Magnetic properties of ultrathin epitaxial Co films on a Pd (111) single crystal

Detailed magnetic studies were made of ultrathin epitaxial Pd/Co bilayers grown by evaporation in UHV on a Pd(111) single crystal. The magnetic properties were studied by polar Kerr hysteresis loops, vibrating sample magnetometry, and ferromagnetic resonance (FMR) at 10 and 34 GHz. The 10-GHz measurements were carried out from room temperature to 1.6 K. The effective anisotropy fields were determined from the FMR. All the magnetic measurements showed that Co films thinner than ∼9 monolayers had an easy magnetization axis perpendicular to the film plane. It was deduced that the first-order uniaxial interface and volume anisotropy constants were, respectively, 0.8±0.05 mJ/m2 and (4 ± 1) × 105 J/m3 at room temperature. The dependence of the FMR lineshape on the angles of the applied fields was analyzed by calculating the FMR response. The observed effects could be explained by allowing for a spread in the magnetic anisotropy throughout the sample.