory (DFT) calculations. The general trends in the changes of segregation energies caused by water adsorption are established. Our results show water adsorption could induce strong surface segregation tendencies for early and middle transition metals in Cu alloys. This finding not only prompts us to re-examine the potential effects of water on bimetallic alloy surfaces, but would be also very helpful as a guide for the further theoretical and experimental studies in this field.",1601.02346v1 2016-01-27,"On the origin of bulk glass forming ability in Cu-Hf, Zr alloys","Understanding the formation of bulk metallic glasses (BMG) in metallic systems and finding a reliable criterion for selection of BMG compositions are among the most important issues in condensed matter physics and material science. Using the results of magnetic susceptibility measurements performed on both amorphous and crystallized Cu-Hf alloys (30-70 at% Cu) we find a correlation between the difference in magnetic susceptibilities of corresponding glassy and crystalline alloys and the variation in the glass forming ability (GFA) in these alloys. Since the same correlation can be inferred from data for the properties associated with the electronic structure of Cu-Zr alloys, it seems quite general and may apply to other glassy alloys based on early and late transition metals. This correlation is plausible from the free energy considerations and provides a simple way to select the compositions with high GFA.",1601.07397v2 2016-10-12,Effect of Electron Count and Chemical Complexity in the Ta-Nb-Hf-Zr-Ti High-Entropy Alloy Superconductor,"High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered BCC Ta-Nb-Hf-Zr-Ti high entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials, e.g. it has a well defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence-electron count dependence of the superconducting transition temperature in the high entropy alloy falls between those of analogous simple solid solutions and amorphous materials, and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellent intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials.",1610.03746v1 2016-11-03,High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi,"High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring over a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.",1611.00876v2 2017-01-09,"Magnetic properties of ultra-thin 3d transition-metal binary alloys I: spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior","The structure and static magnetic properties - saturation magnetization, perpendicular anisotropy, spectroscopic g-factor, and orbital magnetization - of thin-film 3d transition metal alloys are determined over the full range of alloy compositions via X-ray diffraction, magnetometry, and ferromagnetic resonance measurements. We determine the interfacial perpendicular magnetic anisotropy by use of samples sets with varying thickness for specific alloy concentrations. The results agree with prior published data and theoretical predictions. They provide a comprehensive compilation of the magnetic properties of thin-film Ni-Co, Ni-Fe and Co-Fe alloys that goes well beyond the often-cited Slater-Pauling dependence of magnetic moment on alloy concentration.",1701.02177v1 2017-07-29,Experimental study of extrinsic spin Hall effect in CuPt alloy,"We have experimentally studied the effects on the spin Hall angle due to systematic addition of Pt into the light metal Cu. We perform spin torque ferromagnetic resonance measurements on Py/CuPt bilayer and find that as the Pt concentration increases, the spin Hall angle of CuPt alloy increases. Moreover, only 28% Pt in CuPt alloy can give rise to a spin Hall angle close to that of Pt. We further extract the spin Hall resistivity of CuPt alloy for different Pt concentrations and find that the contribution of skew scattering is larger for lower Pt concentrations, while the side-jump contribution is larger for higher Pt concentrations. From technological perspective, since the CuPt alloy can sustain high processing temperatures and Cu is the most common metallization element in the Si platform, it would be easier to integrate the CuPt alloy based spintronic devices into existing Si fabrication technology.",1707.09525v1 2018-03-27,Evidence of multiband superconductivity in the $β$-phase Mo$_{1-x}$Re$_x$ alloys,"We present a detailed study of the superconducting properties in the beta-phase Mo$_{1-x}$Re$_x$ (x = 0.25 and 0.4) solid solution alloys pursued through magnetization and heat capacity measurements. The temperature dependence of the upper critical field H$_{C2}$(T) in these binary alloys shows a deviation from the prediction of the Werthamer-Helfand-Hohenberg (WHH) theory. The temperature dependence of superfluid density estimated from the variation of lower critical field H$_{C1}$ with temperature, cannot be explained within the framework of a single superconducting energy gap. The heat capacity also shows an anomalous feature in its temperature dependence. All these results can be reasonably explained by considering the existence of two superconducting energy gaps in these Mo$_{1-x}$Re$_x$ alloys. Initial results of electronic structure calculations and resonant photoelectron spectroscopy measurements support this possibility and suggest that the Re-5d like states at the Fermi level may not intermix with the Mo-5p and 5s like states in the beta-phase Mo$_{1-x}$Re$_x$ alloys and contribute quite distinctly to the superconductivity of these alloys.",1803.10315v1 2018-11-03,Modern Data Analytics Approach to Predict Creep of High-Temperature Alloys,"A breakthrough in alloy design often requires comprehensive understanding in complex multi-component/multi-phase systems to generate novel material hypotheses. We introduce a modern data analytics workflow that leverages high-quality experimental data augmented with advanced features obtained from high-fidelity models. Herein, we use an example of a consistently-measured creep dataset of developmental high-temperature alloy combined with scientific alloy features populated from a high-throughput computational thermodynamic approach. Extensive correlation analyses provide ranking insights for most impactful alloy features for creep resistance, evaluated from a large set of candidate features suggested by domain experts. We also show that we can accurately train machine learning models by integrating high-ranking features obtained from correlation analyses. The demonstrated approach can be extended beyond incorporating thermodynamic features, with input from domain experts used to compile lists of features from other alloy physics, such as diffusion kinetics and microstructure evolution.",1811.01239v1 2020-01-19,Linking electronic structure calculations to generalized stacking fault energies in multicomponent alloys,"The generalized stacking fault energy is a key ingredient to mesoscale models of dislocations. Here we develop an approach to quantify the dependence of generalized stacking fault energies on the degree of chemical disorder in multicomponent alloys. We introduce the notion of a ""configurationally-resolved planar fault"" (CRPF) energy and extend the cluster expansion method from alloy theory to express the CRPF as a function of chemical occupation variables of sites surrounding the fault. We apply the approach to explore the composition and temperature dependence of the unstable stacking fault energy (USF) in binary Mo-Nb alloys. First-principles calculations are used to parameterize a formation energy and CRPF cluster expansion. Monte Carlo simulations show that the distribution of USF energies is significantly affected by chemical composition and temperature. The formalism can be applied to any multicomponent alloy and will enable the development of rigorous models for deformation mechanisms in high-entropy alloys.",2001.06912v1 2019-04-23,Large-area synthesis of continuous two-dimensional MoTexSe2-x alloy films by chemical vapor deposition,"Great achievements have been made in alloying of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), which can allow tunable band gaps for practical applications in optoelectronic devices. However, telluride-based TMDs alloys were less studied due to the difficulties of sample synthesis. Here, in this work we report the large-area synthesis of 2D MoTexSe2-x alloy films with controllable Te composition by a modified alkali metal halides assisted chemical vapor deposition method. The as-prepared films have millimeter-scale transverse size. Raman spectra experiments combining calculated Raman spectra and vibrational images obtained by density functional theory (DFT) confirmed the 2H-phase of the MoTexSe2-x alloys. The A1g mode of MoSe2 shows a significant downshift accompanied by asymmetric broadening to lower wavenumber with increasing value of x, while E12g mode seems unchanged, which were well explained by a phonon confinement model. Our work provides a simple method to synthesize large-scale 2H phase Te-based 2D TMDs alloys for their further applications.",1904.10218v1 2019-10-28,The spin Hall effect of Bi-Sb alloys driven by thermally excited Dirac-like electrons,"We have studied the charge to spin conversion in Bi$_{1-x}$Sb$_x$/CoFeB heterostructures. The spin Hall conductivity (SHC) of the sputter deposited heterostructures exhibits a high plateau at Bi-rich compositions, corresponding to the topological insulator phase, followed by a decrease of SHC for Sb-richer alloys, in agreement with the calculated intrinsic spin Hall effect of Bi$_{1-x}$Sb$_x$ alloy. The SHC increases with increasing thickness of the Bi$_{1-x}$Sb$_x$ alloy before it saturates, indicating that it is the bulk of the alloy that predominantly contributes to the generation of spin current; the topological surface states, if present in the films, play little role. Surprisingly, the SHC is found to increase with increasing temperature, following the trend of carrier density. These results suggest that the large SHC at room temperature, with a spin Hall efficiency exceeding 1 and an extremely large spin current mobility, is due to increased number of Dirac-like, thermally-excited electrons in the $L$ valley of the narrow gap Bi$_{1-x}$Sb$_x$ alloy.",1910.12433v1 2019-10-29,Improvement on corrosion resistance and biocompability of ZK60 magnesium alloy by carboxyl ion implantation,"Magnesium alloys have been considered to be potential biocompatible metallic materials. Further improvement on the anti-corrosion is expected to make this type of materials more suitable for biomedical applications in the fields of orthopedics, cardiovascular surgery and others. In this paper, we introduce a method of carboxyl ion (COOH+) implantation to reduce the degradation of ZK60 Mg alloy and improve its functionality in physiological environment. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) experiments show the formation of a smooth layer containing carbaxylic group, carbonate, metal oxides and hydroxides on the ion implanted alloy surface. Corrosion experiments and in vitro cytotoxicity tests demonstrate that the ion implantation treatment can both reduce the corrosion rate and improve the biocompatibility of the alloy. The promising results indicate that organic functional group ion implantation may be a practical method of improving the biological and corrosion properties of magnesium alloys.",1910.13219v1 2019-06-23,Effect of elastic anisotropy on phase separation in ternary alloys: A phase-field study,"The precipitate shape, size and distribution are crucial factors which determine the properties of several technologically important alloys. Elastic interactions between the inclusions modify their morphology and align them along elastically favourable crystallographic directions. Among the several factors contributing to the elastic interaction energy between precipitating phases, anisotropy in elastic moduli is decisive in the emergence of modulated structures during phase separation in elastically coherent alloy systems. We employ a phase-field model incorporating elastic interaction energy between the misfitting phases to study microstructural evolution in ternary three-phase alloy systems when the elastic moduli are anisotropic. The spatiotemporal evolution of the composition field variables is governed by solving a set of coupled Cahn-Hilliard equations numerically using a semi-implicit Fourier spectral technique. We methodically vary the misfit strains, alloy chemistry and elastic anisotropy to investigate their influence on domain morphology during phase separation. The coherency strains between the phases and alloy composition alter the coherent phase equilibria and decomposition pathways. The degree of anisotropy in elastic moduli modifies the elastic interaction energy between the precipitates depending on the sign and magnitude of relative misfits, and thus determines the shape and alignment of the inclusions in the microstructure.",1906.09637v1 2020-05-20,Can experiment determine the stacking fault energy of metastable alloys?,"Stacking fault energy (SFE) plays an important role in deformation mechanisms and mechanical properties of face-centered cubic (fcc) metals and alloys. In metastable fcc alloys, the SFEs determined from density functional theory (DFT) calculations and experimental methods often have opposite signs. Here, we show that the negative SFE by DFT reflects the thermodynamic instability of the fcc phase relative to the hexagonal close-packed one; while the experimentally determined SFEs are restricted to be positive by the models behind the indirect measurements. We argue that the common models underlying the experimental measurements of SFE fail in metastable alloys. In various concentrated solid solutions, we demonstrate that the SFEs obtained by DFT calculations correlate well with the primary deformation mechanisms observed experimentally, showing a better resolution than the experimentally measured SFEs. Furthermore, we believe that the negative SFE is important for understanding the abnormal behaviors of partial dislocations in metastable alloys under deformation. The present work advances the fundamental understanding of SFE and its relation to plastic deformations, and sheds light on future alloy design by physical metallurgy.",2005.09983v1 2020-08-26,Edge Dislocations Can Control Yield Strength in Refractory Body-Centered-Cubic High Entropy Alloys,"Energy efficiency is motivating the search for new high-temperature metals. Some new body-centered-cubic random multicomponent ""high entropy alloys (HEAs)"" based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here we show, using integrated neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and theory, that the high strength and strength retention of a NbTaVTi alloy and a new high-strength/low-density CrMoNbV alloy are attributable to edge dislocations. This is surprising because plastic-flow in BCC elemental metals and dilute alloys is universally accepted to be controlled by screw dislocations. We use the insight and theory to perform a computationally-guided search over $10^7$ BCC HEAs and identify over $10^6$ possible ultra-strong high-temperature alloy compositions for future exploration.",2008.11671v1 2018-04-25,A multidisciplinary approach to study precipitation kinetics and hardening in an Al-4Cu (wt. %) alloy,"A multidisciplinary approach is presented to analyse the precipitation process in a model Al-Cu alloy. Although this topic has been extensively studied in the past, most of the investigations are focussed either on transmission electron microscopy or on thermal analysis of the processes. The information obtained from these techniques cannot, however, provide a coherent picture of all the complex transformations that take place during decomposition of supersaturated solid solution. Thermal analysis, high resolution dilatometry, (high resolution) transmission electron microscopy and density functional calculations are combined to study precipitation kinetics, interfacial energies, and the effect of second phase precipitates on the mechanical strength of the alloy. Data on both the coherent and semi-coherent orientations of the {\theta}""/Al interface are reported for the first time. The combination of the different characterization and modelling techniques provides a detailed picture of the precipitation phenomena that take place during aging and of the different contributions to the strength of the alloy. This strategy can be used to analyse and design more complex alloys.",1804.09634v1 2019-03-03,Near-Unity Spin Hall Ratio in Ni$_x$Cu$_{1-x}$ Alloys,"We report a large spin Hall effect in the 3$d$ transition metal alloy Ni$_x$Cu$_{1-x}$ for $x\in\left\{ 0.3,0.75\right\} $, detected via the ferromagnetic resonance of a Permalloy (Py = Ni$_{80}$Fe$_{20}$) film deposited in a bilayer with the alloy. A thickness series at $x$ = 0.6, for which the alloy is paramagnetic at room temperature, allows us to determine the spin Hall ratio $\theta_{\rm{SH}}\approx1$, spin diffusion length $\lambda_{\rm{s}}$, spin mixing conductance $G_{\uparrow\downarrow}$, and damping $\alpha_{\rm{SML}}$ due to spin memory loss . We compare our results with similar experiments on Py/Pt bilayers measured using the same method. Ab initio band structure calculations with disorder and spin-orbit coupling suggest an intrinsic spin Hall effect in Ni$_x$Cu$_{1-x}$ alloys, although the experiments here cannot distinguish between extrinsic and intrinsic mechanisms.",1903.00910v2 2019-03-19,Anomalous Ground State in Fe$_{1-x}$Ni$_{x}$ Invar alloys,"This paper reports high resolution X-ray photoelectron spectroscopy (XPS) studies on Fe$_{1-x}$Ni$_x$ (x=0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9) alloys down to 10 K temperature. Core levels and Auger transitions of the alloys except the invar alloy (x=0.4) exhibit no observable temperature induced changes. The invar alloy exhibits changes in the core levels below 20 K temperature that strongly depend on the core level. Such core level dependent changes with temperature were attributed to the precipitation of spin glass like phase below 20 K only in the invar alloy. Ni L$_3$M$_{45}$M$_{45}$ Auger transition also supported such precipitation below 20 K.",1903.08221v3 2019-08-10,"Multielemental single-atom-thick A layers in nanolaminated V2(Sn, A)C (A=Fe, Co, Ni, Mn) for tailoring magnetic properties","Tailoring of individual single-atom-thick layers in nanolaminated materials offers atomic-level control over material properties. Nonetheless, multielement alloying in individual atomic layers in nanolaminates is largely unexplored. Here, we report a series of inherently nanolaminated V2(A'xSn1-x)C (A'=Fe, Co, Ni and Mn, and combinations thereof, with x=1/3) synthesized by an alloy-guided reaction. The simultaneous occupancy of the four magnetic elements and Sn, the individual single-atom-thick A layers in the compound constitute high-entropy-alloy analogues, two-dimensional in the sense that the alloying exclusively occurs in the A layers. V2(A'xSn1-x)C exhibit distinct ferromagnetic behavior that can be compositionally tailored from the multielement A-layer alloying. This two-dimensional alloying provides a structural-design route with expanded chemical space for discovering materials and exploit properties.",1908.03709v1 2019-12-10,Grain refinement and enhancement of critical current density in the V_0.60Ti_0.40 alloy superconductors with Gd addition,"The V-Ti alloys are promising materials as alternate to the commercial Nb-based superconductors for high current-high magnetic field applications. However, the critical current density (J_c) of these alloys are somewhat low due to their low grain-boundary density. We show here that grain refinement of the V-Ti alloys and enhancement of the J_c can be achieved by the addition of Gd into the system, which precipitates as clusters along the grain boundaries. Both the J_c and the pinning force density (F_P) increase with the increasing Gd content up to 1 at. % Gd, where they are more than 20 times higher than those of the parent V_0.60Ti_0.40 alloy. Introduction of Gd into the system also leads to ferromagnetic (FM) correlations, and the alloys containing more than 0.5 at. % Gd exhibit spontaneous magnetization. In spite of the FM correlations, the superconducting transition temperature increases slightly with Gd-addition.",1912.04507v2 2020-03-20,Experimental and theoretical study of tracer diffusion in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys,"Tracer diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured tracer diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the equiatomic CoCrFeMnNi alloy. This is explained by atomistic Monte-Carlo simulations based on a modified embedded-atom potentials, which reveal that local heterogeneities of the atomic configurations around a vacancy cause correlation effects and induce significant deviations from predictions of the random alloy model.",2003.09474v1 2020-06-13,Structural properties of Fe-Ni/Cu/Fe-Ni trilayers on Si (100),"We investigate the structural properties of Fe$_{1-x}$Ni$_x$/Cu/Fe$_{1-x}$Ni$_x$ ( $x=0.5$, non Invar and $x=0.36$, Invar) trilayers deposited on Si~(100)~at room temperature using dc magnetron sputtering technique in ultra high vacuum conditions taking high purity Fe, Ni and Cu metals with Cu layer thickness 4, 6 and 8 nm for each alloy composition. The structure of the alloy films of the trilayers was investigated using x-ray diffraction and the thickness \& roughness of the layers were obtained by x-ray reflectivity measurement. Both the as prepared and annealed trilayers exhibit layered structure. The as deposited Fe-Ni alloy in non Invar trilayer exhibits only fcc structure whereas in Invar alloy it exhibits a mixed fcc and bcc phases. Interestingly after annealing at 425$^0$C in ultra high vacuum, the Invar alloy completely transformed to fcc structure for all Cu thicknesses. In both Invar and non Invar trilayers, the Bragg reflections corresponding to Fe-Ni alloy layers become sharp after annealing. The induced structural transformation in Invar trilayer is explained using enhanced diffusion of Fe and Ni atoms at high temperatures.",2006.07662v1 2020-07-02,Free-standing 2D metals from binary metal alloys,"Recent experiment demonstrated the formation of free-standing Au monolayers by exposing Au-Ag alloy to electron beam irradiation. Inspired by this discovery, we used semi-empirical effective medium theory simulations to investigate monolayer formation in 30 different binary metal alloys composed of late d-series metals Ni, Cu, Pd, Ag, Pt, and Au. In qualitative agreement with the experiment, we find that the beam energy required to dealloy Ag atoms from Au-Ag alloy is smaller than the energy required to break the dealloyed Au monolayer. Our simulations suggest that similar method could also be used to form Au monolayers from Au-Cu alloy and Pt monolayers from Pt-Cu, Pt-Ni, and Pt-Pd alloys.",2007.01291v1 2020-07-22,The origin of jerky dislocation motion in high-entropy alloys,"Dislocations in single-phase concentrated random alloys, including high- entropy alloys (HEAs), repeatedly encounter pinning during glide, resulting in jerky dislocation motion. While solute-dislocation interaction is well understood in conventional alloys, the origin of individual pinning points in concentrated random alloys is a matter of debate. In this work, we investigate the origin of dislocation pinning in the CoCrFeMnNi HEA. In- situ transmission electron microscopy studies reveal wavy dislocation lines and a jagged glide motion under external loading, even though no segregation or clustering is found around Shockley partial dislocations. Atomistic simulations reproduce the jerky dislocation motion and link the repeated pinning to local fluctuations in the Peierls friction. We demonstrate that the density of high local Peierls friction is proportional to the critical stress required for dislocation glide and the dislocation mobility.",2007.11489v3 2020-07-22,An atomistic description of alloys and core shells nanoparticles,"Using the extended discrete interaction model we investigate the tuneabilty of surface plasmon resonance in alloys and core-shell nanoparticles made from silver and gold. We show that the surface plasmon resonance of these alloys and core-shell particles to a large extent follow Vegard's law irrespective of the geometry of the nanoparticle. We show the evolution of the polarizability with size and demonstrate the highly non-linear behaviour of the polarizability with the ratio of the constituents and geometry in alloys and core-shell nanoparticles, with the exception for nanorod alloys. A thorough statistical investigation reveals that there is only a small dependence of the surface plasmon resonance on atomic arrangement and exact distribution in a nanoparticle and that the standard deviation decrease rapidly with the size of the nanoparticles. The physical reasoning for the random distribution algorithm for alloys in discrete interaction models is explained in details and verified by the statistical analysis.",2007.11688v1 2020-09-15,"Alloy Engineering of Polar (Si,Ge)2N2O System for Controllable Second Harmonic Performance","Although silicon oxynitrides are important semiconductors for many practical applications, their potential second-order nonlinear optical (NLO) applications, regardless of balanced or controllable performance, have never been systemically explored. Using the first-principles calculations, in this article, we discover that the sinoite (i.e., typical silicon oxynitride Si2N2O) can simultaneously exhibit wide optical bandgap, strong second-harmonic generation (SHG) effect, and large birefringence, which are further confirmed by our preliminary experimental data. Importantly, we propose that alloying engineering can be further applied to control the balanced NLO properties in the Si2N2O system. Combining first-principles calculations and cluster expansion theory, we demonstrate that alloying Ge into Si2N2O can easily form low formation energy Si2(1-x)Ge2xN2O alloys, which can in turn achieve controllable phase-matching harmonic output with high SHG efficiency at different energy ranges. Therefore, alloy engineering could provide a unique approach to effectively control the balanced NLO performance of Si2(1-x)Ge2xN2O, making this polar alloy system holding potential applications in tunable laser frequency conversion and controllable all-optical devices.",2009.06932v2 2020-10-29,Plasma frequency in doped highly mismatched alloys,"Highly mismatched alloys (HMAs) have band structures strongly modified due to the introduction of the alloying element. We consider HMAs where the isolated state of the alloying element is near the host conduction band, which causes the conduction band to split into two bands. We determine the bulk plasma frequency when the lower-energy band is partially occupied, as by doping, using a semi-analytical method based on a disorder-averaged Green's function. We include the nontrivial effects of interband transitions to the higher-energy band, which limit the plasma frequency to be less than an effective band gap. We show that the distribution of states in the split bands causes plasmons in HMAs to behave differently than plasmons in standard metals and semiconductors. The effective mass of the lower split band $m^*$ changes with alloy fraction, and we find that the plasmon frequency with small carrier concentration $n$ scales with $\sqrt{n}/m^*$ rather than the $\sqrt{n/m^*}$ that is expected in standard materials. We suggest experiments to observe these phenomena. Considering the typical range of material parameters in this group of alloys and taking a realistic example, we suggest that HMAs can serve as highly tunable low-frequency plasmonic materials.",2010.15953v1 2020-12-01,The Benefits of Trace Cu in Wrought Al-Mg Alloys,"The softening and strengthening contributions in pre-deformed and aged Al-Mg-Cu alloys containing 3wt.%Mg and 0.5wt.%Cu are evaluated by a combination of microscopy, mechanical testing and modelling. A refined phenomenological model for the work hardening response, accounting for the separate effects of recovery and precipitation, is shown to be suitable for an unambiguous determination of the precipitation hardening contribution in these alloys. Significantly, it is found that the mechanical response of these alloys is not strongly impacted by Cu content (in the low Cu content regime), pre-deformation level or aging temperature meaning that the alloys are robust with respect to variations in composition. This is interesting from the perspective of alloy design concepts based on `recycling friendly' compositions in applications that include paint-baking.",2012.00277v1 2021-01-14,Neural-networks model for force prediction in multi-principal-element alloys,"Atomistic simulations can provide useful insights into the physical properties of multi-principal-element alloys. However, classical potentials mostly fail to capture key quantum (electronic-structure) effects. We present a deep 3D convolutional neural network (3D CNN) based framework combined with a voxelization technique to design interatomic potentials for chemically complex alloys. We highlight the performance of the 3D CNN model and its efficacy in computing potentials using the medium-entropy alloy TaNbMo. In order to provide insights into the effect of voxel resolution, we implemented two approaches based on the inner and outer bounding boxes. An efficient 3D CNN model, which is as accurate as the density-functional theory (DFT) approach, for calculating potentials will provide a promising schema for accurate atomistic simulations of structure and dynamics of general multi-principle element alloys.",2101.05867v2 2021-01-29,Surface lattice Green's functions for high-entropy alloys,"We study the surface elastic response of pure Ni, the random alloy FeNiCr and an average FeNiCr alloy in terms of the surface lattice Green's function. We propose a scheme for computing per-site Green's function and study their per-site variations. The average FeNiCr alloy accurately reproduces the mean Green's function of the full random alloy. Variation around this mean is largest near the edge of the surface Brillouin-zone and decays as $q^{-2}$ with wavevector $q$ towards the $\Gamma$-point. We also present expressions for the continuum surface Green's function of anisotropic solids of finite and infinite thickness and show that the atomistic Green's function approaches continuum near the $\Gamma$-point. Our results are a first step towards efficient contact calculations and Peierls-Nabarro type models for dislocations in high-entropy alloys.",2101.12519v1 2021-02-26,Data Analytics Approach to Predict High-Temperature Cyclic Oxidation Kinetics of NiCr-based Alloys,"Although of practical importance, there is no established modeling framework to accurately predict high-temperature cyclic oxidation kinetics of multi-component alloys due to the inherent complexity. We present a data analytics approach to predict the oxidation rate constant of NiCr-based alloys as a function of composition and temperature with a highly consistent and well-curated experimental dataset. Two characteristic oxidation models, i.e., a simple parabolic law and a statistical cyclic-oxidation model, have been chosen to numerically represent the high-temperature oxidation kinetics of commercial and model NiCr-based alloys. We have successfully trained machine learning (ML) models using highly ranked key input features identified by correlation analysis to accurately predict experimental parabolic rate constants (kp). This study demonstrates the potential of ML approaches to predict oxidation kinetics of alloys over a wide composition and temperature ranges. This approach can also serve as a basis for introducing more physically meaningful ML input features to predict the comprehensive cyclic oxidation behavior of multi-component high-temperature alloys with proper constraints based on the known underlying mechanisms.",2102.13261v1 2021-04-12,CALPHAD-informed phase-field modeling of grain boundary microchemistry and precipitation in Al-Zn-Mg-Cu alloys,"The grain boundary (GB) microchemistry and precipitation behaviour in high-strength Al-Zn-Mg-Cu alloys has an important influence on their mechanical and electrochemical properties. Simulation of the GB segregation, precipitation, and solute distribution in these alloys requires an accurate description of the thermodynamics and kinetics of this multi-component system. CALPHAD databases have been successfully developed for equilibrium thermodynamic calculations in complex multi-component systems, and in recent years have been combined with diffusion simulations. In this work, we have directly incorporated a CALPHAD database into a phase-field framework, to simulate, with high fidelity, the complex kinetics of the non-equilibrium GB microstructures that develop in these important commercial alloys during heat treatment. In particular, the influence of GB solute segregation, GB diffusion, precipitate number density, and far-field matrix composition, on the growth of a population of GB precipitates, was systematically investigated in a model Al-Zn-Mg-Cu alloy of near AA7050 composition. The simulation results were compared with scanning transmission electron microscopy and atom probe tomography characterisation of alloys of the similar composition, with good agreement.",2104.05791v1 2021-04-15,Optimization of High Entropy Alloy Catalyst for Ammonia Decomposition and Ammonia Synthesis,"The successful synthesis of high entropy alloy (HEA) nanoparticles, a long-sought goal in materials science, opens a new frontier in materials science with applications across catalysis, electronics, structural alloys, and energetic materials. Recently, a Co25Mo45Fe10Ni10Cu10 HEA made of earth-abundant elements was shown to have a high catalytic activity for ammonia decomposition, which rivals that of state-of-the-art, but prohibitively expensive, ruthenium catalyst. Using a computational approach based on first-principles calculations in conjunction with data analytics and machine learning, we build a model to rapidly compute the adsorption energy of H, N, and NHx (x=1,3) species on CoMoFeNiCu alloy surfaces with varied alloy compositions and atomic arrangement. We show that the 25/45 Co/Mo ratio identified experimentally as the most active composition for ammonia decomposition increases the likelihood that the surface adsorbs nitrogen equivalently to that of ruthenium while at the same time interacting moderately strongly with intermediates. Our study underscores the importance of computational modeling and machine learning to identify and optimize HEA alloys across their near-infinite materials design space.",2104.07827v2 2021-05-06,Low temperature annealing method for fabricating alloy nanostructures and metasurfaces: Unlocking a novel degree of freedom,"The material and exact shape of a nanostructure determine its optical response, which is especially strong for plasmonic metals. Unfortunately, only a very few plasmonic metals are available, which limits the spectral range where these strong optical effects can be utilized. Alloying different plasmonic metals can overcome this limitation, at the expense of using a high temperature alloying process, which adversely destroys the nanostructure shape. Here, we develop a low temperature alloying process at only 300{\deg}C and fabricate Au-Ag nanostructures with a broad diversity of shapes, aspect ratios and stoichiometries. EDX and XPS analyses confirm the homogeneous alloying through the entire sample. Varying the alloy stoichiometry tunes the optical response of the nanostructure and controls spectral features such as Fano resonances. Binary metasurfaces that combine nanostructures with different stoichiometries are fabricated using multiple-step electron beam lithography, and their optical function as hologram or Fresnel zone plate is demonstrated at the visible wavelength of 532 nm. This low temperature annealing technique provides a versatile and cost-effective way of fabricating complex Au-Ag nanostructures with arbitrary stoichiometry.",2105.02461v1 2021-05-11,Exploring the Correlation between Solvent Diffusion and Creep Resistance of Mg-Ga HCP Alloys from High Throughput Liquid-Solid Diffusion Couple,"The liquid-solid diffusion couple technique, supported by phenomenological analysis and nano-indentation tests, is proposed on account of the relatively low melting points of Mg to explore the diffusion mobility and creep deformation. The potential of this strategy is demonstrated in Mg-Ga hcp alloys where Ga solute (i.e. impurity) and Mg solvent diffusions in hcp Mg-Ga alloys were both unveiled. It was followed by mapping the compressive creep behavior via nanoindentation along the composition arrays within the same Mg-Ga couple sample. The compressive creep resistance of Mg-Ga hcp alloys increased with the Ga content, and this enhancement was similar to the one found in Mg-Zn alloys and superior to the one reported in Mg-Al alloys though Al is a slower impurity diffuser in hcp-Mg than Zn and Ga. Thereby, the solvent diffusion and its variation with the composition, rather than the solute diffusion, was suggested to govern the creep properties at high temperatures and low stresses.",2105.05096v1 2021-05-31,Aluminium Alloy Design and Discovery using Machine Learning,"The traditional design and development of metallic alloys has taken a hill-climbing approach to date, with incremental advances. Throughout the last century, aluminium (Al) alloy design has been essentially empirical and iterative, based on lessons learned from in service use and human experience. Incremental alloy development is costly, slow, and doesn't fully harness the data that exists in the field of Al-alloy metallurgy. In the present work, an attempt has been made to utilise a data science approach to develop a machine learning (ML) model for Al-alloy design. An objective-optimisation process has also been developed, to exploit the ML model, for user experience and practical application. A successful model was developed and presented herein, along with the open-access software.",2105.14806v2 2021-06-23,First-principles study of the robust superconducting state of NbTi alloys under ultrahigh pressures,"A recent experiment reported that robust superconductivity appears in NbTi alloys under ultrahigh pressures with an almost constant superconducting $T_c$ of ~19 K from 120 to 261.7 GPa [J. Guo et al., Adv. Mater. 31, 1807240 (2019)], which is very rare among the known superconductors. We investigate the origin of this novel superconducting behavior in NbTi alloys based on density functional theory and density functional perturbation theory calculations. Our results indicate that the pressure tends to transform NbTi alloys from a random phase to a uniformly ordered crystal phase, and the exotic robust superconductivity of NbTi alloys can still be understood in the framework of BCS theory. The Nb element in NbTi alloys plays a dominant role in the superconductivity at low pressure, while the NbTi crystal with an alternative and uniform Nb and Ti atomic arrangement may be responsible for the stable superconductivity under high pressures. The robust superconducting transition temperature of NbTi under ultrahigh pressure can be explained by a synergistic effect of the enhanced phonon frequency, the modestly reduced total electron-phonon coupling, and the pressure-dependent screened Coulomb repulsion.",2106.12371v1 2021-11-05,Towards Stacking Fault Energy Engineering in FCC High Entropy Alloys,"Stacking Fault Energy (SFE) is an intrinsic alloy property that governs much of the plastic deformation mechanisms observed in fcc alloys. While SFE has been recognized for many years as a key intrinsic mechanical property, its inference via experimental observations or prediction using, for example, computationally intensive first-principles methods is challenging. This difficulty precludes the explicit use of SFE as an alloy design parameter. In this work, we combine DFT calculations (with necessary configurational averaging), machine-learning (ML) and physics-based models to predict the SFE in the fcc CoCrFeMnNiV-Al high-entropy alloy space. The best-performing ML model is capable of accurately predicting the SFE of arbitrary compositions within this 7-element system. This efficient model along with a recently developed model to estimate intrinsic strength of fcc HEAs is used to explore the strength-SFE Pareto front, predicting new-candidate alloys with particularly interesting mechanical behavior.",2111.03591v1 2022-01-20,Coexistence of two types of short-range order in SiGeSn medium-entropy alloys,"Short-range chemical order (SRO) has been recently demonstrated to play a decisive role in modulating a wide range of physical properties in medium-entropy alloy (MEA) and high-entropy alloy (HEA). The enormous configurational space of these alloys implies multiple forms of SRO are likely to develop concurrently but such structural diversity has not been reported. Here we show, through extensive {\em ab initio}-based sampling study, that SiGeSn medium-entropy alloys spontaneously develop two distinct forms of SRO. Remarkably, the two types of SROs, which carry different energies, distinct degrees of local ordering, and dissimilar electronic structures, are found to co-exist in a wide range of compositions of SiGeSn alloys. The co-existence of two SROs is rationalized through their virtual degeneracy of thermodynamic stability, due to the subtle balance in the change of enthalpy and configurational entropy upon the transformation between the two SROs. Such co-existence of SROs thus suggests an inherent structural heterogeneity, a diffuse electronic structure, and a new route for band engineering in SiGeSn MEA. More generally, our finding indicates the possible ubiquity of the co-existence of multiple forms of SRO in a broad range of MEAs and HEAs, which has profound implications on their diverse physical properties.",2201.08256v1 2022-08-24,Low-temperature ordering in a substitutional alloy with injecting nonequilibrium vacancies: The FePt case,"Achieving the compositionally ordered state in a substitutional alloy of two or more species can often be even critical for improving its functional properties. To produce a highly ordered alloy, a longtime high-temperature (up to T=1000 K) treatment of the alloy is typically necessary because of insufficient vacancy concentration (c_v) and their mobility. However, such processing affects the morphology and complicates the technology of functional alloys. We show theoretically that the ordering in the practically important FePt system (Fe_xPt_1-x with x being close to 0.5) is already achievable at T=450 K for reasonable times t<10^3 s due to frozen nonequilibrium vacancies. Our simulation is based on the Dienes equation for relaxation of the long-range order parameter (S), with taking additionally into account that the ordering kinetics in the alloy is mediated by vacancies. Importantly, the results of such simulation are in good agreement with previous experimental data on the ordering kinetics. We also find that nanosecond laser pulses can be employed to achieve a sufficient level of c_v=10^-5 for effective low-temperature ordering.",2208.11720v3 2022-10-07,Radiation-resistant aluminium alloy for space missions in the extreme environment of the solar system,"Future human-based exploration of our solar system requires the invention of materials that can resist harsh environments. Age-hardenable aluminium alloys would be attractive candidates for structural components in long-distance spacecrafts, but their radiation resistance to solar energetic particles is insufficient. Common hardening phases dissolve and displacement damage occurs in the alloy matrix, which strongly degrades properties. Here we present an alloy where hardening is achieved by T-phase, featuring a giant unit cell and highly-negative enthalpy of formation. The phase shows record radiation survivability and can stabilize an ultrafine-grained structure upon temperature and radiation in the alloy, therby successfully preventing displacement damage to occur. Such concept can be considered ideal for the next-generation space materials and the design of radiation resistant alloy.",2210.03397v3 2022-12-31,Investigating representation schemes for surrogate modeling of High Entropy Alloys,"The design of new High Entropy Alloys that can achieve exceptional mechanical properties is presently of great interest to the materials science community. However, due to the difficulty of designing these alloys using traditional methods, machine learning has recently emerged as an essential tool. Particularly, the screening of candidate alloy compositions using surrogate models has become a mainstay of materials design in recent years. Many of these models use the atomic fractions of the alloying elements as inputs. However, there are many possible representation schemes for encoding alloy compositions, including both unstructured and structured variants. As the input features play a critical role in determining surrogate model performance, we have systematically compared these representation schemes on the basis of their performance in single-task deep learning models and in transfer learning scenarios. The results from these tests indicate that compared to the unstructured and randomly ordered schemes, chemically meaningful arrangements of elements within spatial representation schemes generally lead to better models. However, we also observed that tree-based models using only the atomic fractions as input were able to outperform these models in transfer learning.",2301.00179v1 2023-03-08,Atomic Representations of Local and Global Chemistry in Complex Alloys,"The exceptional properties observed in complex concentrated alloys (CCAs) arise from the interplay between crystalline order and chemical disorder at the atomic scale, complicating a unique determination of properties. In contrast to conventional alloys, CCA properties emerge as distributions due to varying local chemical environments and the specific scale of measurement. Currently there are few ways to quantitatively define, track, and compare local alloy compositions (versus a global label, i.e. equiatomic) contained in a CCA. Molecular dynamics is used here to build descriptive metrics that connect a global alloy composition to the diverse local alloy compositions that define it. A machine-learned interatomic potential for MoNbTaTi is developed and we use these metrics to investigate how property distributions change with excursions in global-local composition space. Short-range order is examined through the lens of local chemistry for the equiatomic composition, demonstrating stark changes in vacancy formation energy with local chemistry evolution.",2303.04311v3 2023-05-20,A Computational Approach for Mapping Electrochemical Activity of Multi-Principal Element Alloys,"Multi principal element alloys (MPEAs) comprise a unique class of metal alloys. MPEAs have been demonstrated to possess several exceptional properties, including, as most relevant to the present study, a high corrosion resistance. In the context of MPEA design, the vast number of potential alloying elements and the staggering number of elemental combinations favours a computational alloy design approach. In order to computationally assess the prospective corrosion performance of MPEA, an approach was developed in this study. A density functional theory (DFT) based Monte Carlo method was used for the development of MPEA structure, with the AlCrTiV alloy used as a model. High-throughput DFT calculations were performed to create training datasets for surface activity towards different adsorbate species: O2-, Cl- and H+. Machine learning (ML) with combined representation was then utilised to predict the adsorption and vacancy energies as descriptors for surface activity. The capability of the combined computational methods of MC, DFT and ML, as a virtual electrochemical performance simulator for MPEAs was established and may be useful in exploring other MPEAs.",2305.12059v1 2023-06-29,Structure-Dynamics Relationship in Al-Mg-Si Liquid Alloys,"Enhancing properties and performances of aluminium alloys by a control of their solidification is pivotal in automotive and aerospace industries. The fundamental role of the structure-diffusion relationship is investigated for Al-Mg-Si liquid alloys taken as a prototype of Al-6xxx. For this purpose, first principles-based molecular dynamics simulations were performed for various Si and Mg content for Al-rich compositions, including the binary alloy counterparts. Results indicate that Mg and/or Si in alloys create a more compact ordering around Al than in pure Al, lowering diffusion. Mg promotes icosahedral short-range order, while Si displays a preference towards cubic local ordering, impacting diffusion based on their respective content. It suggests a mechanism whereby an increase in Mg content generally lowers the diffusion of each species, whereas an increase in Si content enhances their diffusion, providing insights for future alloy design.",2306.17264v1 2023-12-07,Integrated Design of Aluminum-Containing High-entropy Refractory B2 Alloys with Synergy of High Strength and Ductility,"Refractory high-entropy alloys, RHEAs, are promising high-temperature structural materials. Their large compositional space poses great design challenges for phase control and high strength-ductility synergy. The present research pioneers using integrated high-throughput machine learning with Monte Carlo simulations to effectively navigate phase-selection and mechanical-properties predictions, developing aluminum-containing RHEAs in single-phase ordered B2 alloys demonstrating both high strength and ductility. These aluminum-containing RHEAs achieve remarkable mechanical properties, including compressive yield strengths up to 1.6 GPa, fracture strains exceeding 50 percent, and significant high-temperature strength retention. They also demonstrate a tensile yield strength of 1.1 GPa with a tension ductility of 6.3 percent. Besides, we identify a valence-electron-count domain for alloy brittleness with the explanation from density-functional theory and provide crucial insights into elements' influence on atomic ordering and mechanical performance. The work sets forth a strategic blueprint for high-throughput alloy design and reveals fundamental principles that govern the mechanical properties of advanced structural alloys.",2312.04708v1 2024-01-30,Empirical tight-binding method for large-supercell simulations of disordered semiconductor alloys,"We analyze and present applications of a recently proposed empirical tight-binding scheme for investigating the effects of alloy disorder on various electronic and optical properties of semiconductor alloys, such as the band gap variation, the localization of charge carriers, and the optical transitions. The results for a typical antimony-containing III-V alloy, GaAsSb, show that the new scheme greatly improves the accuracy in reproducing the experimental alloy band gaps compared to other widely used schemes. The atomistic nature of the empirical tight-binding approach paired with a reliable parameterization enables more detailed physical insights into the effects of disorder in alloyed materials.",2401.16951v1 2024-01-31,Investigation of Microstructure and Corrosion Resistance of Ti-Al-V Titanium Alloys Obtained by Spark Plasma Sintering,"The research results of the microstructure and corrosion resistance of Ti and Ti-Al-V Russian industrial titanium alloys obtained by spark plasma sintering (SPS) are described. Investigations of the microstructure, phase composition, hardness, tensile strength, electrochemical corrosion resistance and hot salt corrosion of Ti-Al-V titanium alloy specimens were carried out. It was shown that the alloy specimens have a uniform highly dense microstructure and high hardness values. The studied alloys also have high resistance to electrochemical corrosion during tests in acidic aqueous solution causing the intergranular corrosion as well as high resistance to the hot salt corrosion. The assumption that the high hardness of the alloys as well as the differences in the corrosion resistance of the central and lateral parts of the specimens are due to the diffusion of carbon from the graphite mold into the specimen surface was suggested.",2401.17941v1 2024-02-09,Right or Wrong -- Understanding How Novice Users Write Software Models,"Writing declarative models has numerous benefits, ranging from automated reasoning and correction of design-level properties before systems are built, to automated testing and debugging of their implementations after they are built. Alloy is a declarative modeling language that is well-suited for verifying system designs. A key strength of Alloy is its scenario-finding toolset, the Analyzer, which allows users to explore all valid scenarios that adhere to the model's constraints up to a user-provided scope. However, even with visualized scenarios, it is difficult to write correct Alloy models. To address this, a growing body of work explores different techniques for debugging Alloy models. In order to develop and evaluate these techniques in an effective manor, this paper presents an empirical study of over 97,000 models written by novice users trying to learn Alloy. We investigate how users write both correct and incorrect models in order to produce a comprehensive benchmark for future use as well as a series of observations to guide debugging and educational efforts for Alloy model development.",2402.06624v3 2024-02-29,Searching for magnetically hard monoborides (and finding a few): A first-principles investigation,"New hard magnetic materials with zero or low rare earth content are in demand due to the high prices of the rare earth metals. Among the candidates for such materials, we consider MnB, FeB and their alloys, because previous experiments suggest that FeB has a relatively high magnetic hardness of about 0.83 at room temperature. Using first-principles calculations, we examine the full range of alloys from CrB, through MnB, FeB, to CoB. Furthrmore, we consider alloys of MnB and FeB with substitutions of 3$d$, 4$d$ and 5$d$ transition metals. For the above ninety compositions, we determine magnetic moment, magnetocrystalline anisotropy energy and magnetic hardness. For (Fe-Co)B alloys, the calculated values of magnetic hardness exceed five, which is an exceptionally high. While these values are inflated by the virtual crystal approximation used, we still expect actual magnetic hardnesses well above unity. Furthermore, we classify considered MnB alloys substituted with transition metals as magnetically soft or semi-hard and FeB alloys with Sc, Ti, V, Zr, Nb, Mo, Hf, Ta or W as magnetically hard (with magnetic hardness exceeding unity).",2403.00138v1 2024-03-25,Enhanced mobility of ternary InGaAs quantum wells through digital alloying,"High In content InGaAs quantum wells (In $\geq$ 75%) are potentially useful for topological quantum computing and spintronics applications. In high mobility InGaAs quantum wells, alloy disorder scattering is a limiting factor. In this report, we demonstrate that by growing the InGaAs quantum wells as a digital alloy, or a short period superlattice, we can reduce the alloy disorder scattering within the quantum well and increase the peak 2 K electron mobility to 545,000 cm^2/V s, which is the highest reported mobility for high In content InGaAs quantum wells to the best of the authors' knowledge. Our results demonstrate that the digital alloy approach can be used to increase the mobility of quantum wells in random alloy ternary materials.",2403.17166v2 2024-03-31,First Principles Studies of Stacking Fault Energies in Ternary Magnesium Alloys,"Magnesium (Mg) alloys have emerged as promising materials due to their low density and high strength-to-weight ratio, offering a wide range of applications across multiple industries. Nevertheless, the inherent brittleness of Mg alloys poses a significant hurdle, necessitating innovative approaches to enhance their mechanical performance. Among the various strategies, manipulating stacking fault energy (SFE) has been a key focus, although primarily within the realm of binary alloys. This study investigates SFE in Mg alloys, focusing on ternary compositions. Utilizing first-principles DFT calculations, we analyze solute interactions and their influence on SFE, particularly in Mg-Al-X and Mg-Zn-X configurations. Predictive models are developed for estimating SFE effects, revealing solute pairs that mimic rare earth elements and show potential for improved ductility. The findings contribute to fundamental insights into Mg alloy behavior, offering practical directions for designing advanced materials with superior mechanical properties.",2404.00564v1 2012-09-29,The effect of precipitation on strength and ductility in a Mg-Zn-Y alloy,"The effect of pre-ageing deformation on the size and distribution of beta-prime precipitates and subsequently on the resulting strength and ductility have been measured in a Mg-3.0at.%Zn-0.5at.%Y alloy. The alloy was extruded and then subjected to a T8 heat treatment comprised of a solution-treatment, cold-work and artificial ageing. Extrusion was used to introduce texture, ensuring that deformation occurred via slip rather than twinning. Samples were subjected to controlled uniaxial deformation and then isothermally aged to peak hardness. Precipitate length, diameter and number density were measured and evaluated in terms of the strength and ductility of the alloy. The nucleation of the beta-prime precipitates in peak-aged condition without pre-ageing deformation (i.e.T6 treatment) was poor, with only 0.5% volume fraction, compared to approximately 3.5% in T6 treated binary Mg-3.0at.%Zn alloy. The microstructure of the Mg-Zn-Y alloy was less refined, with larger diameter precipitates and lower beta-prime number densities compared to a binary Mg-3.0at.%Zn alloy. Deformation to 5% plastic strain increased the volume fraction of beta-prime precipitates to approximately 2.3% and refined the beta-prime precipitate length and diameter. The combination of these effects increased the yield strength after isothermal ageing from 217MPa (0% cold-work) to 287 MPa (5% cold-work). The yield stress increased linearly with reciprocal interparticle spacing on the basal and prismatic planes and the alloy showed similar strengthening against basal slip to Mg-Zn. The elongation increased linearly with particle spacing. The ductility of Mg-Zn-Y alloys was similar to that of Mg-Zn for equivalently spaced particles.",1210.0079v1 2013-04-18,Alloying effect on the ideal tensile strength of ferromagnetic and paramagnetic bcc iron,"Using \emph{ab initio} alloy theory formulated within the exact muffin-tin orbitals theory in combination with the coherent potential approximation, we investigate the ideal tensile strength (ITS) in the $[001]$ direction of bcc ferro-/ferrimagnetic (FFM) and paramagnetic (PM) Fe$_{1-x}M_{x}$ ($M=$ Al, V, Cr, Mn, Co, or Ni) random alloys. The ITS of ferromagnetic (FM) Fe is calculated to be $12.6$\,GPa, in agreement with available data, while the PM phase turns out to posses a significantly lower value of $0.7\,$GPa. Alloyed to the FM matrix, we predict that V, Cr, and Co increase the ITS of Fe, while Al and Ni decrease it. Manganese yields a weak non-monotonic alloying behavior. In comparison to FM Fe, the alloying effect of Al and Co to PM Fe is reversed and the relative magnitude of the ITS can be altered more strongly for any of the solutes. All considered binaries are intrinsically brittle and fail by cleavage of the $(001)$ planes under uniaxial tensile loading in both magnetic phases. We show that the previously established ITS model based on structural energy differences proves successful in the PM Fe-alloys but is of limited use in the case of the FFM Fe-based alloys. The different performance is attributed to the specific interplay between magnetism and volume change in response to uniaxial tension. We establish a strong correlation between the compositional effect on the ITS and the one on the shear elastic constant $C'$ for the PM alloys and briefly discuss the relation between hardenability and the ITS.",1304.5129v2 2020-11-12,Alloying behavior of wide band gap alkaline-earth chalcogenides,"Alloying is a powerful tool for tuning materials that facilitates the targeted design of desirable properties for a variety of applications. In this work, we provide a comprehensive investigation of the synthetic accessibility and electronic properties of nine alkaline-earth chalcogenide anion alloys (CaS$_{1-x}$O$_x$, CaS$_{1-x}$Se$_x$, CaS$_{1-x}$Te$_x$, SrS$_{1-x}$O$_x$, SrS$_{1-x}$Se$_x$, SrS$_{1-x}$Te$_x$, MgS$_{1- x}$O$_x$, MgS$_{1-x}$Se$_x$, and MgS$_{1-x}$Te$_x$). We show that isostructural alloying within the rock salt structure is favored for all systems except MgS$_{1-x}$Te$_x$, which is predicted to be a heterostructural alloy between the rock salt and wurtzite structures. Alloys of S and Se are shown to be readily accessible for all cations with low miscibility critical temperatures, enabling continuous tuning of electronic properties across this composition space. Alloys of S and Te have higher critical temperatures but may be accessible through non-equilibrium synthesis strategies and are predicted here to have desirable electronic properties for optoelectronics with wide band gaps and lower effective masses than alloys of S and Se. Anion alloying in MgS$_{1-x}$Te$_x$ stabilizes the wurtzite structure across a significant fraction of composition space, which may make it of particular interest as a transparent conducting material due to its lower effective masses and a higher band gap than the rock salt structure. Zero-point corrected random phase approximation (RPA) energies were computed to resolve the small polymorph energy differences of the Mg compounds and are shown to be critical for accurately describing the thermodynamic properties of the corresponding alloys.",2011.06628v1 2023-08-15,Electronic and optical properties of boron containing GaN alloys: The role boron atom clustering,"Boron (B) containing III-nitride materials, such as wurtzite (B,Ga)N alloys, have recently attracted significant interest to tailor the electronic and optical properties of optoelectronic devices operating in the visible and ultraviolet spectral range. However, the growth of high quality samples is challenging and B atom clustering is often observed in (B,Ga)N alloys. To date, fundamental understanding of the impact of such clustering on electronic and optical properties of these alloys is sparse. In this work we employ density functional theory (DFT) in the framework of the meta generalized gradient approximation (modified Becke Johnson (mBJ) functional) to provide insight into this question. We use mBJ DFT calculations, benchmarked against state-of-the-art hybrid functional DFT, on (B,Ga)N alloys in the experimentally relevant B content range of up to 7.4%. Our results reveal that B atom clustering can lead to a strong reduction in the bandgap of such an alloy, in contrast to alloy configurations where B atoms are not forming clusters, thus not sharing nitrogen (N) atoms. We find that the reduction in bandgap is linked mainly to carrier localization effects in the valence band, which stem from local strain and polarization field effects. However, our study also reveals that the alloy microstructure of a B atom cluster plays an important role: B atom chains along the wurtzite c-axis impact the electronic structure far less strongly when compared to a chain formed within the c-plane. This effect is again linked to local polarization field effects and the orbital character of the involved valence states in wurtzite BN and GaN. Overall, our calculations show that controlling the alloy microstructure of (B,Ga)N alloys is of central importance when it comes to utilizing these systems in future optoelectronic devices with improved efficiencies.",2308.07759v1 2002-09-11,"Exchange bias in [Co2MnGe/Au],[Co2MnGe/Cr] and [Co2MnGe/Cu2MnAl] multilayers","We report structural and magnetic properties of multilayers composed of thin layers of the half metallic ferromagnetic Heusler compound Co2MnGe and layers of Au, Cr and the Heusler compound Cu2MnAl. The hysteresis loops measured at low temperatures reveal the existence of an exchange bias field HEB in all of these multilayers. For the [Co2MnGe/Au] multilayer system HEB is largest reaching up to 1 kOe at a temperature of 2 K. We characterize the exchange bias phenomenon in detail and show that it originates from a spin glass type of magnetic order for a thin interlayer at the interfaces. We discuss the results in the light of different models proposed for the explanation of the exchange bias effect.",0209259v1 2003-04-15,First-principles study of lattice instabilities in the ferromagnetic martensite Ni$_2$MnGa,"The phonon dispersion relations and elastic constants for ferromagnetic Ni$_2$MnGa in the cubic and tetragonally distorted Heusler structures are computed using density-functional and density-functional perturbation theory within the spin-polarized generalized-gradient approximation. For $0.9 6at%. The critical temperatures are not significantly increased by the P alloying.",0908.0063v2 2010-01-11,Calculation of the P-T phase diagram and tendency toward decomposition in equiatomic TiZr alloy,"Electronic, structural and thermodynamic properties of the equiatomic alloy TiZr are calculated within the electron density functional theory and the Debye-Gruneisen model. The calculated values of the lattice parameters a and c/a agree well with the experimental data for the alpha, omega and beta phases. The omega phase is shown to be stable at atmospheric pressure and low temperatures; it remains energetically preferable up to T=600K. The alpha phase of the TiZr alloy becomes stable in the range 600K_{Al}$ directions ($C3$). We also analyze the association of quenched-in dislocations with clustering phenomena. The results of this work can open a new frontier in advancing alloy-process-property design for commercially-important age-hardenable Al alloys.",1407.6412v1 2014-07-31,First principles prediction of structural and electronic properties of TlxIn(1-x)N alloy,"Structural and electronic properties of zinc blende TlxIn(1-x)N alloy have been evaluated from first principles. The band structures have been obtained within the density functional theory (DFT), the modified Becke-Johnson (MBJLDA) approach for the exchange-correlation potential, and fully relativistic pseudopotentials. The calculated band-gap dependence on Tl content in this hypothetical alloy exhibits a linear behaviour up to the 25 % of thalium content where its values become close to zero. In turn, the split-off energy at the Gamma point of the Brillouin zone, related to the spin-orbit coupling, is predicted to be comparable in value with the band-gap for relatively low thalium contents of about 5 %. These findings suggest TlxIn(1-x)N alloy as a promising material for optoelectronic applications. Furthermore, the band structure of TlN reveals some specific properties exhibited by topological insulators.",1407.8424v1 2015-02-24,Accommodation of Tin in Tetragonal ZrO2,"Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The $Sn_{Zr}^{\times}$ site defect was shown to be dominant across most oxygen partial pressures, with $Sn_{Zr}^{""}$ charge compensated by fully charged oxygen vacancies occurring at partial pressures below $10^{-31}$ atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which $Sn_{Zr}^{""}$ is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys.",1502.06883v1 2015-03-04,Structural and magnetic properties of MnCo1-xFexSi alloys,"The crystal structures, martensitic structural transitions and magnetic properties of MnCo1-xFexSi (0 <= x <= 0.50) alloys were studied by differential scanning calorimetry (DSC), x-ray powder diffraction (XRD) and magnetic measurements. In high-temperature paramagnetic state, the alloys undergo a martensitic structural transitions from the Ni2In-type hexagonal parent phase to the TiNiSi-type orthorhombic martensite. Both the martensitic transition temperature (TM) and Curie temperatures of martensite (T_C^M) decrease with increasing Fe content. The introduced Fe atoms establish ferromagnetic (FM) coupling between Fe-Mn atoms and destroy the double spiral antiferromagnetic (AFM) coupling in MnCoSi compound, resulting in a magnetic change in the martensite phase from a spiral AFM state to a FM state. For the alloys with x = 0.10, 0.15 and 0.20, a metamagnetic transition was observed in between the two magnetic states. A magnetostructural phase diagram of MnCo1-xFexSi (0 <= x <= 0.50) alloys was proposed.",1503.01226v1 2015-03-09,Anharmonicity changes the solid solubility of an alloy at high temperatures,"We have developed a method to accurately and efficiently determine the vibrational free energy as a function of temperature and volume for substitutional alloys from first principles. Taking Ti$_{1-x}$Al$_x$N alloy as a model system, we calculate the isostructural phase diagram by finding the global minimum of the free energy, corresponding to the true equilibrium state of the system. We demonstrate that the anharmonic contribution and temperature dependence of the mixing enthalpy have a decisive impact on the calculated phase diagram of a Ti$_{1-x}$Al$_x$N alloy, lowering the maximum temperature for the miscibility gap from 6560 K to 2860 K. Our local chemical composition measurements on thermally aged Ti$_{0.5}$Al$_{0.5}$N alloys agree with the calculated phase diagram.",1503.02459v2 2015-04-14,Electron mobility in few-layer MoxW1-xS2,"In this letter, we theoretically study the electron mobility in few-layer MoxW1-xS2 as limited by various scattering mechanisms. The room temperature energy-dependent scattering times corresponding to polar longitudinal optical (LO) phonon, alloy and background impurity scattering mechanisms are estimated based on the Born approximation to Fermi's Golden rule. The contribution of individual scattering rates is analyzed as a function of 2D electron density as well as of alloy composition in MoxW1-xS2. While impurity scattering limits the mobility for low carrier density (<2x1012 cm-2), LO polar phonon scattering is the dominant mechanism for high electron densities. Alloy scattering is found to play a non-negligible role for 0.5 < x < 0.7 in MoxW1-xS2. The LO phonon limited and impurity limited mobilities show opposing trends with respect to alloy mole fraction. The understanding of electron mobility in MoxW1-xS2 presented here is expected to aid the design and realization of hetero-structures and devices based on alloys of MoS2 and WS2.",1504.03593v1 2015-05-23,Debye temperature of nanocrystalline Fe-Cr alloys obtained by mechanical alloying,"A series on nanocrystalline Fe100-xCrx alloys prepared by mechanical alloying was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM) and M\""ossbauer spectroscopy (MS) techniques. XRD and SEM were used to structurally characterize the samples whereas MS permitted phase analysis as well as determination of the Debye temperature, Theta_D. Concerning the latter, an enhancement relative to bulk Theta_D-values was revealed in the range of ca. 40 < x <50. In a sample of Fe55.5Cr44.5 two phases were detected viz. (1) crystalline and magnetic with Theta_D=572(56) K and (2) amorphous and paramagnetic with Theta_D=405(26) K.",1505.06374v1 2015-11-27,First-Principles prediction of the deformation modes in austenitic Fe-Cr-Ni alloys,"First-principles alloy theory is used to establish the $\gamma$-surface of Fe-Cr-Ni alloys as function of chemical composition and temperature. The theoretical stacking fault energy (SFE) versus chemistry and temperature trends agree well with experiments. Combining our results with the recent plasticity theory based on the $\gamma$-surface, the stacking fault formation is predicted to be the leading deformation mechanism for alloys with effective stacking fault energy below about 18 mJ m$^{-2}$. Alloys with SFE above this critical value show both twinning and full slip at room temperature and twinning remains a possible deformation mode even at elevated temperatures, in line with observations.",1511.08623v1 2015-12-20,Thermal vacancies in random alloys in the single-site mean-field approximation,"A formalism for the vacancy formation energies in random alloys within the single-site mean-filed approximation, where vacancy-vacancy interaction is neglected, is outlined. It is shown that the alloy configurational entropy can substantially reduce the concentration of vacancies at high temperatures. The energetics of vacancies in random Cu-0.5Ni-0.5 alloy is considered as a numerical example illustrating the developed formalism. It is shown that the effective formation energy is increases with temperature, however, in this particular system it is still below the mean value of the vacancy formation energy which would correspond to the vacancy formation energy in a homogeneous model of a random alloy, such as given by the coherent potential approximation.",1512.06379v3 2016-04-01,Analysis of Feature Models Using Alloy: A Survey,"Feature Models (FMs) are a mechanism to model variability among a family of closely related software products, i.e. a software product line (SPL). Analysis of FMs using formal methods can reveal defects in the specification such as inconsistencies that cause the product line to have no valid products. A popular framework used in research for FM analysis is Alloy, a light-weight formal modeling notation equipped with an efficient model finder. Several works in the literature have proposed different strategies to encode and analyze FMs using Alloy. However, there is little discussion on the relative merits of each proposal, making it difficult to select the most suitable encoding for a specific analysis need. In this paper, we describe and compare those strategies according to various criteria such as the expressivity of the FM notation or the efficiency of the analysis. This survey is the first comparative study of research targeted towards using Alloy for FM analysis. This review aims to identify all the best practices on the use of Alloy, as a part of a framework for the automated extraction and analysis of rich FMs from natural language requirement specifications.",1604.00349v1 2016-04-11,Au-Ag-Cu nano-alloys: tailoring of permittivity,"Precious metal alloys enables new possibilities to tailor materials for specific optical functions. Here we present a systematic study of the effects of a nanoscale alloying on the permittivity of Au-Ag-Cu metals at 38 different atomic mixing ratios. The permittivity was measured and analyzed numerically by applying the Drude model. X-ray diffraction (XRD) revealed the face centered cubic lattice of the alloys. Both, optical spectra and XRD results point towards an equivalent composition-dependent electron scattering behavior. Correlation between the fundamental structural parameters of alloys and the resulting optical properties is elucidated. Plasmonic properties of the Au-Ag-Cu alloy nanoparticles were investigated by numerical simulations. Guidelines for designing plasmonic response of nano- structures and their patterns are presented from the material science perspective.",1604.02944v1 2016-05-10,Giant magnetocaloric effect near room temperature in the off-stoichiometric Mn-Co-Ge alloy,"We report a giant magnetocaloric effect near room temperature in an off-stoichiometric Mn-Co-Ge alloy, across the magnetostructural transition. The isothermal entropy change accompanying this transition has a peak value of nearly 40 J/kg-K near 297 K and a refrigerant capacity of 270 J/kg with the hot end at 302.5 K and cold end at 293.5 K. We also present an experimental protocol to avoid spurious peaks in the magnetocaloric effect across a sharp first order magnetostructural transition, not confined to Mn-Co-Ge alone, where metastability during the transition could influence the measured magnetization and thus the estimated entropy change. The estimated entropy change in the present off-stoichiometric Mn-Co-Ge alloy is possibly the highest reported value near room temperature in undoped Mn-Co-Ge alloys and underlines the potential of the alloy for technological applications in room temperature magnetic refrigeration.",1605.02902v1 2016-05-26,Phonon transport in single-layer Mo1-xWxS2 alloy embedded with WS2 nanodomains,"Two-dimensional (2-D) transition metal dichalcogenides (TMDs) have shown numerous interesting physical and chemical properties, making them promising materials for electronic, optoelectronic, and energy applications. Tuning thermal conductivity of two-dimensional (2-D) materials could expand their applicability in many of these fields. In this paper, we propose a strategy of using alloying and nanodomains to suppress the thermal conductivity of 2-D materials. To predict the thermal conductivity of 2-D alloy embedded with nanodomains, we employ the Green's function approach to assess the phonon scattering strength due to alloying and nanodomain embedding. Our first-principles-driven phonon Boltzmann transport equation calculations show that the thermal conductivity of single-layer MoS2 can be reduced to less than one-tenth of its intrinsic thermal conductivity after alloying with W and introducing nanodomains due to the strong scattering for both high- and low-frequency phonons. The strategies to further reduce the thermal conductivity are also discussed.",1605.08468v2 2016-06-16,Atomic configuration and properties of austenitic steels at finite temperature: The effect of longitudinal spin fluctuations,"High temperature atomic configurations of fcc Fe-Cr-Ni alloys with alloy composition close to austenitic steel are studied in statistical thermodynamic simulations with effective interactions obtained in ab initio calculations. The latter are done taking longitudinal spin fluctuations (LSF) into consideration within a quasiclassical phenomenological model. It is demonstrated that magnetic state affects greatly the alloy properties and in particular, it is shown that the LSF substantially modify the bonding and interatomic interactions of fcc Fe-Cr-Ni alloys even at ambient conditions. The calculated atomic short-range order (SRO) is in reasonable agreement with existing experimental data for Fe0.56}Cr0.21Ni0.23, which has strong preference for the (001) type ordering between Ni and Cr atoms. A similar ordering tendency is found for the Fe0.75Cr0.17Ni0.08 alloy composition, which approximately corresponds to the widely used 304 and 316 austenitic steel grades.",1606.05096v1 2016-07-09,Theoretical and numerical investigation of diffusive instabilities in multi-component alloys,"Mechanical properties of engineering alloys are strongly correlated to their microstructural length scale. Diffusive insta- bilities of the Mullins-Sekerka type is one of the principal mechanisms through which the scale of the microstructural features are determined during solidification. In contrast to binary systems, in multicomponent alloys with arbitrary interdiffusivities, the growth rate as well as the maximally growing wavelengths characterizing these instabilities depend on the the dynamically selected equilibrium tie-lines and the steady state growth velocity. In this study, we derive analytical expressions to characterize the dispersion behavior in isothermally solidified multicomponent (quaternary) alloys for different choices of the inter-diffusivity matrices and confirm our calculations using phase-field simulations. Thereafter, we perform controlled studies to capture and isolate the dependence of instability length scales on solute diffusivities and steady state planar front velocities, which leads to an understanding of the process of length scale selection during the onset of instability for any alloy composition with arbitrary diffusivities, comprising of both independent and coupled diffusion of solutes.",1607.02570v1 2016-09-17,A new Wang-Landau approach to obtain phase diagrams for multicomponent alloys,"We develop an approach to apply Wang-Landau algorithm to multicomponent alloys in semi-grand-canonical ensemble. Although the Wang-Landau algorithm has great advantages over conventional sampling methods, there are few applications to alloys. This is because calculating compositions in semi-grand-canonical ensemble using the Wang-Landau algorithm requires a multi-dimensional density of states in terms of total energy and compositions. However, constructing the multi-dimensional density of states is difficult. In this study, we develop a simple approach to calculate the alloy phase diagram using Wang-Landau algorithm, and show that compositions in semi-grand-canonical ensemble require just some one-dimensional densities of states. Finally, we applied the present method to Cu-Au and Pd-Rh alloys and confirmed that the present method successfully describes the phase diagram with high validity and accuracy.",1609.05292v2 2017-07-14,Alloying strategy for two-dimensional GaN optical emitters,"The recent progress in formation of two-dimensional (2D) GaN by a migration-enhanced encapsulated technique opens up new possibilities for group III-V 2D semiconductors with a band gap within the visible energy spectrum. Using first-principles calculations we explored alloying of 2D-GaN to achieve an optically active material with a tuneable band gap. The effect of isoelectronic III-V substitutional elements on the band gaps, band offsets, and spatial electron localization is studied. In addition to optoelectronic properties, the formability of alloys is evaluated using impurity formation energies. A dilute highly-mismatched solid solution 2D-GaN$_{1-x}$P$_x$ features an efficient band gap reduction in combination with a moderate energy penalty associated with incorporation of phosphorous in 2D-GaN, which is substantially lower than in the case of the bulk GaN. The group-V alloying elements also introduce significant disorder and localization at the valence band edge that facilitates direct band gap optical transitions thus implying the feasibility of using III-V alloys of 2D-GaN in light-emitting devices.",1707.04625v4 2017-07-24,Probing local lattice distortion in medium- and high-entropy alloys,"The atomic-level tunability that results from alloying multiple transition metals with d electrons in concentrated solid solution alloys (CSAs), including high-entropy alloys (HEAs), has produced remarkable properties for advanced energy applications, in particular, damage resistance in high-radiation environments. The key to understanding CSAs radiation performance is quantitatively characterizing their complex local physical and chemical environments. In this study, the local structure of a FeCoNiCrPd HEA is quantitatively analyzed with X-ray total scattering and extended X-ray absorption fine structure methods. Compared to FeCoNiCr and FeCoNiCrMn, FeCoNiCrPd with a quasi-random alloy structure has a strong local lattice distortion, which effectively pins radiation-induced defects. Distinct from a relaxation behavior in FeCoNiCr and FeCoNiCrMn, ion irradiation further enhanced the local lattice distortion in FeCoNiCrPd due to a preference for forming Pd-Pd atomic pairs.",1707.07745v1 2017-08-04,Tunable dimensional crossover and magnetocrystalline anisotropy in Fe$_2$P-based alloys,"Electronic structure calculations are used to examine the magnetic properties of Fe$_2$P-based alloys and the mechanisms through which the Curie temperature and magnetocrystalline anisotropy can be optimized for specific applications. It is found that at elevated temperatures the magnetic interaction in pure Fe$_2$P develops a pronounced two-dimensional character due to the suppression of the magnetization in one of the sublattices, but the interlayer coupling is very sensitive to band filling and structural distortions. This feature suggests a natural explanation of the observed sharp enhancement of the Curie temperature by alloying with multiple elements, such as Co, Ni, Si, and B. The magnetocrystalline anisotropy is also tunable by electron doping, reaching a maximum near the electron count of pure Fe$_2$P. These findings enable the optimization of the alloy content, suggesting co-alloying of Fe$_2$P with Co (or Ni) and Si as a strategy for maximizing the magnetocrystalline anisotropy at and above room temperature.",1708.01683v2 2017-11-07,Direct prediction of the solute softening-to-hardening transition in W-Re alloys using stochastic simulations of screw dislocation motion,"Interactions among dislocations and solute atoms are the basis of several important processes in metals plasticity. In body-centered cubic (bcc) metals and alloys, low-temperature plastic flow is controlled by screw dislocation glide, which is known to take place by the nucleation and sideward relaxation of kink pairs across two consecutive \emph{Peierls} valleys. In alloys, dislocations and solutes affect each other's kinetics via long-range stress field coupling and short-range inelastic interactions. It is known that in certain substitutional bcc alloys a transition from solute softening to solute hardening is observed at a critical concentration. In this paper, we develop a kinetic Monte Carlo model of screw dislocation glide and solute diffusion in substitutional W-Re alloys. We find that dislocation kinetics is governed by two competing mechanisms. At low solute concentrations, nucleation is enhanced by the softening of the Peierls stress, which overcomes the elastic repulsion of Re atoms on kinks. This trend is reversed at higher concentrations, resulting in a minimum in the flow stress that is concentration and temperature dependent. This minimum marks the transition from solute softening to hardening, which is found to be in reasonable agreement with experiments.",1711.02240v1 2017-11-28,Ta-Nb-Mo-W refractory high-entropy alloys: anomalous ordering behavior and its intriguing electronic origin,"From electronic-structure-based thermodynamic linear-response, we establish chemical ordering behavior in complex solid solutions versus how Gibbs' space is traversed -- applying it on prototype refractory A2 Ta-Nb-Mo-W high-entropy alloys. Near ideal stoichiometry, this alloy has anomalous, intricate chemical ordering tendencies, with long-ranged chemical interactions that produce competing short-range order (SRO) with a crossover to spinodal segregation. This atypical SRO arises from canonical band behavior that, with alloying, create features near the Fermi-surface (well-defined even with disorder) that change to simple commensurate SRO with (un)filling of these states. Our results reveal how complexity and competing electronic effects control ordering in these alloys.",1711.10591v2 2017-12-07,First-principles quantitative prediction of the lattice thermal conductivity in random semiconductor alloys: the role of force-constant disorder,"The standard theoretical understanding of the lattice thermal conductivity, $\kappa_{\ell}$, of semiconductor alloys assumes that mass disorder is the most important source of phonon scattering. In contrast, we show that the hitherto neglected contribution of force-constant (IFC) disorder is essential to accurately predict the $\kappa_{\ell}$ of those polar compounds characterized by a complex atomic-scale structure. We have developed an \emph{ab initio} method based on special quasirandom structures and Green's functions, and including the role of IFC disorder, and applied it in order to calculate the $\kappa_{\ell}$ of $\mathrm{In_{1-x}Ga_xAs}$ and $\mathrm{Si_{1-x}Ge_x}$ alloys. We show that, while for $\mathrm{Si_{1-x}Ge_x}$, phonon-alloy scattering is dominated by mass disorder, for $\mathrm{In_{1-x}Ga_xAs}$, the inclusion of IFC disorder is fundamental to accurately reproduce the experimentally observed $\kappa_{\ell}$. As the presence of a complex atomic-scale structure is common to most III-V and II-VI random semiconductor alloys, we expect our method to be suitable for a wide class of materials.",1712.02577v1 2017-12-20,Magnetic Compton profiles of disordered Fe$_{0.5}$Ni$_{0.5}$ and ordered FeNi alloys,"We study the magnetic Compton profile (MCP) of the disordered Fe$_{0.5}$Ni$_{0.5}$ and of the ordered FeNi alloys and discuss the interplay between structural disorder and electronic correlations. The Coherent Potential Approximation is employed to model the substitutional disorder within the single-site approximation, while local electronic correlations are captured with the Dynamical Mean Field Theory. Comparison with the experimental data reveals the limitation of local spin-density approximation in low momentum region, where we show that including local but dynamic correlations the experimental spectra is excellently described. We further show that using local spin-density approximation no significant difference is seen between the MCP spectra of the disordered Fe$_{0.5}$Ni$_{0.5}$ and a hypothetical, ordered FeNi alloy with a simple cubic unit cell. Only by including the electronic correlations, the spectra significantly separate, from the second Brillouin zone boundary down to zero momenta. The difference between the MCP spectra of ordered and disordered alloys is discussed also in terms of the atomic-type decompositions. Finally based on the presented calculations we predict the shape of the MCP profile for the ordered FeNi alloy along the [111] direction.",1712.07619v1 2017-12-26,Effect of Si on Fe-rich intermetallic formation and mechanical properties of heattreated Al-Cu-Mn-Fe alloys,"The effect of Si on Fe-rich intermetallics formation and mechanical properties of heat-treated squeeze cast Al-5.0Cu-0.6Mn-0.7Fe alloy was investigated. Our results show that increasing Si content promotes the formation of Al15(FeMn)3(SiCu)2 (${\alpha}$-Fe), and varying the morphology of T (Al20Cu3Mn2) where the size decreases and the amount increases. The major reason is that Si promotes heterogeneous nucleation of the intermetallics leading to finer precipitates. Si addition significantly enhances ultimate tensile strength and yield strength of the alloys. The strengthening effect is mainly owing to the dispersoid strengthening by increasing volume fraction of T phase and less harmful ${\alpha}$-Fe with a compact structure, which make the cracks more difficult to initiate and propagation during tensile test. The squeeze cast Al-5.0Cu-0.6Mn-0.7Fe alloy with 1.1% Si shows significantly improved mechanical properties than the alloy without Si addition, which has tensile strength of 386 MPa, yield strength of 280 MPa and elongation of 8.6%.",1712.09176v1 2018-01-02,Modeling solid-state dewetting of a single-crystal binary alloy thin films,"Dewetting of a binary alloy thin film is studied using a continuum many-parameter model that accounts for the surface and bulk diffusion, the bulk phase separation, the surface segregation and the particles formation. Analytical solution is found for the quasistatic equilibrium concentration of a surface-segregated atomic species. This solution is factored into the nonlinear and coupled evolution PDEs for the bulk composition and surface morphology. Stability of a planar film surface with respect to small perturbations of the shape and composition is analyzed, revealing the dependence of the particles size on major physical parameters. Computations show various scenarios of the particles formation and the redistribution of the alloy components inside the particles and on their surface. In most situations, for the alloy film composed initially of 50% A and 50% B atoms, a core-shell particles are formed, and they are located atop a wetting layer that is modestly rich in the B phase. Then the particles shell is the nanometric segregated layer of the A phase, and the core is the alloy that is modestly rich in the A phase.",1801.00764v1 2018-03-11,Characterizing solute hydrogen and hydrides in pure and alloyed titanium at the atomic scale,"Ti has a high affinity for hydrogen and is a typical hydride formers. Ti-hydride are brittle phases which probably cause premature failure of Ti-alloys. Here, we used atom probe tomography and electron microscopy to investigate the hydrogen distribution in a set of specimens of commercially pure Ti, model and commercial Ti-alloys. Although likely partly introduced during specimen preparation with the focused-ion beam, we show formation of Ti-hydrides along {\alpha} grain boundaries and {\alpha}/\b{eta} phase boundaries in commercial pure Ti and {\alpha}+\b{eta} binary model alloys. No hydrides are observed in the {\alpha} phase in alloys with Al addition or quenched-in Mo supersaturation.",1803.04007v1 2018-03-19,Tuning phase-stability and short-range order through Al-doping in (CoCrFeMn)100-xAlx high entropy alloys,"For (CoCrFeMn)$_{100-x}$Al$_{x}$ high-entropy alloys, we investigate the phase evolution with increasing Al-content (0 $\le$ x $\le$ 20 at.%). From first-principles theory, the Al-doping drives the alloy structurally from FCC to BCC separated by a narrow two-phase region (FCC+BCC), which is well supported by our experiments. We highlight the effect of Al-doping on the formation enthalpy and electronic structure of (CoCrFeMn)$_{100-x}$Al$_{x}$ alloys. As chemical short-range order (SRO) in multicomponent alloys indicates the nascent local order (and entropy changes), as well as expected low-temperature ordering behavior, we use thermodynamic linear-response within density-functional theory to predict SRO and ordering transformation and temperatures inherent in (CoCrFeMn)$_{100-x}$Al$_{x}$. The predictions agree with our present experimental findings, and other reported ones.",1803.06771v3 2018-03-30,Phase field modelling voids nucleation and growth in binary systems,"We present a comprehensive study of voids formation, nucleation and growth in a prototype model of binary alloys subjected to irradiation by using a combined approach based on phase field and rate theories. It is shown that voids formation is caused by interaction of irradiation-produced vacancies through elastic deformation of a lattice and vacancy coupling with composition field of the alloy. Phase diagrams illustrating the formation of states related to solid solution, phase decomposition, and patterning are obtained. Formation of voids from supersaturated ensemble of vacancies is accompanied by composition rearrangement of alloy components. It was found that elastic inhomogeneity leading to the formation of anisotropic precipitates in an initially prepared binary alloy results in the formation of a void super-lattice under irradiation. It was shown that voids nucleate and grow with dose according to diffusion controlled precipitation processes, where universal dynamics of voids growth is revealed. Estimations of main quantitative and statistical characteristics of voids by using material parameters relevant to most of alloys and steels give good agreement with experimental observations.",1803.11408v1 2018-05-12,Impact of corrosion on the emissivity of advanced-reactor structural alloys,"Under standard operating conditions, the emissivity of structural alloys used for various components of nuclear reactors may evolve, affecting the heat transfer of the systems. In this study, mid-infrared emissivities of several reactor structural alloys were measured before and after exposure to environments relevant to next-generation reactors. We evaluated nickel-based alloys Haynes 230 and Inconel 617 exposed to helium gas at 1000 $^{\circ}$C, nickel-based Hastelloy N and iron-based 316 stainless steel exposed to molten salts at 750-850 $^{\circ}$C, 316 stainless steel exposed to liquid sodium at 650 $^{\circ}$C, and 316 stainless steel and Haynes 230 exposed to supercritical CO2 at 650 $^{\circ}$C. Emissivity was measured via emissive and reflective techniques using a Fourier transform infrared (FTIR) spectrometer. Large increases in emissivity are observed for alloys exposed to oxidizing environments, while only minor differences were observed in other exposure conditions.",1805.04631v1 2018-06-11,Uncovering electron scattering mechanisms in NiFeCoCrMn derived concentrated solid solution and high entropy alloys,"Whilst it has long been known that disorder profoundly affects transport properties, recent measurements on a series of solid solution 3d-transition metal alloys reveal two orders of magnitude variations in the residual resistivity. Using ab-initio methods, we demonstrate that, while the carrier density of all alloys is as high as in normal metals, the electron mean-free-path can vary from ~10 {\AA} (strong scattering limit) to ~10$^3$ {\AA} (weak scattering limit). Here, we delineate the underlying electron scattering mechanisms responsible for this disparate behavior. While spin dependent site-diagonal disorder is always dominant, for alloys containing only Fe, Co, and Ni the majority spin channel experiences negligible disorder scattering, thereby providing a short circuit, while for Cr/Mn containing alloys both spin channels experience strong disorder scattering due to an electron filling effect. Unexpectedly, other scattering mechanisms (e.g. displacement scattering) are found to be relatively weak in most cases.",1806.03785v2 2021-07-19,Superconductivity in Al-Nb-Ti-V-Zr multicomponent alloy,"The superconducting high-entropy alloys (HEAs) recently attract considerable attention due to their exciting properties, such as the robustness of superconductivity against atomic disorder and extremely high-pressure. The well-studied crystal structure of superconducting HEAs is body-centered-cubic (bcc) containing Nb, Ti, and Zr atoms. The same elements are contained in Al5Nb24Ti40V5Zr26, which is a recently discovered bcc HEA and shows a gum-metal-like behavior after cold rolling. The gum metal is also an interesting system, exhibiting superelasticity and low Young's modulus. If gum metals show superconductivity and can be used as a superconducting wire, the gum-metal HEA superconductors might be the next-generation superconducting wire materials. Aiming at a fundamental assessment of as-cast Al-Nb-Ti-V-Zr multicomponent alloys including Al5Nb24Ti40V5Zr26, we have investigated the structural and superconducting properties of the alloys. All alloys investigated show the superconductivity, and the valence electron concentration dependence of the superconducting critical temperature is very close to those of typical superconducting bcc HEAs.",2107.09187v1 2017-04-10,Local segregation versus irradiation effects in high-entropy alloys: Steady-state conditions in a driven system,"We study order transitions and defect formation in a model high-entropy alloy (CuNiCoFe) under ion irradiation by means of molecular dynamics simulations. Using a hybrid Monte-Carlo/molecular dynamics scheme a model alloy is generated which is thermodynamically stabilized by configurational entropy at elevated temperatures, but partly decomposes at lower temperatures by copper precipation. Both the high-entropy and the multiphase sample are then subjected to simulated particle irradiation. The damage accumulation is analyzed and compared to an elemental Ni reference system. The results reveal that the high-entropy alloy---independent of the initial configuration---installs a certain fraction of short-range order even under particle irradiation. Moreover, the results provide evidence that defect accumulation is reduced in the high-entropy alloy. This is because the reduced mobility of point defects leads to a steady state of defect creation and annihilation. The lattice defects generated by irradiation are shown to act as sinks for Cu segregation.",1704.02812v2 2017-04-30,Comparison of dynamic mechanical properties of non-superheated and superheated A357 alloys,"The influence of superheat treatment on the microstructure and dynamic mechanical properties of A357 alloys has been investigated. The study of microstructure was performed by the optical microscope. Dynamic mechanical properties (storage modulus, loss modulus, and damping capacity) were measured by the dynamic mechanical analyzer (DMA). Microstructure showed coarser and angular eutectic Si particles with larger {\alpha}-Al dendrites in the non-superheated A357 alloy. In contrast, finer and rounded eutectic Si particles together with smaller and preferred oriented {\alpha}-Al dendrites have been observed in the superheated A357 alloy. Dynamic mechanical properties showed an increasing trend of loss modulus and damping capacity meanwhile a decreasing trend of storage modulus at elevated temperatures for superheated and non-superheated A357 alloys. The high damping capacity of superheated A357 has been ascribed to the grain boundary damping at elevated temperatures.",1705.00350v1 2018-07-17,Alloy broadening of the transition to the non-trivial topological phase of Pb_{1-x}Sn_{x}Te,"Transition between the topologically trivial and non-trivial phase of Pb_{1-x}Sn_{x}Te alloy is driven by the increasing content $x$ of Sn, or by the hydrostatic pressure for $x<0.3$. We show that a sharp border between these two topologies exists in the Virtual Crystal Approximation only. In more realistic models, the Special Quasirandom Structure method and the supercell method (with averaging over various atomic configurations), the transitions are broadened. We find a surprisingly large interval of alloy composition, $0.380 %. To validate our method, we demonstrated the capability of this method in predicting HEA solid solution phases with and without intermetallics in 30 randomly selected complex compositions, with a success rate of 77 %. The presented efficient search approach with high predictive capability can be exploited to complement computation-intense methods in providing a powerful platform for the design of high entropy alloys.",1904.08880v1 2019-04-19,Epitaxial Stabilisation of ${\bf \mathrm{Ge_{1-x}Sn_x}}$ Alloys,"The thermodynamic stability of germanium tin $\mathrm{Ge_{1-x}Sn_x}$ alloys is investigated across the composition range $0 \le x \le 1$ by applying density functional theory (DFT) together with the cluster expansion formalism (CE). It is known that GeSn alloys are immiscible and that non-equilibrium growth techniques are required to produce metastable films and nanostructures. Insight into the driving forces behind component segregation is gained by investigating the equilibrium thermodynamics of GeSn systems. The alloy free energy of mixing is computed by combining enthalpies from CE with entropy terms for configurational and vibrational degrees of freedom. Volume deformations due to the large mismatch in ionic radii are readily found to be the key driving force for immiscibility at all temperatures of relevance. This leads to a study of epitaxial stabilisation by employing latticed matched substrates to favour growth of alloys with fractional compositions of $\mathrm{x=0}$, approximately $\mathrm{x=0.5}$ and $\mathrm{x=1}$. Reduction of the free energy of mixing due to epitaxial strain in thin films is quantified for each substrate leading to indicators for growth of kinetically stable films.",1904.09147v4 2019-10-24,GaSbBi alloys and heterostructures: fabrication and properties,"Dilute bismuth (Bi) III-V alloys have recently attracted great attention, due to their properties of band-gap reduction and spin-orbit splitting. The incorporation of Bi into antimonide based III-V semiconductors is very attractive for the development of new optoelectronic devices working in the mid-infrared range (2-5 $\mu$m). However, due to its large size, Bi does not readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides is thus very challenging. This book chapter presents the most recent developments in the epitaxy and characterization of GaSbBi alloys and heterostructures.",1910.11210v1 2018-02-01,Topological Weyl semimetals in $\rm Bi$$_{1-x}$$\rm Sb$$_{x}$ alloys,"We have investigated the Weyl semimetal (WSM) phases in bismuth antimony ($\rm Bi$$_{1-x}$$\rm Sb$$_{x}$) alloys by the combination of atomic composition and arrangement. Via first principles calculations, we have found two WSM states with the Sb concentration of $x=0.5$ and $x=0.83$ with specific inversion symmetry broken elemental arrangement. The Weyl points are close to the Fermi level in both of these two WSM states. Therefore, it has a good opportunity to obtain Weyl points in Bi-Sb alloy. The WSM phase provides a reasonable explanation for the current transport study of BiSb alloy with the violation of Ohm's law [Dongwoo Shin, et al., Nature Materials 16, 1096 (2017)]. This work shows that the topological phases in Bi-Sb alloys depend on both elemental composition and their specific arrangement.",1802.00288v1 2018-08-03,"Combined ab initio and empirical model of the thermal conductivity of uranium, uranium-zirconium, and uranium-molybdenum","In this work we developed a practical and general modeling approach for thermal conductivity of metals and metal alloys that integrates ab initio and semiempirical physics-based models to maximize the strengths of both techniques. The approach supports creation of highly accurate, mechanistic, and extensible thermal conductivity modeling of alloys. The model was demonstrated on {\alpha}-U and U-rich U-Zr and U-Mo alloys, which are potential fuels for advanced nuclear reactors. The safe use of U-based fuels requires quantitative understanding of thermal transport characteristics of the fuel. The model incorporated both phonon and electron contributions, displayed good agreement with experimental data over a wide temperature range, and provided insight into the different physical factors that govern the thermal conductivity under different temperatures. This model is general enough to incorporate more complex effects like additional alloying species, defects, transmutation products, and noble gas bubbles to predict the behavior of complex metallic alloys like U-alloy fuel systems under burnup.",1808.01271v1 2018-12-10,Microscopic Geometry Rules Ordering Tendency for Multicomponent Disordered Alloys,"Short-range ordering (SRO) tendency for disordered alloys is considered as competition between chemical ordering and geometric (mainly, difference in atomic radius for constituents) effects. Especially for multicomponent (including the so-called high entropy alloys (HEAs) near equiatomic composition), it has been considered as difficult to systematically characterize the SRO tendency only by geometric effects, due mainly to the fact that (i) chemical effects typically plays significant role, (ii) near equiatomic composition, we cannnot classify which elements belong to solute or solvent, and (iii) underlying lattice for pure elements can typically differ from each other. Despite these facts, we here show that SRO tendency for seven fcc-based alloys including subsystems of Ni-based HEAs, can be well characterized by geometric effects, where corresponding atomic radius is defined based on atomic configuration with special fluctuation, measured from ideally random structure. The present findings strongly indicate the significant role of geometry in underlying lattice on SRO for multicomponent alloys.",1812.03690v1 2019-02-19,Mixed structural face-centered cubic and body-centered cubic orders in near stoichiometric Fe2MnGa alloys,"Magnetic and transport properties of near-stoichiometric metastable FexMnyGaz alloys (46