Fully-Vector Simulation Framework for the Investigation of Magnetisation Dynamics and Skyrmions

Abstract

Atomistic simulations play a huge part in our understanding of static and dynamic magnetic states in current state-of-the-art research. Motivated by the recent interest in magnetic Heusler alloys, a model based on the LLG equation was developed for investigating magnetisation dynamics in near-compensated ferrimagnets. These materials, including Mn2RuxGa (MRG), are predicted and often experimentally verified to possess key properties, including THz resonance frequencies and high spin-polarisation at the Fermi level [1, 2]. Another hot topic of study are magnetic skyrmions, topological defects in the spin texture of non-centrosymmetric crystals with chiral interactions. There is much interest in the dynamics of skyrmions, with fast skyrmionic magnetic storage one potential application [3, 4]. In this work, the stability of skyrmion states in a 1D ferrimagnet was investigated as a function of material parameters such as anisotropy and Dzyaloshinskii-Moriya interaction (DMI), see Fig. 1. Additionally, skyrmion propagation speed and breathing mode frequency [5] are investigated under the influence of an external magnetic field and/or spin-polarised current. The model has also been applied as a computationally efficient method to obtain magnon frequency dispersions. By applying a perturbing field pulse and taking the Fourier Transform of the resulting dynamics, the entire magnon dispersion can be obtained. A simple example for a 1D ferrimagnetic chain with Heisenberg exchange, DMI and uniaxial anisotropy is shown in Fig. 2. MRG shows compensation of its ferrimagnetic moment at room temperature and as a result is predicted to support sustained spin oscillations in the THz region [6]. Our simple model, once adjusted to accommodate the symmetry and dimensionality of the real material, will represent an efficient method to theoretically investigate the existence of such oscillations and of potential chiral ground states.