Skyrmion Breathing Modes in Synthetic Ferri- and Antiferromagnets

Abstract

Magnetic multilayers can combine strong spin-orbit interaction with lacking inversion symmetry, which may give rise to the presence of topologically nontrivial spin textures, so-called magnetic skyrmions. Recent studies have indicated strongly enhanced propagation velocities of skyrmions in antiferromagnets and compensated ferrimagnets [1]. At the same time, it is unclear how magnetic compensation may affect dynamic excitations of magnetic skyrmions, such as breathing modes, which entail an oscillation of the skyrmion size at GHz frequencies [2]. Here, we present comprehensive micromagnetic simulations of these resonance modes in synthetic ferri- and antiferromagnets that are excited by either out-of-plane radiofrequency magnetic fields or spin torques. The observed features in the calculated power spectra exhibit a systematic dependence on the strength of the RKKY-like antiferromagnetic coupling between the individual magnetic layers and are related to pure in-phase and anti-phase breathing modes as well as to hybridizations of breathing and spin wave modes that are characteristic for the considered circular-shaped geometry [3]. As a simplified classical analog, the coupled skyrmion breathing modes can be viewed as two harmonic oscillators that are connected by a spring. The experimental detection of these resonant oscillation modes may provide a means for skyrmion sensing applications and for the general characterization of skyrmion states in multilayer stacks with antiferromagnetic interlayer exchange coupling. This work is supported by the Deutsche Forschungsgemeinschaft (DFG) through the research fellowship LO 2584/1-1.