Magnetism and overlayer-induced reorientation of magnetization in thin itinerant-electron films

The magnetic properties and overlayer-induced reorientation of magnetization in thin ferromagnetic films are investigated within the single-band Hubbard model. A generalization of modified alloy analogy (MAA) is applied to deal with modifications due to the reduced translational symmetry. Within the MAA the actual type of alloy analogy is determined self-consistently. The MAA allows, in particular, the investigation of quasiparticle lifetime effects in the paramagnetic as well as the ferromagnetic phase. The layer magnetizations are calculated as a function of temperature and film thickness and are microscopically analyzed in detail with help of the spin- and layer-dependent quasiparticle density of states. By calculating the overlayers dependence of the second-order anisotropy constants, we find that very thin overlayers can induce a reorientation of magnetization from in-plane to out-of-plane directions, however, thick overlayers rotate the magnetization from out-of-plane to in-plane directions again. In addition, the temperature and thickness induced reorientation of magnetization can also be understood in our theory.