ATOMIC STRUCTURE AND MAGNETIC ANISOTROPY IN ULTRATHIN Fe FILMS ON Au(001)

We have investigated the growth and magnetic properties of ultrathin Fe films on Au(001). The films used for magnetometry have been prepared by MBE on pre-annealed MgO(001) single crystals. Epitaxial growth of the 300-500 monolayer Au buffer layer as well as of the Fe films in the monolayer range could be achieved by use of a Cr seed layer. Epitaxial quality and surface structure was controlled in situ by electron diffraction (LEED, RHEED) and ex situ by STM and AFM. Comparative growth studies were performed for Fe-films on a Au single crystal substrate by in situ STM and ion scattering spectroscopy. We have investigated the magnetic anisotropy of Fe films in the range 3-50 monolayers with alternating gradient magnetometry (AGM). We find a uniaxial out-of-plane contribution of the surface anisotropy which promotes a spontaneous out-of-plane magnetization for films < 2.1 monolayers. Additionally, we report on a fourfold in-plane surface anisotropy, which leads to a switching of the in-plane easy axes into the [110] and [-110] directions for the 3 and 5 monolayer Fe films. We discuss these anisotropy phenomena in context with the breaking of translational symmetry at the interface.