Advances in research on three-dimensional spin dynamics of magnetic Hopfons driven by current

[ Instrument R & D of instrument network ] Hopfion (hopfion) is a three-dimensional topological soliton. Its topology can be described by Hopfhe (QH). It has a delicate and ingenious magnetic structure, so it is expected to produce novel physical phenomena. Hopfons can exist stably in a variety of physical systems, not only related to cosmic strings, low-energy limit Young-Mills theory, but also related to interesting physical phenomena such as vortex rings and spherical lightning, so the related Research has been widely concerned by people. However, due to the complexity of related models, little is known about the basic physical properties of Hopfson, especially the dynamic properties. Recently, there are theories predicting the existence of stable magnetic Hopfons, so its dynamic properties in magnetic systems can be further studied. The most basic way to drive the motion of the magnetic Hopfton is to apply an electric current and push the movement of the Hopfton through spin transfer torque (STT). Magnetic Hopfson is expected to become another hot topic in the field of topological spintronics after magnetic skyrmion.

Recently, Liu Yizhou, a postdoctoral fellow in the M02 research group of the State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences / Beijing National Research Center for Condensed Matter Physics, researcher Han Xiufeng, collaborated with Professor Zang Jiadong and Dr. Hou Wentao of the University of New Hampshire in the United States, studied the frustration magnet Three-dimensional spin dynamics. Because the Hopfson in the frustrating magnet can exist stably without artificial boundary conditions, its three-dimensional characteristics can be fully demonstrated. The research of this project first focused on the Hopfson with QH = 1, and stimulated its motion through adiabatic and non-adiabatic spin transfer torque. Magnetic Hopfons exhibit rich dynamic responses under current drive, including translation, rotation, and scaling motions that are entangled in phase space. At the same time, its motion pattern is also closely related to the non-adiabatic coefficient of spin transfer torque. The dynamic equations based on the spin Bailey phase and the general form Thiele method can well describe the dynamic process of Hopfson. In addition, the phenomenological description between the Hopfson dynamics and the Scrimson-anti-skrimson pair dynamics also shows the cross-dimensional dynamic relationship between different topological magnetic solitons. Since the method used in this study is based on assembly coordinates rather than the Hamiltonian containing the specific spin interactions of the system, it can also be used to study the general dynamic properties of Hopfons in addition to magnetic systems. At the same time, we can also expect more novel dynamics and transport phenomena to be discovered in the Hopfson with a larger QH. These interesting dynamic processes may be applied to the future of new 3D spintronics materials and device physics Development. The relevant results were published in "Physical Review Letters".

The research was supported by the Ministry of Science and Technology [Project No. 2017YFA0206200], the National Natural Science Foundation of China [Project Fund No. 51831012, 11804380] and the Chinese Academy of Sciences Key Frontier Science Research Program [Project No. QYZDJ-SSW-SLH016].