Micromagnetic simulation of magnetization reversal processes in ferromagneticcubes from quasisaturation state

Abstract

Recent divergence in analysing the magnetization processes in isolated particlesbetween analytical micromagnetics and numerical micromagnetics has focused onwhether it is necessary to use nucleation theory in the analysis. Completesaturation is the necessary condition for using nucleation theory. A ferromagneticelliptical particle can be uniformly magnetized in a large field. As the fielddecreases, there exists a nucleation field at which the magnetization deviatesfrom uniform magnetization. On the contrary, a ferromagnetic cube cannever be saturatedly magnetized in any finite homogeneous field. It isdifficult to apply the theory of a nucleation field of an elliptical particleto a cubic particle. One practical way to discuss the ‘nucleation’ in acubic particle is to supervise the magnetization changes from a positivequasisaturation state to a negative quasisaturation state, and find what kind ofreversal modes appear. In this paper, a three-dimensional micromagneticsmodel is implemented to analyse the magnetization reversal processes incubic particles at a field (1.1 × 106 Oe) where the quasisaturation is welldeveloped in a cubic particle. The sizes of particles vary from 400–1000 Å. Afine mesh with 10 × 10 × 10 and a small decreasing step of applied field10 Oe are used in the calculations. The ‘nucleation’ in a cubic particlestarts from the quasiquantization state (flower state). For a particle whosesize is smaller than 1000 Å, the equilibrium magnetization states duringmagnetization reversal processes are a flower state and an anti-flower state, and acoherent rotation happens when the magnetization state changes from aflower state to an anti-flower state. For a larger particle with a size of1000 Å, there exist rather complicated equilibrium magnetization states i.e.a flower state, anticlockwise vortex state, intermediate state, clockwisevortex state, and anti-flower state all appear during the reversal processes.