Multistability and skyrmion annihilation mechanisms in nanodots near ordering temperature

Abstract Magnetic skyrmions are promising candidates for next-generation information carriers. In confined geometries, they often coexist with other (meta)stable magnetic states under identical conditions, enabling skyrmion-based multi-bit storage applications. Advancing these applications requires a comprehensive understanding of multistability and skyrmion annihilation mechanisms. Here, we employ an iterative method to identify the minima and saddle points on the energy surface of nanodots under varying magnetic fields and uniaxial anisotropies. We find that easy-axis uniaxial anisotropy favors discontinuous transitions, leading to multiple multistability regions within the phase diagram. In particular, a quadrastability region—featuring the coexistence of a skyrmion, a quasi-uniform state, and their oppositely magnetized counterparts—emerges near zero field. In these multistability regions, we identify various saddle points that vanish through distinct mechanisms. Using the nudged elastic band method, we further reveal skyrmion annihilation pathways linked to these saddle points. These findings provide crucial insights for developing skyrmion-based multi-bit memory devices.