Perpendicular and in-plane magnetic anisotropy in epitaxial Cu/Ni/Cu/Si(111) ultrathin films

Epitaxial ultrathin Cu/Ni/Cu films with Ni thickness in the range 1.5-6 nm have been grown by UHV evaporation on the Si(111)-737 surface. In situ characterization made by low-energy electron diffraction and Kikuchi electron diffraction revealed that both Ni and Cu films grow epitaxially on Si, with a ~111! orientation and with their ~1 ¯ 10! axis parallel to the ~12¯1! axis of the Si substrate. Magneto-optical Kerr effect measurements performed at room temperature have shown that the preferential direction of magnetization lies in the film plane for Ni thickness above 3 nm, while it is perpendicular to the film plane for lower thickness. Brillouin light scattering was then exploited to study the spin-wave dispersion as a function of both the applied magnetic field and the wave vector direction on the surface plane. In order to interpret the Brillouin data, we have used a macroscopic model which takes into account both dipolar and exchange interactions, as well as bulk and interface anisotropy for the ~111! plane of a cubic crystal. This enabled us to determine, in addition to the other magnetic parameters, both the in-plane and the out-of-plane anisotropy constants. The observed dependence of these constants on the film thickness indicates that the magnetic anisotropy is mainly of magnetoelastic origin.