Phase Field Simulations of Magnetic Domain Stability in Anisotropic Polycrystals

Scaling effect in finite-size magnetic materials is manifested as a transition of domain structures upon increasing size of the magnet, typically from a flower-like domain structure to a vortex-type multi-domain structure within a magnetic cube with cubic or uniaxial magnetocrystalline anisotropy. In finite-size magnetic bicrystals or polycrystals, the thermal stability of these domain structures is further dependent on the size and orientation of the grains. We explore the stability of these states in ferromagnetic crystals using phenomenological phase-field simulations, using the critical size of a system as a metric of the stability of the magnetic particle. Our system parameters for the simulations included the anisotropy strength, grain size, and grain orientation of the system, all of which contributed to the shape and behavior of the magnetic domain. We find that grain size and anisotropy strength have a relatively weak effect on the stability of the magnetic phase of a polycrystal.