Relativistic Spin-Lattice Interaction Compatible with Discrete Translation Symmetry in Solids.

Recent interest in orbital angular momentum has led to a rapid expansion of research on spin-orbit coupling effects in solids, while also highlighting significant technical challenges. The breaking of rotational symmetry renders the orbital angular momentum operator ill defined, causing conceptual and computational issues in describing orbital motion. To address these issues, here we propose an alternative framework.

Magnetization switching driven by magnonic spin dissipation.

Efficient control of magnetization in ferromagnets is crucial for high-performance spintronic devices. Magnons offer a promising route to achieve this objective with reduced Joule heating and minimized power consumption. While most research focuses on optimizing magnon transport with minimal dissipation, we present an unconventional approach that exploits magnon dissipation for magnetization control, rather than mitigating it.

Intrinsic and Extrinsic Unity for Chiral-Spin Alignment and Charge-to-Spin Conversion Induced by the Rashba-Edelstein Effect.

Reducing the dimensionality in layered materials typically yields properties distinct from bulk properties. In systems with broken inversion symmetry, strong spin-orbit coupling induces relativistic electron interactions such as the Rashba-Edelstein effect (REE). Initially proposed in two-dimensional magnets, applying the REE theory to real three-dimensional systems poses challenges, necessitating experimental validation.

Orbital Pumping Incorporating Both Orbital Angular Momentum and Position.

We develop a theory of adiabatic orbital pumping, highlighting qualitative differences from spin pumping. An oscillating magnetic field pumps not only orbital angular momentum current, but also orbital angular position current. The latter, which has no spin counterpart, underscores the incompleteness of existing orbital torque theories.

Orbital Diffusion, Polarization, and Swapping in Centrosymmetric Metals.

We propose a general theory of charge, spin, and orbital diffusion based on Keldysh formalism. Our findings indicate that the diffusivity of orbital angular momentum in metals is much lower than that of spin or charge due to the strong orbital intermixing in crystals. Furthermore, our theory introduces the concept of "spin-orbit polarization" by which a pure orbital (spin) current induces a longitudinal spin (orbital) current, a process as efficient as spin polarization in ferromagnets.

Giant Modulation of Magnetoresistance in a Van Der Waals Magnet by In-Plane Current Injection.

Efficient magnetization control is a central issue in magnetism and spintronics. Particularly, there are increasing demands for manipulation of magnetic states in van der Waals (vdW) magnets with unconventional functionalities. However, the electrically induced phase transition between ferromagnetic-to-antiferromagnetic states without external magnetic field is yet to be demonstrated.

Colossal Shift Currents in Band-Inverted Bi Nanotubes Driven by the Interplay of Curvature and Spin-Orbit Coupling.

The concept of non-trivial electronic structure combined with reduced dimensionality presents a promising strategy for advancing optical applications and energy harvesting technologies. Symmetry breaking in low dimensional system enables the emergence of non-linear optical responses, which are greatly amplified by the singular points of band inversion. Here, using first-principles calculations, the significant enhancement of the shift current in Bi nanotubes is investigated, driven by the combined effects of 1D geometry and non-trivial band order.

Chiral Damping of Magnons.

Chiral magnets have garnered significant interest due to the emergence of unique phenomena prohibited in inversion-symmetric magnets. While the equilibrium characteristics of chiral magnets have been extensively explored through the Dzyaloshinskii-Moriya interaction (DMI), nonequilibrium properties like magnetic damping have received comparatively less attention. We present the inaugural direct observation of chiral damping through Brillouin light scattering (BLS) spectroscopy.

Metamagnetic transition and meta-stable magnetic state in Co-doped FeGaTe.

The transition between the ferromagnetic (FM) and anti-ferromagnetic (AFM) phases in van der Waals (vdW) magnets has been extensively studied since the discovery of vdW magnets, due to the importance of both transitions within a single material. Recently, among vdW magnets, FeGaTe (FGaT) has garnered significant attention for its robust FM properties that remain stable above room temperature. Also, the FM to AFM phase transition in this material has been achieved through substitutional Co-atom doping at Fe sites.

Non-volatile Fermi level tuning for the control of spin-charge conversion at room temperature.

Current silicon-based CMOS devices face physical limitations in downscaling size and power loss, restricting their capability to meet the demands for data storage and information processing of emerging technologies. One possible alternative is to encode the information in a non-volatile magnetic state and manipulate this spin state electronically, as in spintronics. However, current spintronic devices rely on the current-driven control of magnetization, which involves Joule heating and power dissipation.

Additive roles of antiferromagnetically coupled elements in the magnetic proximity effect in the GdFeCo/Pt system.

Interfacial magnetic interactions between different elements are the origin of various spin-transport phenomena in multi-elemental magnetic systems. We investigate the coupling between the magnetic moments of the rare-earth, transition-metal, and heavy-metal elements across the interface in a GdFeCo/Pt thin film, an archetype system to investigate ferrimagnetic spintronics. The Pt magnetic moments induced by the antiferromagnetically aligned FeCo and Gd moments are measured using element-resolved x-ray measurements.

Field-free switching of perpendicular magnetization by two-dimensional PtTe/WTe van der Waals heterostructures with high spin Hall conductivity.

The key challenge of spin-orbit torque applications lies in exploring an excellent spin source capable of generating out-of-plane spins while exhibiting high spin Hall conductivity. Here we combine PtTe for high spin conductivity and WTe for low crystal symmetry to satisfy the above requirements. The PtTe/WTe bilayers exhibit a high in-plane spin Hall conductivity σ ≈ 2.

Optoelectronic Manifestation of Orbital Angular Momentum Driven by Chiral Hopping in Helical Se Chains.

Chiral materials have garnered significant attention in the field of condensed matter physics. Nevertheless, the magnetic moment induced by the chiral spatial motion of electrons in helical materials, such as elemental Te and Se, remains inadequately understood. In this work, we investigate the development of quantum angular momentum enforced by chirality by using static and time-dependent density functional theory calculations for an elemental Se chain.

Enhanced spin Seebeck effect via oxygen manipulation.

Spin Seebeck effect (SSE) refers to the generation of an electric voltage transverse to a temperature gradient via a magnon current. SSE offers the potential for efficient thermoelectric devices because the transverse geometry of SSE enables to utilize waste heat from a large-area source by greatly simplifying the device structure. However, SSE suffers from a low thermoelectric conversion efficiency that must be improved for widespread application.

Bulk Rashba-Type Spin Splitting in Non-Centrosymmetric Artificial Superlattices.

Spin current, converted from charge current via spin Hall or Rashba effects, can transfer its angular momentum to local moments in a ferromagnetic layer. In this regard, the high charge-to-spin conversion efficiency is required for magnetization manipulation for developing future memory or logic devices including magnetic random-access memory. Here, the bulk Rashba-type charge-to-spin conversion is demonstrated in an artificial superlattice without centrosymmetry.

Universal Hopping Motion Protected by Structural Topology.

A scaling law elucidates the universality in nature, presiding over many physical phenomena which seem unrelated. Thus, exploring the universality class of scaling law in a particular system enlightens its physical nature in relevance to other systems and sometimes unearths an unprecedented new dynamic phase. Here, the dynamics of weakly driven magnetic skyrmions are investigated, and its scaling law is compared with the motion of a magnetic domain wall (DW) creep.

Spin Swapping Effect of Band Structure Origin in Centrosymmetric Ferromagnets.

We theoretically demonstrate the spin swapping effect of band structure origin in centrosymmetric ferromagnets. It is mediated by an orbital degree of freedom but does not require inversion asymmetry or impurity spin-orbit scattering. Analytic and tight-binding models reveal that it originates mainly from k points where bands with different spins and different orbitals are nearly degenerate, and thus it has no counterpart in normal metals.

Orbital Dynamics in Centrosymmetric Systems.

Orbital dynamics in time-reversal-symmetric centrosymmetric systems is examined theoretically. Contrary to common belief, we demonstrate that many aspects of orbital dynamics are qualitatively different from spin dynamics because the algebraic properties of the orbital and spin angular momentum operators are different. This difference generates interesting orbital responses, which do not have spin counterparts.

Electric-field control of field-free spin-orbit torque switching via laterally modulated Rashba effect in Pt/Co/AlO structures.

Spin-orbit coupling effect in structures with broken inversion symmetry, known as the Rashba effect, facilitates spin-orbit torques (SOTs) in heavy metal/ferromagnet/oxide structures, along with the spin Hall effect. Electric-field control of the Rashba effect is established for semiconductor interfaces, but it is challenging in structures involving metals owing to the screening effect. Here, we report that the Rashba effect in Pt/Co/AlO structures is laterally modulated by electric voltages, generating out-of-plane SOTs.

Interface Engineering of Magnetic Anisotropy in van der Waals Ferromagnet-based Heterostructures.

Interface engineering is an effective approach to tune the magnetic properties of van der Waals (vdW) magnets and their heterostructures. The prerequisites for the practical utilization of vdW magnets and heterostructures are a quantitative analysis of their magnetic anisotropy and the ability to modulate their interfacial properties, which have been challenging to achieve with conventional methods. Here we characterize the magnetic anisotropy of FeGeTe layers by employing the magnetometric technique based on anomalous Hall measurements and confirm its intrinsic nature.

Exchange Bias in Weakly Interlayer-Coupled van der Waals Magnet FeGeTe.

van der Waals (vdW) magnetic materials provide an ideal platform to study low-dimensional magnetism. However, observations of magnetic characteristics of these layered materials truly distinguishing them from conventional magnetic thin film systems have been mostly lacking. In an effort to investigate magnetic properties unique to vdW magnetic materials, we examine the exchange bias effect, a magnetic phenomenon emerging at the ferromagnetic-antiferromagnetic interface.

Bloch Chirality Induced by an Interlayer Dzyaloshinskii-Moriya Interaction in Ferromagnetic Multilayers.

Chiral spin textures stabilized by the interfacial Dzyaloshinkii-Moriya interaction, such as skyrmions and homochiral domain walls, have been shown to exhibit qualities that make them attractive for their incorporation in a variety of spintronic devices. However, for thicker multilayer films, mixed textures occur in which an achiral Bloch component coexists with a chiral Néel component of the domain wall to reduce the demagnetization field at the film surface. We show that an interlayer Dzyaloshinkii-Moriya interaction can break the degeneracy between Bloch chiralities.

Generalized Spin Drift-Diffusion Formalism in the Presence of Spin-Orbit Interaction of Ferromagnets.

We generalize the spin drift-diffusion formalism by considering spin-orbit interaction of a ferromagnet, which generates transverse spin currents in the ferromagnet. We consider quantum-mechanical transport of transverse spins in a spin-orbit coupled ferromagnet and develop a generalized drift-diffusion equation and boundary condition. By combining them, we identify previously unrecognized spin transport phenomena in heterostructures including ferromagnets.