The Effect of Postgrowth Oxygen Exposure on the Magnetic Properties of Ni on the Cu-CuO Stripe Phase

Full text: The magnetism and morphology of thin Ni films deposited on clean and oxygen covered Cu(110) has been studied. In the latter case oxygen acts as a surfactant modifying the Ni growth. Scanning Tunneling Microscopy (STM), as well as Reflectance Difference Spectroscopy (RDS) are used to characterise the sample properties. The sensitivity of the RDS to the polar Magneto-Optic Kerr Effect has been exploited (RD-MOKE). Contrary to growth on pristine Cu(110), thin Ni films on oxygen covered Cu(110)- (2x1)O show a spin reorientation transition from in-plane to out-of-plane magnetisation at 9 ML Ni coverage. For Ni films evaporated on the Cu-CuO stripe phase, which consists of a periodic array of (2x1) reconstructed CuO stripes separated by bare Cu, the magnetic easy axis lies completely in-plane up to a coverage of 22.5 ML. Exceeding this coverage, a small remanent magnetisation component pointing out-of-plane evolves. Upon postgrowth oxygen exposure the Ni film becomes completely out-of-plane magnetised and the out-of-plane remanence and coercive field strongly increase during exposure. STM images show a fully (2x1)O reconstructed surface after the oxygen exposure, but no morphological changes of the Ni film. We thus conclude that the oxygen strongly modifies the surface magnetic anisotropy. (author)