Magnetic anisotropies and nature of the spin-reorientation transition in thin Ni/Cu(001) films

Abstract It was shown experimentally for a variety of systems that the anisotropy characterizing the thin films is extremely sensitive to lattice geometry and film thickness as well as type of substrate. We consider the spin reorientation transition (SRT) in a ferromagnetic Heisenberg system Ni/Cu(0 0 1) with different kind of magnetic anisotropies as a function of temperature and Ni film thickness. The Heisenberg type Hamiltonian describing the Ni/Cu(0 0 1) system assumes the magnetization vector to process around the surface normal and its direction is completely determined by two angles of rotation: polar and azimuth. We use the thermodynamic approach to the problem, which is, in general, based on the free-energy functional construction determined by means of internal energy and entropy calculations. The equilibrium values of all parameters characterizing the magnetic properties of the system are obtained by minimizing free energy with respect to these parameters. The sensitivity of the SRT on exchange anisotropy, shape anisotropy and uniaxial anisotropy parameters is then analyzed in details. It is shown that the direction of magnetization is determined by the competition between uniaxial and shape anisotropy. The use of the Valenta model for the thin film description allows us to present the SRT phenomenon in the layer resolved mode. It is shown that interplay between anisotropies can induce non-collinear spin structure in thin magnetic films.