Polar Kerr-effect observation of perpendicular surface anisotropy for ultrathin ferromagnetic films: fcc Fe/Cu(100)

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Abstract
The theoretically predicted prependicular surface anisotropy of ultrathin ferromagnetic Fe films has been confirmed using the magneto-optical Kerr effect. Polar and longitudinal Kerr-effect measurements have been performed in situ on the same fcc Fe/Cu(100) films to study the dependence of the magnetic properties on film thickness and growth temperature conditions. Auxiliary LEED and Auger studies are used to characterize the structure and growth of the films. For films 1.2–5.9 monolayers (ML) thick grown at ∼100 K, for instance, square hysteresis-loop behavior in the polar Kerr effect confirmed the dominance of the perpendicular surface anisotropy. Examples are presented to document how the polar and longitudinal Kerr-effect signals evolve for films thicker than 6 ML due to the easy axis reorienting into the film plane. To differentiate between intrinsic temperature effects and those associated with interfacial compositional changes, the films were thermally cycled and their Kerr signals monitored. Films of thickness around 4 ML retained their characteristic polar Kerr-effect square loops despite thermal cycling between ∼100 and ∼400 K, while those <2 ML thick changed irreversibly. These studies confirm that intermixing can be limited to the monolayer range by low-temperature growth conditions, but the LEED results show that the degree of structural ordering of the films is reduced, as expected.