In-situ Brillouin light scattering study of the thickness dependence of the magnetic anisotropy in uncovered and Cu-covered Fe/GaAs(100) ultrathin films

The dynamical magnetic properties of ultrathin Fe/GaAs~001! films in the thickness range 5-100 Å have been studied by in situ Brillouin light scattering. Measurement of the spin-wave frequency as a function of both the intensity and the in-plane direction of the applied magnetic field, as well as of the incidence angle of light, enabled us to determine the magnetic parameters of the films. A continuous evolution from uniaxial to biaxial in-plane magnetic anisotropy has been observed with increasing thickness, together with a marked increase of the effective magnetization. Remarkably, we also found that the presence of a Cu capping layer, even 1 ML thick, completely suppresses the uniaxial anisotropy in the thinnest samples. This effect is discussed in terms of the possible underlying physical mechanisms.