Microwave resonances of magnetic skyrmions in thin film multilayers

TL;DR

This study investigates microwave resonances of Nel skyrmions in [Ir/Fe/Co/Pt] multilayers at room temperature, revealing two distinct resonant modes sensitive to magnetic environment and tunable via layer spacing, with implications for skyrmion-based applications.

Contribution

First experimental demonstration of room-temperature skyrmion resonances in multilayers, showing tunability and detailed mode localization through micromagnetic simulations.

Findings

Two distinct skyrmion resonances observed at 6-12 GHz.

Resonance properties depend on out-of-plane dipolar coupling.

Resonance spectra can be tuned via layer spacing.

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 N\'eel 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.