31 research outputs found
Direct experimental evidence of tunable charge transfer at the ferromagnetic interface
Interfacial charge transfer in oxide heterostructures gives rise to a rich
variety of electronic and magnetic phenomena. Designing heterostructures where
one of the thin-film components exhibits a metal-insulator transition opens a
promising avenue for controlling such phenomena both statically and
dynamically. In this letter, we utilize a combination of depth-resolved soft
X-ray standing-wave and hard X-ray photoelectron spectroscopies in conjunction
with polarization-dependent X-ray absorption spectroscopy to investigate the
effects of the metal-insulator transition in on the electronic and
magnetic states at the interface. We report on a direct
observation of the reduced effective valence state of the interfacial Mn
cations in the metallic superlattice with an above-critical
thickness (6 u.c.) due to the leakage of itinerant Ni 3d electrons into
the interfacial layer. Conversely, in an insulating superlattice
with a below-critical thickness of 2 u.c., a homogeneous effective
valence state of Mn is observed throughout the layers due to the
blockage of charge transfer across the interface. The ability to switch and
tune interfacial charge transfer enables precise control of the emergent
ferromagnetic state at the interface and, thus, has
far-reaching consequences on the future strategies for the design of
next-generation spintronic devices
Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide
Many technologically useful magnetic oxides are ferrimagnetic insulators,
which consist of chemically distinct cations. Here, we examine the spin
dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite
(NiZnAlFeO) under continuous microwave
excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance
to separately probe Fe and Ni cations on different sublattice
sites. Our results show that the precessing cation moments retain a rigid,
collinear configuration to within 2. Moreover, the effective
spin relaxation is identical to within 10% for all magnetic cations in the
ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in
resonantly driven ferrimagnetic oxides, where the magnetic moments from
different cations precess as a coherent, collective magnetization
Dependence of spin pumping and spin transfer torque upon Ni81Fe19 thickness in Ta/Ag/Ni81Fe19/Ag/Co2MnGe/Ag/Ta spin-valve structures
This is the final version of the article. Available from American Physical Society via the DOI in this record.Spin pumping has been studied within Ta / Ag /
Ni
81
Fe
19
(0–5 nm) / Ag (6 nm) /
Co
2
MnGe
(5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of
Ni
81
Fe
19
sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the
Co
2
MnGe
source layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.The authors gratefully acknowledge the support of EPSRC Grant No. EP/J018767/1, and the award of the Exeter-Brown Scholarship in High Frequency Spintronics to C.J.D
Observation of room-temperature polar skyrmions
peer reviewe
Manipulating chiral-spin transport with ferroelectric polarization
A collective excitation of the spin structure in a magnetic insulator can
transmit spin-angular momentum with negligible dissipation. This quantum of a
spin wave, introduced more than nine decades ago, has always been manipulated
through magnetic dipoles, (i.e., timereversal symmetry). Here, we report the
experimental observation of chiral-spin transport in multiferroic BiFeO3, where
the spin transport is controlled by reversing the ferroelectric polarization
(i.e., spatial inversion symmetry). The ferroelectrically controlled magnons
produce an unprecedented ratio of up to 18% rectification at room temperature.
The spin torque that the magnons in BiFeO3 carry can be used to efficiently
switch the magnetization of adja-cent magnets, with a spin-torque efficiency
being comparable to the spin Hall effect in heavy metals. Utilizing such a
controllable magnon generation and transmission in BiFeO3, an alloxide,
energy-scalable logic is demonstrated composed of spin-orbit injection,
detection, and magnetoelectric control. This observation opens a new chapter of
multiferroic magnons and paves an alternative pathway towards low-dissipation
nanoelectronics
The role of GRK6 in animal models of Parkinson's Disease and L-DOPA treatment
G protein-coupled Receptor Kinase 6 (GRK6) belongs to a family of kinases that phosphorylate GPCRs. GRK6 levels were found to be altered in Parkinson's Disease (PD) and D2 dopamine receptors are supersensitive in mice lacking GRK6 (GRK6-KO mice). To understand how GRK6 modulates the behavioral manifestations of dopamine deficiency and responses to L-DOPA, we used three approaches to model PD in GRK6-KO mice: 1) the cataleptic response to haloperidol; 2) introducing GRK6 mutation to an acute model of absolute dopamine deficiency, DDD mice; 3) hemiparkinsonian 6-OHDA model. Furthermore, dopamine-related striatal signaling was analyzed by assessing the phosphorylation of AKT/GSK3β and ERK1/2. GRK6 deficiency reduced cataleptic behavior, potentiated the acute effect of L-DOPA in DDD mice, reduced rotational behavior in hemi-parkinsonian mice, and reduced abnormal involuntary movements induced by chronic L-DOPA. These data indicate that approaches to regulate GRK6 activity could be useful in modulating both therapeutic and side-effects of L-DOPA
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Strain-Induced Orbital Contributions to Oxygen Electrocatalysis in Transition-Metal Perovskites
Epitaxial strain has been shown to produce dramatic changes to the orbital structure in transition metal perovskite oxides and, in turn, the rate of oxygen electrocatalysis therein. Here, epitaxial strain is used to investigate the relationship between surface electronic structure and oxygen electrocatalysis in prototypical fuel cell cathode systems. Combining high-temperature electrical-conductivity-relaxation studies and synchrotron-based X-ray absorption spectroscopy studies of La0.5Sr0.5CoO3 and La0.8Sr0.2Co0.2Fe0.8O3 thin films under varying degrees of epitaxial strain reveals a strong correlation between orbital structure and catalysis rates. In both systems, films under biaxial tensile strain simultaneously exhibit the fastest reaction kinetics and lowest electron occupation in the dz2 orbitals. These results are discussed in the context of broader chemical trends and electronic descriptors are proposed for oxygen electrocatalysis in transition metal perovskite oxides