Influence of Magnetic External Field and Particle Size on the Formation of a Single Domain State

Magnetic particles are widely employed in applications ranging from medical to industrial. Their magnetic state, a single-domain versus a multi-domain configuration, depends on their size as well as the strength and frequency of an applied magnetic field. The critical size of a single-domain ferromagnetic/ferrimagnetic particle can be determined by minimizing the total free energy, which should include the Zeeman energy term when an external field is applied. To study the effect of an applied field on the critical size of single-domain particles as a function of their size, we performed numerical simulations using MuMax3 software for Fe, Co, Fe3O4, MgZn ferrites, and BaFe12O19. These materials exhibit a wide range of values for magnetic properties such as saturation magnetization and anisotropy. We determined the critical field at which a given sized particle becomes a single-domain magnetic particle. Our MuMax3 calculations for an iron spherical particle were compared with Kondorskii's analytical theory.