EFFECT OF AN AU UNDERLAYER ON PERPENDICULAR MAGNETIC-ANISOTROPY IN AUCO/AU(111) SANDWICH FILMS/

We have used spin-wave Brillouin scattering to study perpendicular mag netic anisotropy in Au/Co/Au(111) sandwiched films with varying thickn esses of Au-underlayers. By using 5-monolayer (ML) -thick Co films, th e transition of spin-wave frequency between out-of-plane and in-plane magnetizations can be observed by varying the in-plane field. We find that the field-dependence of the spin-wave energy is explained by a ca lculation including both the first-order (second power) and the second -order uniaxial perpendicular anisotropies depending on the Au-underla yer. We observe saturation of the anisotropy at 5 ML of Au-underlayer thickness, which corresponds to the saturation of in-plane lattice exp ansion of Co on that Au-underlayer. The contribution of interface anis otropy is evaluated from the Co-thickness dependence of the anisotropy observed. We also have observed a field-dependent broadening of the s pin-wave Brillouin spectra at a critical field between out-of-plane an d inplane magnetizations, which we attribute to a distribution of the first-order anisotropy.