The temperature dependence of magnetic anisotropy in ultra-thin films

Results for the reorientation of the magnetization in 7.6 ML Ni(001)/Cu(001) as a function of temperature T are presented. The magnetocrystalline anisotropy coefficients up to fourth order are determined by in situ UHV ferromagnetic resonance. The angle theta(eq) of the spontaneous magnetization measured from the film normal is found to change continuously from 90 degrees at 200 K, i.e. in-plane, to 16 degrees at 250 K, to 0 degrees above 300 K. The unique reorientation of the magnetization to a perpendicular direction above a critical temperature T-R is described quantitatively by the temperature dependence of the volume and interface anisotropy contributions K-2(V) and K-2(S) which were also measured. This is compared with the case of Gd(0001)/W(110) and Ni(111)/W(110). One finds that there is no universal behavior for the temperature dependence of K-2(V) and K-2(S) the case of Ni, the behavior of K-2(V) is well described by a magnetoelastic model which uses only the temperature dependence of the elastic and magnetostrictive constants of bulk Ni and the lattice mismatch to the substrate.