Effect of random anisotropy on magnetization reversal in dipolarly coupled layered thin films

•Presence of random anisotropy in addition to uniaxial anisotropy has been observed.•Layer-by-layer magnetization reversal has been experimentally observed.•The experimental results have been reproduced by OOMMF micromagnetic simulations.•Our work may have significant effect in magnetic thin films and multilayers. Magnetic thin films and multilayers offer many novel physical phenomena with tremendous potential for applications. Various growth processes and methods are in place to make homogeneous films. However, dispersion in local easy axes is an inherent issue which may give rise to an effective random anisotropy in thin film. It is important to investigate the effect of random anisotropy on the magnetic properties of the thin films. In this report we address the aspect of local dispersion induced random anisotropy on magnetization reversal in ferromagnetic (FM)/non-magnetic(NM)/ferromagnetic(FM) stacks. We show that the magnetization reversal is not only governed by the inter-layer interaction but the intrinsic anisotropies also play a crucial role. In this context we have studied the magnetization reversal of Co/AlOX/Co trilayers with various thicknesses of AlOX which acts as a spacer between the two Co layers. Presence of random anisotropy in addition to growth induced uniaxial anisotropy was observed in all the samples. Magneto-optic Kerr effect (MOKE) based microscopy revealed dipolar-coupled layer-by-layer magnetization reversal of the Co layers which was corroborated by polarized neutron reflectometry (PNR) experiments. Micromagnetic simulations confirmed that the presence of random anisotropy in addition to uniaxial anisotropy leads to layer-by-layer magnetization reversal.