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 (Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within $\approx$2$^\circ$. 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

Direct experimental evidence of tunable charge transfer at the LaNiO3/CaMnO3LaNiO_{3}/CaMnO_{3} 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 $LaNiO_{3}$ on the electronic and magnetic states at the $LaNiO_{3}/CaMnO_{3}$ 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 $LaNiO_{3}$ thickness (6 u.c.) due to the leakage of itinerant Ni 3d $e_{g}$ electrons into the interfacial $CaMnO_{3}$ layer. Conversely, in an insulating superlattice with a below-critical $LaNiO_{3}$ thickness of 2 u.c., a homogeneous effective valence state of Mn is observed throughout the $CaMnO_{3}$ 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 $LaNiO_{3}/CaMnO_{3}$ interface and, thus, has far-reaching consequences on the future strategies for the design of next-generation spintronic devices

Coherent transfer of spin angular momentum by evanescent spin waves within antiferromagnetic NiO

This is the final version. Available from the publisher via the DOI in this record.Insulating antiferromagnets have recently emerged as efficient and robust conductors of spin current. Element-specific and phase-resolved x-ray ferromagnetic resonance has been used to probe the injection and transmission of ac spin current through thin epitaxial NiO(001) layers. The spin current is found to be mediated by coherent evanescent spin waves of GHz frequency, rather than propagating magnons of THz frequency, paving the way towards coherent control of the phase and amplitude of spin currents within an antiferromagnetic insulator at room temperature.Engineering and Physical Science Research Council (EPSRC

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

Coherent ac spin current transmission across an antiferromagnetic CoO insulator

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: Data are available from the corresponding author upon reasonable request.The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe75Co25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO.US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering DivisionNational Science Foundation (NSF)National Research Foundation of KoreaEngineering and Physical Sciences Research Council (EPSRC)National Key Research and Development Program of CHIN

Element- and Time-Resolved Measurements of Spin Dynamics Using X-ray Detected Ferromagnetic Resonance

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this recordThe technique of x-ray detected ferromagnetic resonance (XFMR) represents an indispensable new tool in the investigation of spin current effects in complex heterostructures, as it enables the observation of magnetization and spin dynamics with element-, site-, and valence state-specificity. Here we give an overview of the development of XFMR and characterize different approaches to measure spin dynamics using synchrotron radiation. We provide a detailed description of the working principle of the technique and give an overview of recent work carried out at beamline 4.0.2 of the Advanced Light Source and beamline I10 of the Diamond Light Source using XFMR. Results from our latest publications demonstrate the capabilities and sensitivity of the technique. Element- and phase-resolution provide intriguing insights into the mechanisms of spin current propagation in multilayers, while the high sensitivity of XFMR allows for detection of even miniscule signals. Most recently, the utilization of linearly polarized x-rays for XFMR and the detection of XFMR by means of x-ray diffraction rather than x-ray absorption demonstrate two new capabilities in the investigation of spin dynamics.Engineering and Physical Sciences Research Council (EPSRC)US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering DivisionNational Research Foundation of Kore

Observation of room-temperature polar skyrmions

peer reviewe

Optically and microwave induced magnetization precession in [Co/Pt]/NiFe exchange springs

This is the final version. Available from the American Chemical Society via the DOI in this recordMicrowave and heat-assisted magnetic recordings are two competing technologies that have greatly increased the capacity of hard disk drives. The efficiency of the magnetic recording process can be further improved by employing non-collinear spin structures that combine perpendicular and in-plane magnetic anisotropy. Here, we investigate both microwave and optically excited magnetization dynamics in [Co/Pt]/NiFe exchange spring samples. The resulting canted magnetization within the nanoscale [Co/Pt]/NiFe interfacial region allows for optically stimulated magnetization precession to be observed for an extended magnetic field and frequency range. The results can be explained by formation of an imprinted domain structure, which locks the magnetization orientation and makes the structures more robust against external perturbations. Tuning the canted interfacial domain structure may provide greater control of optically excited magnetization reversal and optically generated spin currents, which are of paramount importance for future ultrafast magnetic recording and spintronic applications.Engineering and Physical Sciences Research Council (EPSRC

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