Topological transformation of synthetic ferromagnetic skyrmions: thermal assisted switching of helicity by spin-orbit torque.

This study demonstrates the controllable switching of skyrmion helicity using spin-orbit torque, enhanced by thermal effects. Electric current pulses applied to a [Pt/Co]/Ru/[Co/Pt] multilayer stripe drive skyrmions in a direction opposite to the current flow. Continuous pulsing results in an unexpected reversal of skyrmion motion.

Acoustic Wave-Induced FeRh Magnetic Phase Transition and Its Application in Antiferromagnetic Pattern Writing and Erasing.

We explore the FeRh magnetic phase transition (MPT) and magnetic phase domain (MPD) with the introduction of surface acoustic waves (SAWs). The effects of the SAW pulses with different pulse widths and powers on resistance-temperature loops are investigated, revealing that the SAW can reduce the thermal hysteresis. Meanwhile, the SAW-induced comb-like antiferromagnetic (AFM) phase domains are observed.

Generation of skyrmions by combining thermal and spin-orbit torque: breaking half skyrmions into skyrmions.

Skyrmions, swirling spin textures with topologically protected stability and low critical driven-current density, can be generated from the stripe domain with current pulses, bringing them closer to practical applications in racetrack memory. However, the mechanism of this topological transition from the stripe domain to the skyrmion remains unclear because the transition process occurs at a nanosecond timescale, giving rise to difficulties in observing this process using imaging tools. In this study, we controlled the domain wall - skyrmion transition by combining Joule heating with spin-orbit torque (SOT) and experimentally observed the details of this process, by which we confirmed the mechanism: the spatial variation of the topological charge density induces half skyrmions branching from the stripe domains, and these half skyrmions overcome the surface tension and break away from the stripe domain, resulting in the generation of skyrmions.

Magnetic Skyrmions above Room Temperature in a van der Waals Ferromagnet FeGaTe.

2D van der Waals (vdW) ferromagnetic crystals are a promising platform for innovative spintronic devices based on magnetic skyrmions, thanks to their high flexibility and atomic thickness stability. However, room-temperature skyrmion-hosting vdW materials are scarce, which poses a challenge for practical applications. In this study, a chemical vapor transport (CVT) approach is employed to synthesize FeGaTe crystals and room-temperature Néel skyrmions are observed in FeGaTe nanoflakes above 58 nm in thickness through in situ Lorentz transmission electron microscopy (L-TEM).

Strain-Induced Reversible Motion of Skyrmions at Room Temperature.

Magnetic skyrmions are topologically protected swirling spin textures with great potential for future spintronic applications. The ability to induce skyrmion motion using mechanical strain not only stimulates the exploration of exotic physics but also affords the opportunity to develop energy-efficient spintronic devices. However, the experimental realization of strain-driven skyrmion motion remains a formidable challenge.

Current-Induced Reversible Split of Elliptically Distorted Skyrmions in Geometrically Confined Fe Sn Nanotrack.

Skyrmions are swirling spin textures with topological characters promising for future spintronic applications. Skyrmionic devices typically rely on the electrical manipulation of skyrmions with a circular shape. However, manipulating elliptically distorted skyrmions can lead to numerous exotic magneto-electrical functions distinct from those of conventional circular skyrmions, significantly broadening the capability to design innovative spintronic devices.

Magnetic Skyrmions with Unconventional Helicity Polarization in a Van Der Waals Ferromagnet.

Skyrmion helicity, which defines the spin swirling direction, is a fundamental parameter that may be utilized to encode data bits in future memory devices. Generally, in centrosymmetric ferromagnets, dipole skyrmions with helicity of -π/2 and π/2 are degenerate in energy, leading to equal populations of both helicities. On the other hand, in chiral materials where the Dzyaloshinskii-Moriya interaction (DMI) prevails and the dipolar interaction is negligible, only a preferred helicity is selected by the type of DMI.

Superposition of Emergent Monopole and Antimonopole in CoTb Thin Films.

A three-dimensional singular point that consists of two oppositely aligned emergent monopoles is identified in continuous CoTb thin films, as confirmed by complementary techniques of resonant elastic x-ray scattering, Lorentz transmission electron microscopy, and scanning transmission x-ray microscopy. This new type of topological defect can be regarded as a superposition of an emergent magnetic monopole and an antimonopole, around which the source and drain of the magnetic flux overlap in space. We experimentally prove that the observed spin twist seen in Lorentz transmission electron microscopy reveals the cross section of the superimposed three-dimensional structure, providing a straightforward strategy for the observation of magnetic singularities.

Chiral Helimagnetism and One-Dimensional Magnetic Solitons in a Cr-Intercalated Transition Metal Dichalcogenide.

Chiral magnets endowed with topological spin textures are expected to have promising applications in next-generation magnetic memories. In contrast to the well-studied 2D or 3D magnetic skyrmions, the authors report the discovery of 1D nontrivial magnetic solitons in a transition metal dichalcogenide 2H-TaS via precise intercalation of Cr elements. In the synthetic Cr TaS (CTS) single crystal, the coupling of the strong spin-orbit interaction from TaS and the chiral arrangement of the magnetic Cr ions evoke a robust Dzyaloshinskii-Moriya interaction.

Berry Phase Engineering in SrRuO/SrIrO/SrTiO Superlattices Induced by Band Structure Reconstruction.

The Berry phase, which reveals the intimate geometrical structure underlying quantum mechanics, plays a central role in the anomalous Hall effect. In this work, we observed a sign change of Berry curvatures at the interface between the ferromagnet SrRuO (SRO) layer and the SrIrO (SIO) layer with strong spin-orbit coupling. The negative Berry curvature at the interface, induced by the strongly spin-orbit-coupled Ir 5d bands near the Fermi level, makes the SRO/SIO interface different from the SRO layer that has a positive Berry curvature.

Electron Beam Lithography of Magnetic Skyrmions.

The emergence of magnetic skyrmions, topological spin textures, has aroused tremendous interest in studying the rich physics related to their topology. While skyrmions promise high-density and energy-efficient magnetic memory devices for information technology, the manifestation of their nontrivial topology through single skyrmions and ordered and disordered skyrmion lattices could also give rise to many fascinating physical phenomena, such as chiral magnon and skyrmion glass states. Therefore, generating skyrmions at designated locations on a large scale, while controlling the skyrmion patterns, is the key to advancing topological magnetism.

Magnetotransport Mechanism of Individual Nanostructures Direct Magnetoresistance Measurement SEM.

The accurate magnetoresistance (MR) measurement of individual nanostructures is essential and important for either the enrichment of fundamental knowledge of the magnetotransport mechanism or the facilitation of desired design of magnetic nanostructures for various technological applications. Herein, we report a deep investigation on the magnetotransport mechanism of a single CoCu/Cu multilayered nanowire direct MR measurement using our invented magnetotransport instrument scanning electron microscope. Off-axis electron holography experiments united with micromagnetic simulation prove that the CoCu layers in CoCu/Cu multilayered nanowires form a single-domain structure, in which the alignment of magnetic moments is mainly determined by shape anisotropy.

Néel-type skyrmion in WTe/FeGeTe van der Waals heterostructure.

The promise of high-density and low-energy-consumption devices motivates the search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. At the same time, recently discovered long-range intrinsic magnetic orders in the two-dimensional van der Waals materials provide a new platform for the discovery of novel physics and effects. Here we demonstrate the Dzyaloshinskii-Moriya interaction and Néel-type skyrmions are induced at the WTe/FeGeTe interface.

Direct imaging of an inhomogeneous electric current distribution using the trajectory of magnetic half-skyrmions.

The direct imaging of current density vector distributions in thin films has remained a daring challenge. Here, we report that an inhomogeneous current distribution can be mapped directly by the trajectories of magnetic half-skyrmions driven by an electrical current in Pt/Co/Ta trilayer, using polar magneto-optical Kerr microscopy. The half-skyrmion carries a topological charge of 0.

Current-Induced Helicity Reversal of a Single Skyrmionic Bubble Chain in a Nanostructured Frustrated Magnet.

Helicity indicates the in-plane magnetic-moment swirling direction of a skyrmionic configuration. The ability to reverse the helicity of a skyrmionic bubble via purely electrical means has been predicted in frustrated magnetic systems; however, it has been challenging to observe this experimentally. The current-driven helicity reversal of the skyrmionic bubble in a nanostructured frustrated Fe Sn magnet is experimentally demonstrated.

Electric-Field-Enhanced Bulk Perpendicular Magnetic Anisotropy in GdFe/Pb(MgNb)TiO Multiferroic Heterostructure.

Perpendicular magnetic anisotropy is important for increasing the information storage density in the perpendicular magnetic recording media, and for rare-earth-transition-metal alloys with bulk perpendicular magnetic anisotropy that generate great research interest due to their abundant interesting phenomena, such as fast domain wall motion and skyrmion. Here, we deposit amorphous GdFe ferrimagnetic films on Pb(MgNb)TiO ferroelectric substrate and investigate the effect of electric-field-induced piezostrain on its bulk perpendicular magnetic anisotropy. The anomalous Hall effect and polar Kerr image measurements suggest an enhanced bulk perpendicular magnetic anisotropy by electric field, which originates from a positive magnetoelastic anisotropy due to the positive magnetostriction coefficient of the GdFe film and the electric-field-induced tensile strain along the axis in Pb(MgNb)TiO ferroelectric substrate.

Manipulating the Topology of Nanoscale Skyrmion Bubbles by Spatially Geometric Confinement.

The discovery of magnetic skyrmion bubbles in centrosymmetric magnets has been receiving increasing interest from the research community, due to the fascinating physics of topological spin textures and its possible applications to spintronics. However, key challenges remain, such as how to manipulate the nucleation of skyrmion bubbles to exclude the trivial bubbles or metastable skyrmion bubbles that usually coexist with skyrmion bubbles in the centrosymmetric magnets. Here, we report having performed this task by applying spatially geometric confinement to a centrosymmetric frustrated FeSn magnet.

Spin-momentum locking and spin-orbit torques in magnetic nano-heterojunctions composed of Weyl semimetal WTe.

Spin-orbit torque has recently been intensively investigated for the purposes of manipulating the magnetization in magnetic nano-devices and understanding fundamental physics. Therefore, the search for novel materials or material combinations that exhibit a strong enough spin-torque effect has become one of the top priorities in this field of spintronics. Weyl semimetal, a new topological material that features open Fermi arc with strong spin-orbit coupling and spin-momentum locking effect, is naturally expected to exhibit an enhanced spin-torque effect in magnetic nano-devices.