Group Seminar 2019/20

New skyrmion resonance modes in a chiral magnetic insulator

1. Aqeel, J. Sahliger, T. Taniguchi, D. Mettus, A. Bauer, C. Pfleiderer, C.H. Back

Physik Department, Technische Universität München, Garching, Germany

In addition to the high temperature skyrmion pocket [1], a new independent low-temperature skyrmion (LTS) phase has recently been discovered in the chiral magnetic insulator Cu₂OSeO₃ [2]. Unlike the high temperature skyrmion phase, the LTS phase has a different stabilization mechanism; it is proposed that the skyrmion lattice is stabilized by the cubic anisotropy contribution [2,3] and not by fluctuations. One interesting question is, how a different stabilization mechanism influences the magnetization dynamics and how it modifies the magnetic resonance response of the skyrmion lattice. Using a broadband spin-wave spectroscopy technique, we systematically track the magnetic resonance response in different magnetic phases of Cu₂OSeO₃, focusing on the LTS phase around 5K. We identify distinct resonances associated with the newly discovered tilted conical and LTS phases of Cu₂OSeO₃. We observe a strong dependence of these modes on static magnetic field history. The spectral weights of the skyrmion resonance modes increase when cycling the magnetic field within this phase. The magnetic phase boundaries and the effect of field cycling on the population agrees well with our magnetometery measurements. To understand the observed resonance spectra, we use a phenomenological model based on previous work [4], but adding cubic anisotropy contributions. Our theoretical model confirms that the cubic anisotropy contribution is the key ingredient for the observed resonance spectra. Moreover, theoretical modeling provides evidence that the hybridization mechanism of different resonance modes is solely provided by the cubic anisotropy.

[1] S. Seki, et al., Science 336, 198 (2012).

[2] A. Chacon, et al., Nature Physics 14, 936 (2018).

[3] M. Halder, et al., Physical Review B 98, 144429 (2018).

[4] T. Schwarze, Nature Materials 14, 478 (2015).