FERROMAGNETISM AND A TEMPERATURE-DRIVEN REORIENTATION TRANSITION IN THIN ITINERANT-ELECTRON FILMS

The temperature-driven reorientation transition which, up to now; has been studied by use of Heisenberg-type models only, is investigated wi thin an itinerant-electron model. We consider the Hubbard model for a thin fcc(100)film together with the dipole interaction and a layer-dep endent anisotropy field. The isotropic part of the model is treated by use of a generalization of the spectral:density approach to the film geometry. The magnetic properties of the film are investigated as a fu nction of temperature and film thickness and are analyzed in detail wi th help of the spin- and layer-dependent quasiparticle density of stat es. By calculating the temperature dependence of the second-order anis otropy constants we find that both types of reorientation transitions, from out-of-plane to in-plane (''Fe-type'') and from in-plane to out- of-plane (''Ni-type'') magnetization are possible within our model. In the latter case the inclusion of a positive volume anisotropy is vita l. The reorientation transition is mediated by a strong reduction of t he surface magnetization with respect to the inner layers as a functio n of temperature and is found to depend significantly on the total ban d occupation. [S0163-1829(98)03926-5].