Multiple stable Bloch points in confined helimagnetic nanostructures*

It was predicted by Beg et al. [1] that a stable Bloch point (BP) exists at the interface of two nano-disks with Dzyaloshinskii-Moriya-interaction of opposite chirality in the absence of an external magnetic field. Two different configurations, head-to-head and tail-to-tail, were discovered and switching between them was demonstrated by using an external magnetic field. The two co-existing distinct stable configurations make BPs a possible candidate for future memory devices. Mandatory for any application is finding multiple BPs in a single sample.
In this work, we show using micromagnetic simulations that a nano-strip consisting of two layers with opposite chirality (opposite sign of D) can host multiple BPs. We simulate strips with various lengths l and widths w and relax multiple initial configurations for each (l, w) pair. We obtain a (l, w) parameter-space-diagram showing the meta-stable configurations. We find geometries hosting multiple BPs of the same or alternating opposite character. Our findings contribute to both possible application and theoretical understanding.

[1] Beg, M. et al. Scientific Reports 9, 7959 (2019).