Band Model of Ferromagnetic Thin Films

Spontaneous magnetization of ferromagnetic thin films in the band model is calculated in a manner analogous to that used for bulk bodies. The thin film is considered as a superposition of monoatomic layers. To calculate the mean values of the numbers of electrons with oriented spins as traces of the electronic density matrix in Bloch representation the electron‐energy spectrum is obtained. The assumptions made are that the periodicity conditions are satisfied in the plane of a layer and that the lack of a part of nearest neighbors for the boundary layers is taken into account in the direction perpendicular to the surface. The Fermi level is found in the same way. The behavior of the Curie temperature with the decrease of the film thickness is in a better accord with the experimental data than that obtained in the band theory but by means of another procedure. The important role of the surface states in the results obtained is shown. The spin‐wave energy spectrum is discussed.