INHOMOGENEOUS SURFACE AND VOLUME MAGNETIC STATES IN FERROMAGNETIC-FILMS CLOSE TO THE CURIE-TEMPERATURE

We present a theory of nucleation of one- and two-dimensional lattices of surface and volume domains in ferromagnetic films close to the Cur ie point in a magnetic field normal to the film surface. A class of un iaxial ferromagnetic films with the 'easy axis' perpendicular to the s urface is considered. It is shown that in thick ferromagnetic films wi th a positive surface energy of exchange origin at a temperature excee ding the temperature of the inhomogeneous volume magnetic state nuclea tion, the paramagnetic phase becomes unstable with respect to the surf ace domain structure nucleation. The critical value of the surface ene rgy for the surface domain nucleation is found. A phase transition fro m the surface domain structure to the volume structure is a first-orde r phase transition. In thin films a set of phase transitions (paramagn etic phase --> volume domain structure --> paramagnetic phase) is pred icted with increasing film thickness. The existence of such a transiti on is entirely controlled by the surface energy. A phase diagram of th e inhomogeneous surface and volume states is constructed and the param eters of the nucleating surface and volume domains are defined. The ef fect of magnetization fluctuations on the results obtained is discusse d.