Magnetization processes in ferromagnetic cubes

Abstract

A cubic discretization procedure of the micromagnetic energy functional is used to carry out numerical studies of the magnetization process in ferromagnetic cubes. Equilibrium magnetization configurations and their switching behavior are calculated for particle sizes in the range from 100 to 550 Å. In the model calculations the particles are assumed to have uniaxial crystalline anisotropy with an anisotropy constant of 18 500 erg/cm3, a saturation magnetization of 370 emu/cm3, and an exchange constant of 10−6 erg/cm. For particle sizes smaller than 520 Å the remanent state has a flowerlike magnetization configuration. Beyond 520 Å this state is replaced by a vortex structure about the easy axis. For particles smaller than 450 Å switching occurs by approximately uniform rotation of the flower state. The switching fields are larger than the corresponding Stoner–Wohlfarth value. Beyond 450 Å the application of an external field leads to the formation of a vortex configuration. The switching of the vortex configuration involves rotation of the vortex axis at a reduced value of the switching field. The angular dependence of the coercive field is calculated for particle sizes of 200, 400, and 550 Å.