Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity

We report a study of the structural and magnetic behavior of the topmost magnetic layer in a ferromagnet-nonmagnet (Co-Au) multilayer system. Glancing angle X-ray diffraction measurements performed on a series of multilayers showed a gradually increasing degree of amorphization of the topmost magnetic layer with increasing number of bilayers. Concurrently, the magnetic hardness and magneto-crystalline anisotropy of the top Co layer were found to decrease, as observed by magneto-optical Kerr effect measurements. This magnetic softening has been discussed in the light of Herzer's random anisotropy model. Micromagnetic simulations of the multilayer system also corroborated these observations.