Gilbert Damping in Ni/Co Multilayer Films Exhibiting Large Perpendicular Anisotropy

Gilbert damping is reported in perpendicularly magnetized Ni/Co multilayer films with Pt buffer and capping layers, and investigated through the time-resolved magneto-optical Kerr effect under various applied magnetic field strengths and directions. Both damping constant alpha and perpendicular magnetic anisotropy energy K(u) depend strongly on layer thickness and bilayer periodicity, and rise to approximately 0.08 and 8 Merg/cm(3), respectively. The Gilbert damping rate depends linearly on inverse multilayer thickness, indicating that large damping in the Ni/Co multilayers stems from its interfaces in contact with the Pt layers. (C) 2011 The Japan Society of Applied Physics