publicationDate,title,abstract,id
2022-01-12,Light and microwave driven spin pumping across FeGaB-BiSb interface,"3-D topological insulators (TI) with large spin Hall conductivity have
emerged as potential candidates for spintronic applications. Here, we report
spin to charge conversion in bilayers of amorphous ferromagnet (FM)
Fe_{78}Ga_{13}B_{9} (FeGaB) and 3-D TI Bi_{85}Sb_{15} (BiSb) activated by two
complementary techniques: spin pumping and ultrafast spin-current injection. DC
magnetization measurements establish the soft magnetic character of FeGaB
films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband
ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing
magnetization and large value of spin mixing conductance (5.03 x 10^{19}
m^{-2}) as the spin angular momentum leaks into the TI layer. Magnetic field
controlled bipolar dc voltage generated across the TI layer by inverse spin
Hall effect is analyzed to extract the values of spin Hall angle and spin
diffusion length of BiSb. The spin pumping parameters derived from the
measurements of the femtosecond light-pulse-induced terahertz emission are
consistent with the result of FMR. Kubo-Bastin formula and tight-binding model
calculations shed light on the thickness-dependent spin-Hall conductivity of
the TI films, with predictions that are in remarkable agreement with the
experimental data. Our results suggest that room temperature deposited
amorphous and polycrystalline heterostructures provide a promising platform for
creating novel spin orbit torque devices.",2201.04686v1
2024-03-21,Picotesla-sensitivity microcavity optomechanical magnetometry,"Cavity optomechanical systems have enabled precision sensing of magnetic
fields, by leveraging the optical resonance-enhanced readout and mechanical
resonance-enhanced response. Previous studies have successfully achieved
scalable and reproducible microcavity optomechanical magnetometry (MCOM) by
incorporating Terfenol-D thin films into high-quality ($Q$) factor whispering
gallery mode (WGM) microcavities. However, the sensitivity was limited to 585
pT/Hz$^{1/2}$, over 20 times inferior to those using Terfenol-D particles. In
this work, we propose and demonstrate a high-sensitivity and scalable MCOM
approach by sputtering a FeGaB thin film onto a high-$Q$ SiO$_2$ WGM microdisk.
Theoretical studies are conducted to explore the magnetic actuation constant
and noise-limited sensitivity by varying the parameters of the FeGaB film and
SiO$_2$ microdisk. Multiple magnetometers with different radii are fabricated
and characterized. By utilizing a microdisk with a radius of 355 $\mu$m and a
thickness of 1 $\mu$m, along with a FeGaB film with a radius of 330 $\mu$m and
a thickness of 1.3 $\mu$m, we have achieved a remarkable peak sensitivity of
1.68 pT/Hz$^{1/2}$ at 9.52 MHz. This represents a significant improvement of
over two orders of magnitude compared with previous studies employing sputtered
Terfenol-D film. Notably, the magnetometer operates without a bias magnetic
field, thanks to the remarkable soft magnetic properties of the FeGaB film.
Furthermore, as a proof-of-concept, we have demonstrated the real-time
measurement of a pulsed magnetic field simulating the corona current in a
high-voltage transmission line using our developed magnetometer. These
high-sensitivity magnetometers hold great potential for various applications,
such as magnetic induction tomography and corona current monitoring.",2403.14301v1
2015-08-28,Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching,"Electric-field modulation of magnetism in strain-mediated multiferroic
heterostructures is considered a promising scheme for enabling memory and
magnetic microwave devices with ultralow power consumption. However, it is not
well understood how electric-field-induced strain influences magnetic
relaxation, an important physical process for device applications. Here we
investigate resonant magnetization dynamics in ferromagnet/ferrolectric
multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct
strain states provided by electric-field-induced ferroelectric phase
transition. The strain not only modifies magnetic anisotropy but also magnetic
relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic
Gilbert damping by electric field, which is attributed to strain-induced tuning
of spin-orbit coupling. By contrast, a small but measurable change in extrinsic
linewidth broadening is attributed to inhomogeneous ferroelastic domain
switching during the phase transition of the PMN-PT substrate.",1508.07290v2
2022-01-11,Resonant Precession of Magnetization and Precession -- Induced DC voltages in FeGaB Thin Films,"Measurements of frequency dependent ferromagnetic resonance (FMR) and spin
pumping driven dc voltage (V_{dc}) are reported for amorphous films of
Fe_{78}Ga_{13}B_{9} (FeGaB) alloy to address the phenomenon of self-induced
inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets. The
V_{dc} signal, which is antisymmetric on field reversal, comprises of symmetric
and asymmetric Lorentzians centered around the resonance field. Dominant role
of thin film size effects is seen in setting the magnitude of static
magnetization, V_{dc} and dynamics of magnetization precession in thinner films
(\leq 8 nm). The film thickness dependence of magnetization parameters
indicates the presence of a magnetically disordered region at the
film-substrate interface, which may promote preferential flow of spins
generated by the precessing magnetization towards the substrate. However, the
V_{dc} signal also draws contributions from rectification effects of a \approx
0.4 \% anisotropic magnetoresistance and a large (\approx 54 n\Omega.m)
anomalous Hall resistivity (AHR) of these films which ride over the effect of
spin-orbit coupling driven spin-to-charge conversion near the film-substrate
interface. We have addressed these data in the framework of the existing
theories of electrodynamics of a ferromagnetic film subjected to
radio-frequency field in a coplanar waveguide geometry. Our estimation of the
self-induced ISHE for the sample with 54 n\Omega.m AHR shows that it may
contribute significantly (\approx 90\%) to the measured symmetric voltage. This
study is expected to be very useful for fully understanding the spin pumping
induced dc voltages in metallic ferromagnets with disordered interfaces and
large anomalous Hall effect.",2201.03739v1
2014-11-22,Quantification of the spin-Hall anti-damping torque with a resonance spectrometer,"We present a simple technique using a cavity-based resonance spectrometer to
quantify the anti-damping torque due to the spin Hall effect. Modification of
ferromagnetic resonance is observed as a function of small DC current in
sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and
strong spin-Hall metal Ta. From the detected current-induced linewidth change,
we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic
layer thickness. Our results demonstrate that a sensitive resonance
spectrometer can be a general tool to investigate spin Hall effects in various
material systems, even those with vanishingly low conductivity and
magnetoresistance.",1411.6166v1
2021-12-10,Enhanced Planar Antenna Efficiency Through Magnetic Thin-Films,"This work proposes to use magnetic material as the substrate of planar
antennas to overcome the platform effect caused by the conducting ground plane.
The upper bound of the radiation efficiency of an electric-current-driven
low-profile antenna is theoretically derived, which is inversely proportional
to the Gilbert damping factor of the magnetic material. Meanwhile, the
improvement of radiation due to the use of magnetic material is demonstrated by
a three-dimensional (3D) multiphysics and multiscale time-domain model. The
simulation results match the theoretical derivation, showing 25% radiation
efficiency from a planar antenna backed by a FeGaB thin film with 2.56 um
thickness. Furthermore, for conductive ferromagnetic materials, it is shown
that the eddy current loss can be well suppressed by laminating the thin film
into multiple layers. The radiation efficiency of the modeled antenna with a
conductive ferromagnetic substrate is improved from 2.2% to 11.8% by dividing
the substrate into 10 layers, with a ferromagnetic material fill factor of 93%.",2201.04932v1