Micromagnetic simulation of magnetization reversal processes in ferromagnetic cubes from quasisaturation state

Recent divergence in analysing the magnetization processes in isolated particles between analytical micromagnetics and numerical micromagnetics has focused on whether it is necessary to use nucleation theory in the analysis. Complete saturation is the necessary condition for using nucleation theory. A ferromagnetic elliptical particle can be uniformly magnetized in a large field, As the field decreases, there exists a nucleation field at which the magnetization deviates from uniform magnetization. On the contrary, a ferromagnetic cube can never be saturatedly magnetized in any finite homogeneous field. It is difficult to apply the theory of a nucleation field of an elliptical particle to a cubic particle. One practical way to discuss the 'nucleation' in a cubic particle is to supervise the magnetization changes from a positive quasisaturation state to a negative quasisaturation state, and find what kind of reversal modes appear. In this paper, a three-dimensional micromagnetics model is implemented to analyse the magnetization reversal processes in cubic particles at a field (1.1 x 10(6) Oe) where the quasisaturation is well developed in a cubic particle. The sizes of particles vary from 400-1000 Angstrom. A fine mesh with 10 x 10 x 10 and a small decreasing step of applied field 10 Oe are used in the calculations. The 'nucleation' in a cubic particle starts from the quasiquantization state (flower state). For a particle whose size is smaller than 1000 Angstrom, the equilibrium magnetization states during magnetization reversal processes are a flower state and an anti-flower state, and a coherent rotation happens when the magnetization state changes from a flower state to an anti-flower state. For a larger particle with a size of 1000 Angstrom, there exist rather complicated equilibrium magnetization states i.e. a flower state, anticlockwise vortex state, intermediate state, clockwise vortex state, and anti-flower state all appear during the reversal processes.