Simulating Bloch Points Using Micromagnetic and Heisenberg Models

Magnetic Bloch points (BPs) are highly confined magnetization configurations, which often occur in transient spin dynamics processes. However, opposing chiralities of adjacent layers, for instance, in a FeGe bilayer stack, can stabilize such magnetic BPs at the layer interface. These BP configurations are metastable and consist of two coupled vortices (one in each layer) with the same circulation and opposite polarization. Each vortex is stabilized by opposite sign Dzyaloshinskii-Moriya interactions (DMIs). An open question, from a methodological point of view, is whether the Heisenberg (HB) model approach (atomistic model) is to be used to study such systems or if the computationally more efficient micromagnetic (MM) models can be used and still obtain robust results. We are modeling and comparing the energetics and dynamics of a stable BP obtained using both HB and MM approaches. We find that an MM description of a stable BP leads qualitatively to the same results as the HB description and that an appropriate mesh discretization plays a more important role than the chosen model. Furthermore, we study the dynamics by shifting the BP with an applied in-plane (IP) field and investigating the relaxation after switching the field off abruptly. The precessional motion of coupled vortices in a BP state can be drastically reduced compared to a classical vortex (CV), which may also be an interesting feature for fast and efficient devices. A recent study has shown that a bilayer stack hosting BPs can be used to store information.