Xuefei Miao

Topologically protected magnetic (anti)merons have garnered widespread attention owing to their promising potential use as long‐range information carriers in spintronic devices. However, (anti)merons usually emerge only within a narrow temperature range below room temperature and/or under an external magnetic field, hindering the development of such applications. Here, we report the direct observation of spontaneous isolated (anti)meron pairs and (anti)meron chains without the need for external magnetic fields over a wide temperature range across room temperature (313–80 K) in a Fe ₂ P‐type Mn‐Fe‐P‐Si material with easy‐plane magnetic anisotropy. Spontaneous isolated (anti)meron pairs are induced by a magnetoelastic transition from a paramagnetic to ferromagnetic state and subsequently evolve into (anti)meron chains upon cooling. These spontaneous (anti)merons exhibit distinct processes of creation, movement, and annihilation in response to variations in temperature and magnetic field, demonstrating their controllability. Through a combination of first‐principles calculations, neutron powder diffraction, and micromagnetic simulations, we reveal that easy‐plane magnetic anisotropy plays a pivotal role in the spontaneous generation and stabilization of topological (anti)merons in this system. Our findings provide an alternative way to generate spontaneous topological spin textures utilizing easy‐plane magnetic anisotropy and magnetoelastic transition, and establish magnetoelastic coupling materials as a versatile platform for future spintronics devices.

Magnetocaloric high-entropy alloys (HEAs) have recently garnered significant interest owing to their potential applications in magnetic refrigeration, offering a wide working temperature range and large refrigerant capacity. In this study, we thoroughly investigated the structural, magnetic, and magnetocaloric properties of equiatomic GdDyHoErTm HEAs. The as-cast alloy exhibits a single hexagonal phase, a randomly distributed grain orientation, and complex magnetism. In particular, multiple magnetic phase transitions occur over a wide temperature range in this rare-earth HEA, which is attributed to the diverse magnetic properties of the constituent rare-earth elements. Accordingly, a table-like magnetocaloric effect (the maximum magnetic entropy change of 7.5 J/kg K at 5 T) is achieved in the temperature range of 27-175 K, leading to a giant refrigerant capacity of 923 J/kg and relative cooling power of 1110 J/kg. Our findings in the rare-earth HEAs with multiple magnetic phase transitions open up a pathway to further develop high-performance magnetocaloric materials in the field of cryogenic magnetic refrigeration.

Magnetic cooling, a solid-state refrigeration technology based on the magnetocaloric effect, has attracted significant attention in space cooling due to its high energy-efficiency and environmental friendliness. Transition metal-based magnetocaloric materials (MCMs) with the merit of low-cost have emerged as promising candidates for efficient magnetic refrigeration applications. This review explores the intricate relationship between microstructure and multiple properties (e.g. magnetocaloric properties, mechanical stability, thermal conductivity, and functional reversibility) of these materials. A variety of microstructural manipulation approaches (e.g. crystallographic texture, precipitates, micropores, atomic-scale defects, size effect, and composites) are examined for their effects on the comprehensive performance of MCMs. We show that microstructure design provides an effective tool to achieve excellent performance in multiple aspects, which may facilitate the commercialization of transition-metal based MCMs.

Owing to their exceptional properties, high‐entropy alloys (HEAs) and high‐entropy materials have emerged as promising research areas and shown diverse applications. Here, the recent advances in the field are comprehensively reviewed, organized into five sections. The first section introduces the background of HEAs, covering their definition, significance, application prospects, basic properties, design principles, and microstructure. The subsequent section focuses on cutting‐edge high‐entropy structural materials, highlighting developments such as nanostructured alloys, grain boundary engineering, eutectic systems, cryogenic alloys, thin films, micro‐nano‐lattice structures, additive manufacturing, high entropy metallic glasses, nano‐precipitate strengthened alloys, composition modulation, alloy fibers, and refractory systems. In the following section, the emphasis shifts to functional materials, exploring HEAs as catalysts, magneto‐caloric materials, corrosion‐resistant alloys, radiation‐resistant alloys, hydrogen storage systems, and materials for biomedicine. Additionally, the review encompasses functional high‐entropy materials outside the realm of alloys, including thermoelectric, quantum dots, nanooxide catalysts, energy storage materials, negative thermal expansion ceramics, and high‐entropy wave absorption materials. The paper concludes with an outlook, discussing future directions and potential growth areas in the field. Through this comprehensive review, researchers, engineers, and scientists may gain valuable insights into the recent progress and opportunities for further exploration in the exciting domains of high‐entropy alloys and functional materials.

The development of zero and negative thermal expansion (i.e., ZTE and NTE) materials is of crucial importance to the control of undesirable thermal expansion for high‐precision devices. In the present work, ZTE and NTE were obtained in directionally‐solidified Mn _x Fe _{5– x} Si ₃ alloys with a strong texture, in striking contrast to positive thermal expansion in their isotropic counterparts. Magnetometry and in‐situ X‐ray diffraction (XRD) measurements were performed to uncover the origin of the anomalous thermal expansion. Magnetic measurements indicate a strong easy‐plane magnetocrystalline anisotropy in the textured samples, where the magnetic moments are aligned within the ab plane of the hexagonal structure. Temperature‐dependent XRD on the x = 1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition. As a result, the macroscopic ZTE (~ 0.22 × 10 ^–6 K ⁻¹ ) in the x = 1 sample can be attributed to the microscopic magneto volume effect within the ab plane, which is realized by the introduction of the ‐textured microstructure. Besides, the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x = 1.5 and 2 samples. Additionally, textured x = 1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly‐oriented grains. Consequently, this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.