Yangkun He

Magnetic skyrmions are vortex-like spin textures that exhibit remarkable emergent phenomena and hold great promise for applications in spintronics, magnonic devices, and neuromorphic computing. Typically, these spin textures are formed in magnetic samples through the application of magnetic fields on a ground state helical phase. However, achieving the formation of zero-field skyrmions, without the need of prior field-cooling, has remained a significant challenge. Here, using real-space Lorentz transmission electron microscopy, we directly observe the spontaneous emergence of skyrmions beyond room temperature in a centrosymmetric crystal of boron-doped CrTe without the presence of external magnetic fields. These skyrmions exhibit robust stability over a large temperature range in zero field and various specimen thicknesses. We nevertheless demonstrate that a field-cooling process can control the density and arrangement of metastable zero-field skyrmions, which is confirmed by micromagnetic simulations. The stabilization of field-free spontaneous skyrmions beyond ambient temperature holds implications for nonvolatile memory systems.

Metastable materials attract considerable interest due to their superior properties. However, the trade-off between remarkable properties and stability has limited their development. Taking the metastable SmFe12 phase as an example, phase stability is achieved at the cost of reduced saturation magnetization. Here, we propose three stabilizing mechanisms and a site-selective cooperative doping strategy that overcome the inherent trade-off between performance and stability for SmFe12 magnet. The crystal structure can be stabilized by size matching, strengthening chemical bonds and regulation of the valence electron concentration. The proposed stabilizing mechanisms were applied to guide site-selective co-doping at distinct crystallographic sites in 1:12 compounds. By co-doping Zr, Co, Ti, and Si, single-phase stability was achieved while the saturation magnetization was enhanced from 1.21 T to 1.51 T. Our work points out a pathway to simultaneously achieve high performance and good phase stability in metastable materials by multiple stabilizing mechanisms.

Rare‐earth permanent magnets are vital in modern industries, but imbalanced rare‐earth consumption threatens their sustainability, driving the need for next‐generation solutions. The 1:12‐type SmFe magnets, with the highest theoretical magnetic energy product, show significant potential. This study reviews recent advancements in 1:12‐type SmFe magnets, analyzing factors affecting their stability, intrinsic magnetic properties, and underlying mechanisms. It also examines how microstructure influences extrinsic properties like remanence and coercivity, and discusses fabrication techniques and their impact on performance. Additionally, the study explores progress in controlling skyrmions in the 1:12 phase, investigating the effects of composition, temperature, and magnetic fields. Finally, it highlights potential applications and future research directions.

Fully compensated ferrimagnets are attracting increasing attention for spintronics. Here we report a series of Mn 4 − x Ga _x N ferrimagnetic thin films grown on (100)-oriented MgO by magnetron sputtering. A small tetragonal distortion with c / a = 0.99 leads to perpendicular magnetic anisotropy with a [001] easy axis. The magnetisation decreases with increasing Ga content up to x = 0.18, where the magnetic moment is close to zero at room temperature. It increases with further increase of x, indicating the magnetic compensation composition has been crossed and the dominant sublattice has switched from Mn on the corner sites, where it is progressively replaced by nonmagnetic Ga, to noncollinear Mn on the face-centered sites. Compensation found at 235 K in a remanent scan of the x = 0.18 film is confirmed by measurements of the anomalous Hall effect and interpolation of the inverse coercivity. This work establishes the conditions for thin film growth of Mn 4 − x Ga _x N that could be used for room-temperature ferrimagnetic spintronics. The behaviour of thin films is compared with that of bulk material.

Iron‐rich 2:17‐type SmCo magnets are expected to achieve high performance and relatively low cost. However, inhomogeneous cellular structures usually exist in iron‐rich magnets, resulting in a drastic reduction in coercivity and energy product. Herein, a strategy is proposed to regulate the dislocation by decreasing the Sm content and extending the solid‐solution duration in precursor of iron‐rich SmCo magnet. High‐density dislocations in precursor contributed to 1:5H nucleation, leading to uniform cellular structures in final magnets. As a result, a remarkable intrinsic coercivity of 1.50 T and one of the highest remanences (1.24 T) are simultaneously achieved in the iron‐rich Sm₂₅Co₄₂Fe₂₆Cu₅Zr₂ (wt%) magnet. This study provides valuable insights into the design and development of iron‐rich 2:17‐type SmCo magnets.

DOI: https://doi.org/10.1103/PhysRevLett.131.089701

Fully compensated ferrimagnetic half metals have attracted great attention in spintronics. Unlike many previous calculations based on hypothetical ordered alloys, here we look for existing solid solution series taking as an example Co_1−xCr_xS₂. Calculations find that a low-spin state for Cr that matches early experiments and a fully compensated ferrimagnetic half metal with Curie temperature above room temperature is found at x ≈ 0.33. Our study demonstrates the method of combining two half metals with light and heavy 3d metals in a solid solution to achieve compensation, where atomic disorder does not destroy the desired properties.

Skyrmionic materials hold the potential for future information technologies, such as racetrack memories. Key to that advancement are systems that exhibit high tunability and scalability, with stored information being easy to read and write by means of all-electrical techniques. Topological magnetic excitations such as skyrmions and antiskyrmions, give rise to a characteristic topological Hall effect. However, the electrical detection of antiskyrmions, in both thin films and bulk samples has been challenging to date. Here, we apply magneto-optical microscopy combined with electrical transport to explore the antiskyrmion phase as it emerges in crystalline mesoscale structures of the Heusler magnet Mn_1.4PtSn. We reveal the Hall signature of antiskyrmions in line with our theoretical model, comprising anomalous and topological components. We examine its dependence on the vertical device thickness, field orientation, and temperature. Our atomistic simulations and experimental anisotropy studies demonstrate the link between antiskyrmions and a complex magnetism that consists of competing ferromagnetic, antiferromagnetic, and chiral exchange interactions, not captured by micromagnetic simulations.