arXiv subjects

Shilei Ding

Publications and source records attributed to Shilei Ding.

At least 19 recordsLinked to original sources

arXiv2026

High-mobility inertial domain walls driven by spin-transfer torque in a ferrimagnetic spinel oxide

Efficient electrical manipulation of domain walls is key to developing magnetic devices with fast switching capabilities and low energy consumption. Here we demonstrate Bloch-type domain wall velocities exceeding 1 km s$^{-1}$ in the single-layer ferrimagnetic spinel oxide NiCo$_2$O$_4$ induced by spin-transfer torque at a current density of $2 \times 10^{11}$ A m$^{-2}$. This exceptional domain wall mobility is attributed to the combination of giant nonadiabatic spin-transfer torque, low magnetization, and high spin polarization. Additionally, we report a pronounced domain wall inertia effect in this ferrimagnet due to the large nonadiabaticity of the torque. The characteristic time for domain wall acceleration and deceleration is $\sim 1$ ns, shorter than that reported for typical ferromagnets. Our findings highlight the potential of spinel oxides as a promising platform for engineering high-performance domain wall devices that take advantage of ultrafast ferrimagnetic dynamics.

cond-mat.mes-hall↗

arXiv2026

Generating unconventional spin-orbit torques with patterned phase gradients in tungsten thin films

A key aim in spintronics is to achieve current-induced magnetization switching via spin-orbit torques without external magnetic fields. For this, the focus of recent work has been on introducing controlled lateral gradients across ferromagnet/heavy-metal devices, giving variations in thickness, composition, or interface quality. However, the small gradients achievable with common growth techniques limit both the impact of this approach and understanding of the underlying physical mechanisms. Here, spin-orbit torques are patterned on a mesoscopic length scale in tungsten thin films using direct-write laser annealing. Through transmission electron microscopy, resistivity, and second harmonic measurements, the continuous transformation of the crystalline phase of W films from the highly spin-orbit coupled, high resistivity $\beta$ phase to the minimally spin-orbit coupled, low resistivity $\alpha$ phase is tracked with increasing laser fluence. Gradients with different steepness are patterned in the tungsten phase to create spin-orbit torque channels and, when interfaced with CoFeB, tungsten wires with a sufficiently strong gradient can switch the magnetization without an applied magnetic field. Therefore, exploiting the unique microstructure of mixed-phase W allows precise control of the local electronic current density and direction, as well as local spin-orbit torque efficiency, providing a new avenue for the design of efficient spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Unidirectional magnetoresistance driven by nonequilibrium antiferromagnetic magnons

Magnetoresistive effects are typically symmetric under magnetization reversal. However, nonlinear spin transport can give rise to unidirectional magnetoresistance in systems with strong spin-orbit interaction and broken inversion symmetry. Here, we demonstrate that the nonequilibrium magnon accumulation characterized by a finite magnon chemical potential can lead to a large and robust magnonic unidirectional spin Hall magnetoresistance (USMR) in the weakly coupled van der Waals antiferromagnet CrPS4 in contact with Pt. Unlike conventional magnonic USMR driven by magnetization fluctuations, this effect persists under strong magnetic fields and low temperatures, with a pronounced peak near the spin-flip transition. The magnitude of magnonic USMR in CrPS4/Pt exceeds that of YIG/Pt by more than two orders of magnitude and surpasses the electrical USMR in metallic Ta/Co bilayers by a factor of two. The observed field and temperature dependence indicates that spin transport is dominated by magnon chemical potential gradients rather than thermal- or fluctuation-driven magnon generation. These findings establish a new mechanism for nonlinear magnetoresistance in antiferromagnetic van der Waals heterostructures and open a route to magnon-based antiferromagnetic spintronic functionalities in two-terminal device geometries.

cond-mat.mtrl-sci↗

arXiv2025

Acoustic orbital Hall effect and orbital pumping in light-metal-ferromagnet bilayers

Orbital currents provide a new degree of freedom for controlling magnetism, yet their interaction with lattice dynamics remains largely unexplored. Here we report a systematic investigation of the acoustic orbital Hall effect in light metals such as Ti and Cr, where surface acoustic waves generate orbital currents through phonon-orbital coupling. The acoustic orbital current in Ti exhibits higher efficiency and longer diffusion length compared to the acoustic spin current in Pt. The sign and magnitude of the rectified acoustic voltages in nonmagnetic (Ti, Cr)/ferromagnetic (Ni, Co, Fe$_x$Co$_{1-x}$) bilayers are determined by the product of orbital-to-spin conversion and magnetoelastic coupling efficiencies of the ferromagnet. Additionally, we find evidence for acoustic orbital pumping, whereby the excitation of ferromagnetic resonance by surface acoustic waves injects an orbital current from the ferromagnet into the nonmagnet. These results establish lattice dynamics as an efficient driver of orbital transport, opening opportunities for low-dissipation orbitronic devices that harness and sense phonons.

cond-mat.mes-hall↗

arXiv2025

Orbital Pumping in Ferrimagnetic Insulators

We report the detection of pure orbital currents generated by both coherent and thermal magnons in the magnetic insulator Bi-doped yttrium iron garnet (BiYIG). The pumping of orbital and spin currents is jointly investigated in nano-devices made of naturally oxidized Cu, pure Cu, Pt, and Cr. The absence of charge conduction in BiYIG and the negligible spin-to-charge conversion of oxidized Cu allows us to disambiguate the orbital current contribution. Comparative measurements on YIG and BiYIG show that the origin of the orbital pumping in BiYIG/oxidized Cu is the dynamics of the orbital magnetization in the magnetic insulator. In Cr, the pumping signal is dominated by the negative spin Hall effect rather than the positive orbital Hall effect, indicating that orbital currents represent a minority of the total angular momentum current pumped from the magnetic insulator. Our results also evidence that improving the interfacial transparency significantly enhances pumping efficiencies not only for spin, but also for orbital currents.

cond-mat.mes-hall↗

arXiv2025

Reconfigurable Room Temperature Exchange Bias through N\'eel Order Switching in van der Waals Heterostructures

Exchange bias effect plays a crucial role in modern magnetic memory technology. Recently, van der Waals magnetic materials have emerged and shown potential in spintronic devices at atomic scale. Owing to their tunable physical properties and the flexibility in fabrication, the van der Waals heterostructures offer more possibilities for investigating potential mechanisms of the exchange bias effect. However, due to low magnetic ordering temperatures for most van der Waals magnets, to establish exchange bias in van der Waals antiferromagnet/ferromagnet heterostructures at room temperature is challenging. In this study, we fabricate (Fe$_{0.56}$Co$_{0.44}$)$_{5}$GeTe$_{2}$(FCGT)/Fe$_{3}$GaTe$_{2}$(FGaT) heterostructures with magnetic ordering temperatures of each component well above room temperature to achieve a room temperature exchange bias effect. It is found that the sign and magnitude of the exchange bias field can be efficiently controlled by manipulating the N\'eel order of FCGT with magnetic field. The manipulation of N\'eel order shows significant magnetic field dependence. A strong pre-set field induces a switch in the N\'eel order of FCGT, which aligns the interfacial magnetization at the FCGT/FGaT interface, leading to robust exchange bias, as revealed by both transport measurements and macro-spin model calculations. Our findings demonstrate the intrinsic manipulation and switchable of room-temperature exchange bias in all-van der Waals heterostructures and further promote the development of novel two-dimensional spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Tailoring spin reorientation and magnetic interaction for room-temperature spintronics in Tb-Doped SmFeO3 single crystal

Selective doping with different R-site ions in rare-earth perovskite RFeO3 compounds offers an effective way to achieve atomic-scale tuning of the complex exchange interactions. In this study, the spin reorientation temperature of Tb-doped SmFeO3 (Sm0.7Tb0.3FeO3) single crystal is lowered to approximately 350 K, making it more suitable for room-temperature applications. Notably, the magnetic compensation point is absent at low temperatures, and both R3+ and Fe3+ ion moments can be fully saturated under high magnetic fields, suggesting that Tb3+ doping drives the R3+ and Fe3+ sublattices toward ferromagnetic coupling. Moreover, the hysteresis loop along the a-axis transitions from a double triangle shape below the spin reorientation temperature to a rectangular shape above the spin reorientation temperature, and the nucleation field exhibits a strong dependence on both the measurement temperature and the maximum applied magnetic field. Above results can be explained by a modified two-domain model with mean field correction. The results of magnetic domain measurements indicate that the emergence of the double-triangular hysteresis loop is jointly determined by domain wall motion and the nonlinear response of the parasitic magnetic moment along the a-axis. These findings provide valuable insights and new materials for advancing the use of RFeO3 compounds in spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic Orbital Hall Effect in Altermagnet RuO$_2$

Orbital angular momentum provides an alternative channel for current-induced magnetization switching beyond conventional spin--orbit coupling. While orbital Hall effects have been observed in several nonmagnetic materials, their manifestation in symmetry-compensated magnetic systems remains unexplored. Here, we report experimental evidence for a magnetic orbital Hall effect in RuO$_2$. In RuO$_2$(101)/Pt/Co heterostructures, we observe a pronounced unconventional torque characterized by a large out-of-plane component, strong crystalline anisotropy, and deterministic field-free switching of a perpendicular ferromagnet over a wide range of RuO$_2$ thicknesses. The torque exhibits a non-monotonic dependence on Pt thickness, reaching a maximum at 1.5~nm, and displays a long-range RuO$_2$ thickness ($t_{\mathrm{RuO}_2}$) dependence that saturates for $t_{\mathrm{RuO}_2}>100~\mathrm{nm}$. These features cannot be reconciled with conventional spin-current mechanisms. Rather, they indicate a magnetic orbital Hall effect in RuO$_2$ that could originate from exchange-induced momentum-dependent band splitting and its interplay with spin--orbit and crystal-field coupling, with the generated orbital current converted into torque in Pt. Our findings establish altermagnets as intrinsic sources of orbital currents and extend orbitronics to symmetry-compensated magnetic systems.

cond-mat.mes-hall↗

arXiv2024

Spin Seebeck in the weak exchange coupled van der Waals antiferromagnet

Spin Seebeck effect (SSE) refers to the creation of spin currents due to a temperature gradient in the magnetic materials or across magnet-normal metal interfaces, which can be electrically detected through the inverse spin Hall effect (ISHE) when in contact with heavy metals. It offers fundamental insights into the magnetic properties of materials, including the magnetic phase transition, static magnetic order, and magnon excitations. However, the SSE in van der Waals antiferromagnet is still elusive, especially across the spin-flip transition. Here, we demonstrate the SSE in the weak exchange coupled van der Waals antiferromagnet CrPS$_4$. The SSE increases as the magnetic field increases before the spin-flip transition due to the enhancement of the thermal spin current as a function of the applied field. A peak of SSE is observed at the spin-flip field, which is related to the magnon mode edges across the spin-flip field. Our results extend SSE research to van der Waals antiferromagnets and demonstrate an enhancement of SSE at the spin-flip transition.

physics.app-ph↗

arXiv2024

Mitigation of Gilbert Damping in the CoFe/CuOx Orbital Torque System

Charge-spin interconversion processes underpin the generation of spin-orbit torques in magnetic/nonmagnetic bilayers. However, efficient sources of spin currents such as 5d metals are also efficient spin sinks, resulting in a large increase of magnetic damping. Here we show that a partially-oxidized 3d metal can generate a strong orbital torque without a significant increase in damping. Measurements of the torque efficiency {\xi} and Gilbert damping {\alpha} in CoFe/CuOx and CoFe/Pt indicate that {\xi} is comparable. The increase in damping relative to a single CoFe layer is {\Delta}{\alpha}<0.002 in CoFe/CuOx and {\Delta}{\alpha} ~ 0.005 - 0.02 in CoFe/Pt, depending on CoFe thickness. We ascribe the nonreciprocal relationship between {\Delta}{\alpha} and {\xi} in CoFe/CuOx to the small orbital-to-spin current ratio generated by magnetic resonance in CoFe and the lack of an efficient spin sink in CuOx. Our findings provide new perspectives on the efficient excitation of magnetization dynamics via the orbital torque.

cond-mat.mtrl-sci↗

arXiv2024

Orbital Torque in Rare-Earth Transition-Metal Ferrimagnets

Orbital currents have recently emerged as a promising tool to achieve electrical control of the magnetization in thin-film ferromagnets. Efficient orbital-to-spin conversion is required in order to torque the magnetization. Here we show that the injection of an orbital current in a ferrimagnetic GdyCo100-y alloy generates strong orbital torques whose sign and magnitude can be tuned by changing the Gd content and temperature. The effective spin-orbital Hall angle reaches up to -0.25 in a GdyCo100-y/CuOx bilayer compared to +0.03 in Co/CuOx and +0.13 in GdyCo100-y/Pt. This behavior is attributed to the local orbital-to-spin conversion taking place at the Gd sites, which is about five times stronger and of the opposite sign relative to Co. Furthermore, we observe a manyfold increase in the net orbital torque at low temperature, which we attribute to the improved conversion efficiency following the magnetic ordering of the Gd and Co sublattices.

cond-mat.mtrl-sci↗

arXiv2022

Unidirectional orbital magnetoresistance in light metal/ferromagnet bilayers

We report the observation of a unidirectional magnetoresistance (UMR) that originates from the nonequilibrium orbital momentum induced by an electric current in a naturally oxidized Cu/Co bilayer. The orbital-UMR scales with the torque efficiency due to the orbital Rashba-Edelstein effect upon changing the Co thickness and temperature, reflecting their common origin. We attribute the UMR to orbital-dependent electron scattering and orbital-to-spin conversion in the ferromagnetic layer. In contrast to the spin-current induced UMR, the magnon contribution to the orbital-UMR is absent in thin Co layers, which we ascribe to the lack of coupling between low energy magnons and orbital current. The magnon contribution to the UMR emerges in Co layers thicker than about 5 nm, which is comparable to the orbital-to-spin conversion length. Our results provide insight into orbital-to-spin momentum transfer processes relevant for the optimization of spintronic devices based on light metals and orbital transport.

cond-mat.mtrl-sci↗

arXiv2021

Electrical detection of the spin-flop and room-temperature magnetic ordering in van der Waals CrPS$_{4}$/(Pt, Pd) heterostructures

We study magneto-transport in heterostructures composed of the van der Waals antiferromagnet CrPS$_{4}$ and the heavy metals Pt and Pd. The transverse resistance (R$_{xy}$) signal reveals the spin-flop transition of CrPS$_{4}$ and a strongly enhanced magnetic ordering temperature (>300 K), which might originate from a strong spin-orbit coupling at the interface. While CrPS$_{4}$/Pt devices allow for easy detection of the spin-flop transition, CrPS$_{4}$/Pd devices show a more substantial enhancement in magnetic ordering temperature and exhibit a topological Hall effect signal, possibly related to chiral spin structures at the interface. The longitudinal magnetoresistance (R$_{xx}$) results from a combination of spin-Hall magnetoresistance and the negative magnetoresistance that can be explained by a field-induced change of the electronic band structure of CrPS$_{4}$.

physics.app-ph↗

arXiv2021

Observation of the Orbital Rashba-Edelstein Magnetoresistance

We report the observation of magnetoresistance (MR) originating from the orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu (Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance (SMR). Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional SMR which requires heavy elements. By varying the thickness of the Cu* layer, we confirm that the interface is responsible for the MR, suggesting that the orbital Rashba-Edelstein effect is responsible for the generation of the OAM. Through Py thickness-dependence studies, we find that the effective values for the spin diffusion and spin dephasing lengths of Py are significantly larger than the values measured in Py / Pt bilayers, approximately by the factor of 2 and 4, respectively. This implies that another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py / Cu* structures originated in a sizeable transport of OAM. Our findings not only unambiguously demonstrate the current-induced torque without using any heavy element via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.

cond-mat.mtrl-sci↗

arXiv2021

Magnetic coupling in Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ heterostructures

Ferrimagnetic Y$_3$Fe$_5$O$_{12}$ (YIG) is the prototypical material for studying magnonic properties due to its exceptionally low damping. By substituting the yttrium with other rare earth elements that have a net magnetic moment, we can introduce an additional spin degree of freedom. Here, we study the magnetic coupling in epitaxial Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ (YIG/GIG) heterostructures grown by pulsed laser deposition. From bulk sensitive magnetometry and surface sensitive spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) measurements, we determine the alignment of the heterostructure magnetization through temperature and external magnetic field. The ferromagnetic coupling between the Fe sublattices of YIG and GIG dominates the overall behavior of the heterostructures. Due to the temperature dependent gadolinium moment, a magnetic compensation point of the total bilayer system can be identified. This compensation point shifts to lower temperatures with increasing thickness of YIG due the parallel alignment of the iron moments. We show that we can control the magnetic properties of the heterostructures by tuning the thickness of the individual layers, opening up a large playground for magnonic devices based on coupled magnetic insulators. These devices could potentially control the magnon transport analogously to electron transport in giant magnetoresistive devices.

cond-mat.mtrl-sci↗

arXiv2021

Identification of Néel vector orientation in antiferromagnetic domains switched by currents in NiO/Pt thin films

Understanding the electrical manipulation of antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequency. Focusing on collinear insulating antiferromagnetic NiO/Pt thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the Néel vector direction changes. We demonstrate electrical switching between different T-domains by current pulses, finding that the Néel vector orientation in these domains is along $[\pm5\ \pm5\ 19]$, different compared to the bulk $<11\bar{2}>$ directions. The final state of the Néel vector $\textbf{n}$ switching after current pulses $\textbf{j}$ along the $[1\ \pm1\ 0]$ directions is $\textbf{n}\parallel \textbf{j}$. By comparing the observed Néel vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as $b_{0}+2b_{1}=3*10^7 J\ m^{-3}$ . This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.

cond-mat.mtrl-sci↗

arXiv2020

Identifying the origin of the non-monotonic thickness dependence of spin-orbit torques and interfacial Dzyaloshinskii-Moriya interaction in a ferrimagnetic insulator heterostructure

Electrical manipulation of magnetism via spin-orbit torques (SOTs) promises efficient spintronic devices. In systems comprising magnetic insulators and heavy metals, SOTs have started to be investigated only recently, especially in systems with interfacial Dzyaloshinskii-Moriya interaction (iDMI). Here, we quantitatively study the SOT efficiency and iDMI in a series of gadolinium gallium garnet (GGG) / thulium iron garnet (TmIG) / platinum (Pt) heterostructures with varying TmIG and Pt thicknesses. We find that the non-monotonic SOT efficiency as a function of the magnetic layer thickness is not consistent with the 1/thickness dependence expected from a simple interfacial SOT mechanism. Moreover, considering the insulating nature of TmIG, our results cannot be explained by the SOT mechanism established for metallic magnets where the transverse charge spin current can inject and dephase in the magnetic layers. Rather we can explain this non-monotonic behavior by a model based on the interfacial spin mixing conductance that is affected by the thickness-dependent exchange splitting energy by determining the phase difference of the reflected spin-up and spin-down electrons at the TmIG / Pt interface. By studying the Pt thickness dependence, we find that the effective DMI for GGG / TmIG / Pt does not depend on the Pt thickness, which indicates that the GGG / TmIG interface is the source of the iDMI in this system. Our work demonstrates that SOT and DMI can originate from two different interfaces, which enables independent optimization of DMI and SOT for advanced chiral spintronics with low damping magnetic insulators.

cond-mat.mtrl-sci↗

arXiv2020

An insulating doped antiferromagnet with low magnetic symmetry as a room temperature spin conduit

We report room temperature long-distance spin transport of magnons in antiferromagnetic thin film hematite doped with Zn. The additional dopants significantly alter the magnetic anisotropies, resulting in a complex equilibrium spin structure that is capable of efficiently transporting spin angular momentum at room temperature without the need for a well-defined, pure easy-axis or easy-plane anisotropy. We find intrinsic magnon spin-diffusion lengths of up to 1.5 μm, and magnetic domain governed decay lengths of 175 nm for the low frequency magnons, through electrical transport measurements demonstrating that the introduction of non-magnetic dopants does not strongly reduce the transport length scale showing that the magnetic damping of hematite is not significantly increased. We observe a complex field dependence of the non-local signal independent of the magnetic state visible in the local magnetoresistance and direct magnetic imaging of the antiferromagnetic domain structure. We explain our results in terms of a varying and applied-field-dependent ellipticity of the magnon modes reaching the detector electrode allowing us to tune the spin transport.

cond-mat.mes-hall↗