MAGNETIZATION REVERSAL IN SPHERICAL-PARTICLES

Bifurcation analysis has been applied to nucleation of magnetization reversal by curling1 in spherical particles. Nucleation is a pitchfork bifurcation, with the external magnetic field as control parameter. Curling occurs as a local minimum of the energy when it exists as a solution of Brown's nonlinear equation2 for external field in excess of the critical value for curling. The existence of such a solution can be determined from second-order perturbation theory. When it exists, the magnetization varies continuously as the external field exceeds the critical value; otherwise, it must suffer a discontinuity. We have computed the solutions to Brown's equation to second order near nucleation. The transition is always a continuous one when the anisotropy constant K is not sufficiently large.