Direct imaging of magnetic field-driven transitions of skyrmion cluster states in FeGe nanodisks

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 113; no. 18; pp. 4918 - 4923
• Main Authors: Zhao, Xuebing, 赵雪冰, Jin, Chiming, Wang, Chao, Du, Haifeng, Zang, Jiadong, Tian, Mingliang, Che, Renchao, Zhang, Yuheng
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 03-05-2016; National Acad Sciences
• Subjects: Atoms & subatomic particles; Magnetic fields; Nanostructured materials; Phase transitions; Physical Sciences; Thermal energy; Transmission electron microscopy; spintronics; Lorentz TEM; skyrmion; FeGe
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1600197113

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.