EXCHANGE-COUPLED MBE-GROWN CO CU/CO(111) TRILAYERS/

It is shown that the high-field curvature in the in-plane and polar ma gnetization curves of exchange-coupled MBE-grown Co/Cu/Co(111) structu res can be accurately fitted by assuming a sizeable biquadratic coupli ng in addition to the bilinear coupling, and the existence of a large areal fraction of ferromagnetic inclusions. Measurements on a sample w ith a single Co layer confirm that the curvature does not originate fr om the individual Co layers. Analysis of two Co/Cu/Co(111) trilayers w ith different Co-Cu interface qualities, as measured by NMR, shows sig nificantly higher bilinear and biquadratic coupling strengths for the trilayer with the better defined Co-Cu interfaces. While NMR indicates reasonably good structural quality on a short lateral length scale, p olar Kerr measurements as a function of interlayer thickness, and pola rized neutron reflection measurements, indicate the existence of struc tural imperfections on a long lateral length scale.