High-density, spontaneous magnetic biskyrmions induced by negative thermal expansion in ferrimagnets.

Song, Yuzhu; Xu, Tiankuo; Zhao, Guoping; Xu, Yuanji; Zhong, Zhicheng; Zheng, Xinqi; Shi, Naike; Zhou, Chang et al. · Sci Adv · 2023

basic_science · Level V

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Abstract

Magnetic skyrmions are topologically protected quasiparticles that are promising for applications in spintronics. However, the low stability of most magnetic skyrmions leads to either a narrow temperature range in which they can exist, a low density of skyrmions, or the need for an external magnetic field, which greatly limits their wide application. In this study, high-density, spontaneous magnetic biskyrmions existing within a wide temperature range and without the need for a magnetic field were formed in ferrimagnets owing to the existence of a negative thermal expansion of the lattice. Moreover, a strong connection between the atomic-scale ferrimagnetic structure and nanoscale magnetic domains in Ho(Co,Fe)<sub>3</sub> was revealed via in situ neutron powder diffraction and Lorentz transmission electron microscopy measurements. The critical role of the negative thermal expansion in generating biskyrmions in HoCo<sub>3</sub> based on the magnetoelastic coupling effect is further demonstrated by comparing the behavior of HoCo<sub>2.8</sub>Fe<sub>0.2</sub> with a positive thermal expansion.