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

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  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.