Calculation of the size dependence of the coercive force in fine particles

A numerical micromagnetic model is employed to calculate the energy barrier for the reversal in a γFe₂O₃ particle of cubic shape. The model simulates magnetization reversal by coherent rotation and curling. It simulates the thermal fluctuations of the magnetization by a method or parametric optimization and gives the dependence of the coercive force on particle size. The size dependence of the switching field is a good qualitative fit to experimental data. A small reduction in the superparamagnetic size of γFe₂O ₃ particles is attributed to the surface imperfection. The flower magnetization configuration appears to be metastable over an intermediate size region, and a spontaneous transition to a vortex state of lower energy is expected at normal temperatures