Growth of ultrathin Fe films on Ge(100): Structure and magnetic properties

The structure and magnetic properties of ultrathin Fe films grown on Ge(100) at room temperature have been studied by low-energy electron diffraction, Auger electron spectroscopy (AES), angle-resolved AES, and in situ magneto-optical Ken effect (MOKE) measurements. Fe initially grows on Ge(100) in a disordered fashion, with local order commencing around 4 ML. The film grows with a bcc structure for thicknesses greater than 7 ML. Our data are consistent with 6% Ge intermixed in the films. Significant intermixing starts at about 160 degrees C, with rapid diffusion of Fe into the bulk occurring at temperatures higher than 400 degrees C. A single-loop to stepped-loop to single-loop sequence of ferromagnetic loops was observed by MOKE measurements. Hysteresis loop simulations were performed based on the coherent model, the results suggesting that strong in-plane uniaxial anisotropy exists in these films, especially for very thin films. The sequence of loops is due to the increase of the ratio between the cubic anisotropy and the uniaxial anisotropy as the film thickness increases.