Microwave resonances of magnetic skyrmions in thin film multilayers

Bhartendu Satywali,Liqing Pan,A P Petrović,Christos Panagopoulos,Shikun He,Markus Garst,Markus Garst,Volodymyr P Kravchuk,Volodymyr P Kravchuk,Volodymyr P Kravchuk,M Raju,Fusheng Ma

doi:10.1038/s41467-021-22220-1

Abstract

Non-collinear magnets exhibit a rich array of dynamic properties at microwave frequencies. They can host nanometre-scale topological textures known as skyrmions, whose spin resonances are expected to be highly sensitive to their local magnetic environment. Here, we report a magnetic resonance study of an [Ir/Fe/Co/Pt] multilayer hosting Néel skyrmions at room temperature. Experiments reveal two distinct resonances of the skyrmion phase during in-plane ac excitation, with frequencies between 6–12 GHz. Complementary micromagnetic simulations indicate that the net magnetic dipole moment rotates counterclockwise (CCW) during both resonances. The magnon probability distribution for the lower-frequency resonance is localised within isolated skyrmions, unlike the higher-frequency mode which principally originates from areas between skyrmions. However, the properties of both modes depend sensitively on the out-of-plane dipolar coupling, which is controlled via the ferromagnetic layer spacing in our heterostructures. The gyrations of stable isolated skyrmions reported in this room temperature study encourage the development of new material platforms and applications based on skyrmion resonances. Moreover, our material architecture enables the resonance spectra to be tuned, thus extending the functionality of such applications over a broadband frequency range.

Highlights

Non-collinear magnets exhibit a rich array of dynamic properties at microwave frequencies
In contrast with magnetic skyrmion arrays in bulk single crystals, Néel skyrmions at ferromagnet–heavy-metal (FM-HM) interfaces are stabilised by the interfacial Dzyaloshinskii–Moriya interaction
Our micromagnetic simulations indicate that the lowfrequency (LF) mode is associated with a CCW gyration of the skyrmion core, while the CCW precession of the magnetisation within the inter-skyrmion zones is the predominant contributor to the high-frequency (HF) mode

Summary

Introduction

Non-collinear magnets exhibit a rich array of dynamic properties at microwave frequencies They can host nanometre-scale topological textures known as skyrmions, whose spin resonances are expected to be highly sensitive to their local magnetic environment. In contrast with magnetic skyrmion arrays in bulk single crystals, Néel skyrmions at ferromagnet–heavy-metal (FM-HM) interfaces are stabilised by the interfacial Dzyaloshinskii–Moriya interaction Their configuration can range from dilute to dense disordered arrays, as well as ordered lattices. Magnetic multilayers are promising candidates for developing skyrmion-based technologies, since they combine skyrmion stability at room temperature with the ability to finely tune their magnetic parameters via the multilayer geometry The latter significantly amplifies the role of the dipole–dipole interaction, enriching the properties of skyrmion phases. The third mode emerges at high fields and is associated with the uniform precession of the field-polarised magnetisation

Methods

Results

Conclusion