title: Direct imaging of magnetic field-driven transitions of skyrmion cluster states in FeGe nanodisks.
abstract: Magnetic skyrmion is a nanosized magnetic whirl with nontrivial topology, which is highly relevant for applications on future memory devices. To enable the applications, theoretical efforts have been made to understand the dynamics of individual skyrmions in magnetic nanostructures. However, directly imaging the evolution of highly geometrically confined individual skyrmions is challenging. Here, we report the magnetic field-driven dynamics of individual skyrmions in FeGe nanodisks with diameters on the order of several skyrmion sizes by using Lorentz transmission electron microscopy. In contrast to the conventional skyrmion lattice in bulk, a series of skyrmion cluster states with different geometrical configurations and the field-driven cascading phase transitions are identified at temperatures far below the magnetic transition temperature. Furthermore, a dynamics, namely the intermittent jumps between the neighboring skyrmion cluster states, is found at elevated temperatures, at which the thermal energy competes with the energy barrier between the skyrmion cluster states.
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai 200438, China;
authors.forename: Xuebing
authors.initials: X
authors.lastname: Zhao
authors.affiliation: High Magnetic Field Laboratory, Chinese Academy of Science, Hefei 230031, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;
authors.forename: Chiming
authors.initials: C
authors.lastname: Jin
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai 200438, China;
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: High Magnetic Field Laboratory, Chinese Academy of Science, Hefei 230031, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;
authors.forename: Haifeng
authors.initials: H
authors.lastname: Du
authors.affiliation: Department of Physics and Materials Science Program, University of New Hampshire, Durham, NH 03824.
authors.forename: Jiadong
authors.initials: J
authors.lastname: Zang
authors.affiliation: High Magnetic Field Laboratory, Chinese Academy of Science, Hefei 230031, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China; tianml@hmfl.ac.cn rcche@fudan.edu.cn.
authors.forename: Mingliang
authors.initials: M
authors.lastname: Tian
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai 200438, China; tianml@hmfl.ac.cn rcche@fudan.edu.cn.
authors.forename: Renchao
authors.initials: R
authors.lastname: Che
authors.affiliation: High Magnetic Field Laboratory, Chinese Academy of Science, Hefei 230031, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;
authors.forename: Yuheng
authors.initials: Y
authors.lastname: Zhang
keywords: FeGe; Lorentz TEM; skyrmion; spintronics