REORIENTATION TRANSITION OF ULTRATHIN FERROMAGNETIC-FILMS

We demonstrate that the reorientation transition from out-of-plane to in-plane magnetization with decreasing temperature as observed experim entally in Ni films on Cu(001) can be explained on a microscopic basis . Using a combination of mean-field theory and perturbation theory, we derive an analytic expression for the temperature-dependent anisotrop y. The reduced magnetization in the film surface at finite temperature s plays a crucial role for this transition as with increasing temperat ure the influence of the uniaxial anisotropies is reduced at the surfa ce and is enhanced inside the film.