Geometry induced phase transitions in magnetic spherical shell

TL;DR

This paper investigates how the competition between exchange and magnetostatic interactions induces phase transitions between vortex and onion magnetization states in spherical shells, supported by analytical and simulation results.

Contribution

It provides a detailed analytical phase diagram of magnetization states in spherical shells, revealing a continuous phase transition driven by geometry and interactions.

Findings

Identifies a second-order phase transition between vortex and onion states.

Analytical phase diagram matches micromagnetic simulation results.

Shows the role of geometry and interactions in state stability.

Abstract

Equilibrium magnetization states in thin spherical shells of a magnetically soft ferromagnet are determined by the competition between two interactions: (i) The local exchange interaction favours the more homogeneous onion state with magnetization oriented in meridian directions; such a state is realized in relatively small particles. (ii) The nonlocal magnetostatic interaction prefers the double-vortex configuration with the magnetization oriented in the parallels directions, since it minimizes the volume magnetostatic charges. These sates are topologically equivalent, in contrast to the same-name states of magnetic nanoring. As a consequence, a continuous (the second order) phase transition between the vortex and onion states takes place. The detailed analytical description of the phase diagram is well confirmed by micromagnetic simulations.