In-situ GHz Dynamics of Skyrmions Probed with SANS

Abstract

Magnetic skyrmions present interesting and unique pseudo-particle behaviors which arises from their topological protection [1-2]. Key among these behaviors is their resonant dynamics, under microwave fields, which include both breathing and gyration modes. Due to their small size, and magnetic-only contrast of skyrmions, coupled with high frequency dynamics – in the GHz regime – it is challenging to do in-situ measurements on these excitations. This work reports the use of small angle neutron scattering (SANS) to capture the dynamics of hybrid skyrmions stabilized in Fe/Gd multilayers by means of dipolar interactions. Using perpendicular DC fields and in-plane RF fields, we explored the gyration modes of hybrid skyrmions away, below, at, and above resonance [Fig.1(a-d)]. We find the dynamic modes of hybrid skyrmions contribute to the SANS signal in two ways: first, the scattered neutrons incur additional transverse momentum as a result of scattering from a moving source, and second, the gyration skyrmions disrupt ordering of the lattice giving rise to enhancement form-factor scattering. Ferromagnetic resonance measurements confirm the RF and DC field conditions for these gyration modes. Our results offer new insights into the nanoscale dynamics of magnetic skyrmions and present a unique use of SANS to probe magnetization dynamics.  Fig.1 2D SANS pattern of magnetic skyrmions under different magnetic fields and excitation frequencies: (a) Static state (H=0, RF=0), (b) below-resonance state (H=150 mT, RF=1.2 GHz), (c) at-resonance state (H=150 mT, RF=1.3 GHz) and (d) above-resonance state (H=150 mT, RF=1.4 GHz). All 2D images are plotted with the same intensity scale.