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1. Electric-field control of skyrmions in multiferroic heterostructure via magnetoelectric coupling

   https://doi.org/10.1038/s41467-020-20528-y  

   Ba, You; Zhuang, Shihao; Zhang, Yike; Wang, Yutong; Gao, Yang; Zhou, Hengan; Chen, Mingfeng; Sun, Weideng; Liu, Quan; Chai, Guozhi; et al (December 2021, Nature Communications)

   null (Ed.)

   Abstract Room-temperature skyrmions in magnetic multilayers are considered to be promising candidates for the next-generation spintronic devices. Several approaches have been developed to control skyrmions, but they either cause significant heat dissipation or require ultrahigh electric fields near the breakdown threshold. Here, we demonstrate electric-field control of skyrmions through strain-mediated magnetoelectric coupling in ferromagnetic/ferroelectric multiferroic heterostructures. We show the process of non-volatile creation of multiple skyrmions, reversible deformation and annihilation of a single skyrmion by performing magnetic force microscopy with in situ electric fields. Strain-induced changes in perpendicular magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction strength are characterized experimentally. These experimental results, together with micromagnetic simulations, demonstrate that strain-mediated magnetoelectric coupling (via strain-induced changes in both the perpendicular magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction is responsible for the observed electric-field control of skyrmions. Our work provides a platform to investigate electric-field control of skyrmions in multiferroic heterostructures and paves the way towards more energy-efficient skyrmion-based spintronics. 

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2. Ordering of room-temperature magnetic skyrmions in a polar van der Waals magnet

   https://doi.org/10.1038/s41467-023-39442-0  

   Meisenheimer, Peter; Zhang, Hongrui; Raftrey, David; Chen, Xiang; Shao, Yu-Tsun; Chan, Ying-Ting; Yalisove, Reed; Chen, Rui; Yao, Jie; Scott, Mary C.; et al (June 2023, Nature Communications)

   Abstract Control and understanding of ensembles of skyrmions is important for realization of future technologies. In particular, the order-disorder transition associated with the 2D lattice of magnetic skyrmions can have significant implications for transport and other dynamic functionalities. To date, skyrmion ensembles have been primarily studied in bulk crystals, or as isolated skyrmions in thin film devices. Here, we investigate the condensation of the skyrmion phase at room temperature and zero field in a polar, van der Waals magnet. We demonstrate that we can engineer an ordered skyrmion crystal through structural confinement on theμm scale, showing control over this order-disorder transition on scales relevant for device applications. 

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3. Room‐Temperature Magnetic Skyrmions and Large Topological Hall Effect in Chromium Telluride Engineered by Self‐Intercalation

   https://doi.org/10.1002/adma.202205967  

   Zhang, Chenhui; Liu, Chen; Zhang, Junwei; Yuan, Youyou; Wen, Yan; Li, Yan; Zheng, Dongxing; Zhang, Qiang; Hou, Zhipeng; Yin, Gen; et al (November 2022, Advanced Materials)

   Abstract Room‐temperature magnetic skyrmion materials exhibiting robust topological Hall effect (THE) are crucial for novel nano‐spintronic devices. However, such skyrmion‐hosting materials are rare in nature. In this study, a self‐intercalated transition metal dichalcogenide Cr_1+xTe₂with a layered crystal structure that hosts room‐temperature skyrmions and exhibits large THE is reported. By tuning the self‐intercalate concentration, a monotonic control of Curie temperature from 169 to 333 K and a magnetic anisotropy transition from out‐of‐plane to the in‐plane configuration are achieved. Based on the intercalation engineering, room‐temperature skyrmions are successfully created in Cr_1.53Te₂with a Curie temperature of 295 K and a relatively weak perpendicular magnetic anisotropy. Remarkably, a skyrmion‐induced topological Hall resistivity as large as ≈106 nΩ cm is observed at 290 K. Moreover, a sign reversal of THE is also found at low temperatures, which can be ascribed to other topological spin textures having an opposite topological charge to that of the skyrmions. Therefore, chromium telluride can be a new paradigm of the skyrmion material family with promising prospects for future device applications. 

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4. Single skyrmion true random number generator using local dynamics and interaction between skyrmions

   https://doi.org/10.1038/s41467-022-28334-4  

   Wang, Kang; Zhang, Yiou; Bheemarasetty, Vineetha; Zhou, Shiyu; Ying, See-Chen; Xiao, Gang (February 2022, Nature Communications)

   Abstract Magnetic skyrmions are of great interest to both fundamental research and applications in post-von-Neumann computing devices. The successful implementation of skyrmionic devices requires functionalities of skyrmions with effective controls. Here we show that the local dynamics of skyrmions, in contrast to the global dynamics of a skyrmion as a whole, can be introduced to provide effective functionalities for versatile computing. A single skyrmion interacting with local pinning centres under thermal effects can fluctuate in time and switch between a small-skyrmion and a large-skyrmion state, thereby serving as a robust true random number generator for probabilistic computing. Moreover, neighbouring skyrmions exhibit an anti-correlated coupling in their fluctuation dynamics. Both the switching probability and the dynamic coupling strength can be tuned by modifying the applied magnetic field and spin current. Our results could lead to progress in developing magnetic skyrmionic devices with high tunability and efficient controls. 

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5. Strain-mediated voltage-controlled switching of magnetic skyrmions in nanostructures

   https://doi.org/10.1038/s41524-018-0119-2  

   Hu, Jia-Mian; Yang, Tiannan; Chen, Long-Qing (November 2018, npj Computational Materials)

   Abstract Magnetic skyrmions are swirling spin structures stabilized typically by the Dyzaloshinskii-Moriya interaction. The existing control of magnetic skyrmions has often relied on the use of an electric current, which may cause overheating in densely packed devices. Here we demonstrate, using phase-field simulations, that an isolated Néel skyrmion in a magnetic nanodisk can be repeatedly created and deleted by voltage-induced strains from a juxtaposed piezoelectric. Such a skyrmion switching is non-volatile, and consumes only ~0.5 fJ per switching which is about five orders of magnitude smaller than that by current-induced spin-transfer-torques. It is found that the strain-mediated skyrmion creation occurs through an intermediate vortex-like spin structure, and that the skyrmion deletion occurs though a homogenous shrinkage during which the Néel wall is temporarily transformed to a vortex-wall. These findings are expected to stimulate experimental research into strain-mediated voltage control of skyrmions, as well as other chiral spin structures for low-power spintronics. 

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