Inhomogeneous surface and volume magnetic states in ferromagnetic films close to the Curie temperature

Abstract

We present a theory of nucleation of one- and two-dimensional lattices of surface and volume domains in ferromagnetic films close to the Curie point in a magnetic field normal to the film surface. A class of uniaxial ferromagnetic films with the ‘easy axis’ perpendicular to the surface is considered. It is shown that in thick ferromagnetic films with a positive surface energy of exchange origin at a temperature exceeding the temperature of the inhomogeneous volume magnetic state nucleation, the paramagnetic phase becomes unstable with respect to the surface domain structure nucleation. The critical value of the surface energy for the surface domain nucleation is found. A phase transition from the surface domain structure to the volume structure is a first-order phase transition. In thin films a set of phase transitions (paramagnetic phase → volume domain structure → paramagnetic phase) is predicted with increasing film thickness. The existence of such a transition is entirely controlled by the surface energy. A phase diagram of the inhomogeneous surface and volume states is constructed and the parameters of the nucleating surface and volume domains are defined. The effect of magnetization fluctuations on the results obtained is discussed.