FRONT PROPAGATION IN UNIAXIAL FERROMAGNETS

Abstract

This work is a theoretical study of fronts propagating into an uniaxial ferromagnetic medium with velocity v, when the magnetization, M, is driven by a DC applied magnetic field, H0, from the demagnetized to the magnetized state. It is assumed that the dynamics of M is govern by the Landau–Lifshitz–Gilbert equation (LLGE). We also consider an effective field that includes in-plane uniaxial, HU, and shape anisotropy fields, HD. We show that, in the particular case of uniformly translating profiles, this equation reduces to a damped-forced Duffing's equation, with a family of solutions that describe periodic oscillating (PO), damped oscillating (DO) or exponential front profiles (EF). Of particular interest is the existence of a critical speed, v0, below which there are no stable states for the magnetization. When the velocity of the profile exactly equals v osc , the only stable states are the PO profiles. Above v osc , there is an asymptotic speed, v*, that separates the DO profiles from EF profiles. This velocity (v*) is connected with the existence of a non-linear marginal stability point for front propagation. Both v0 and v* depend on the applied field and on the anisotropy constants of the material. A stability diagram for front propagation and magnetization curves are also calculated.