Optical anisotropy and magneto-optical properties of Ni on preoxidized Cu(110)

We investigate the growth mode and the magnetism of Ni on Cu(110) substrates using oxygen as a surfactant. Layer by layer growth on oxidized Cu(110) is obtained, in contrast to the island growth found on clean Cu(110) substrates. The main emphasis of our work addresses the potential of optical spectroscopy for analyzing structure and magnetism. For that purpose we use a spectrometer which allows us to record reflectance anisotropy (RAS) and magneto-optic Kerr (MOKE) spectra simultaneously and in situ during film growth, in the spectral range from 0.72 to 6.5 eV. We show that RAS is very useful for monitoring the growth of Ni on Cu(110), since it reveals information on the atomic surface structure and on the strain evolution during the growth process. MOKE, on the other hand, is sensitive to the magnetic properties of the epitaxial Ni film. Combining RAS and MOKE thus allows us to directly relate growth mode and magnetic properties and to identify correlations in between. As such, an out-of-plane magnetization for Ni films between 7.5 and 35 ML thickness is observed, correlated with a flat layer morphology, i.e., two-dimensional growth mode of the Ni film. Above 35 ML roughening sets in and the magnetization direction rotates towards in-plane orientation again. Well below 35 ML, between 14 ML and 18 ML of Ni, the strain due to pseudomorphic growth is relaxed, correlated with a strong increase in coercivity due to dislocation formation. Mandatory for a meaningful analysis of the Voigt parameter of Ni is the sophisticated optical modeling of the layer system. Doing so, we prove that a modification of electronic properties (d-band narrowing) of the Ni film in the pseudomorphic growth regime does not occur, in contrast to expectations.