Recently, Associate Professor Hou Yusheng's research group at the School of Physics, Sun Yat-sen University, in collaboration with Professor Ruqian Wu from the Department of Physics and Astronomy at the University of California, Irvine, has made significant progress in the study of magnetic skyrmions. They have, for the first time internationally, proposed the use of the controllability of magnetic anisotropy to regulate the transition between the intrinsic magnetic skyrmion state and the ferromagnetic state, thereby achieving control over the generation and annihilation of magnetic skyrmions. The related findings have been published in the form of a cover article in "Nano Letters."
Magnetic skyrmions are topologically protected quasi-particles with a vortex magnetic structure, known for their ease of manipulation, small size, and fast driving speed. Therefore, spintronic devices based on magnetic skyrmions are expected to meet the performance requirements of future devices for high capacity, high speed, and low power consumption. As a result, magnetic skyrmions are considered the ideal information carrier for future spintronic storage and logic devices. However, the precise generation and annihilation of magnetic skyrmions remain a key challenge in their practical device applications.
Addressing the scientific issue mentioned above, Professor Hou Yusheng's research group conducted first-principles calculations and found that a magnetic field can induce the appearance of magnetic skyrmions in CrYX (Y = S, Se, Te; X = Cl, Br, I) monolayer Janus magnetic materials based on the intrinsic Dzyaloshinskii-Moriya interaction. Building on this, they proposed a scheme to control magnetic skyrmions in two-dimensional van der Waals heterostructures considering the non-volatile polarization properties of two-dimensional ferroelectric materials. After two years of exploratory research, they discovered the transition between the intrinsic magnetic skyrmion state and the ferromagnetic state in a two-dimensional van der Waals heterostructure composed of CrSeI and In2Te3.
In this work, when the polarization of In2Te3 is upward, CrSeI/In2Te3 exhibits a ferromagnetic state with a Curie temperature of 248 K; when the polarization of In2Te3 is flipped downward, its magnetic ground state transitions to a Neel-type magnetic skyrmion state. Further investigations revealed that this transition is induced by the controllable magnetic anisotropy resulting from the direction of the ferroelectric polarization. By studying the effects of temperature and external magnetic fields, they found that the magnetic skyrmions in CrSeI/In2Te3 exhibit strong robustness and can stably exist at 156 K and 0.5 T. Particularly, under an applied external magnetic field of 0.5 T, the radius of the magnetic skyrmions decreases from 8.7 nanometers without an external field to 2.7 nanometers, laying the foundation for miniaturizing magnetic skyrmion devices.
To reveal the universal laws governing the generation of magnetic skyrmions in two-dimensional van der Waals ferromagnetic heterostructures, they defined dimensionless descriptors combining the exchange stiffness coefficient A related to the Heisenberg exchange interaction, the coefficient d related to the Dzyaloshinskii-Moriya interaction, and the effective out-of-plane magnetic anisotropy related to the magnetic anisotropy. Through in-depth analysis, they found that in CrSeI/In2Te3, magnetic skyrmions exist in the system as long as the ferroelectric polarization ranges from 0.69 to 0.98, regardless of whether it is upward or downward.
"Based on the above findings, we have, for the first time internationally, proposed controlling the generation and annihilation of magnetic skyrmions by manipulating magnetic anisotropy and provided descriptors conducive to finding magnetic skyrmions in two-dimensional multiferroic heterostructures, offering valuable theoretical guidance for the design of spintronic devices based on magnetic skyrmions in the future," said the corresponding author of the paper, Hou Yusheng.
Related paper information: https://doi.org/10.1021/acs.nanolett.3c05024
