Stabilization of ferromagnetic order in epitaxial ultrathin Fe films

Epitaxial Fe(001) films with thicknesses less than 20 monolayers were grown on epitaxial Au(001) surfaces by molecular beam epitaxy. All films have a fourfold anisotropy and a negligible uniaxial component. In contrast, the magnetic behavior of Fe films on GaAs(001) is governed by a superposition of a dominating uniaxial and a fourfold anisotropy component. The temperature dependence of the spontaneous magnetization MS for T < 0.5T(C) can be well described by Bloch's T(3/2) law for both systems. With decreasing film thickness the spin wave parameter B increases significantly compared to the bulk in both cases. However, for the same thickness B is reduced in Fe/GaAs(001) compared to Fe/Au(001) films. This is attributed to the presence of the strong uniaxial anisotropy in Fe/GaAs(001) which apparently stabilizes the ferromagnetic order against thermal excitations. (c) 2005 American Institute of Physics.