Magnetic anisotropy of the ultrathin Fe layers in Fe/NiFe/Fe/Cu multilayers and their effect to the magnetoresistance

The effects of the deposition of ultrathin 57Fe layers on both sides of the NiFe layers in NiFe/Cu multilayers were investigated by focusing on their structural, magnetic and magnetoresistance properties. Conversion electron Mössbauer spectroscopy measurements showed an out-of-plane magnetic anisotropy of the Fe layers. The magnetoresistance curves showed an unusual shape, where up to three peaks were observed. Eight variables computer simulations, based on a phenomenological model that considers bilinear and biquadratic couplings between layers with cubic and in-plane uniaxial anisotropies, were used in order to calculate the best-fitting magnetization curves for the NiFe/Cu and Fe/NiFe/Fe/Cu multilayers. Both model and Mössbauer spectroscopy results showed that it is the rotation of the Fe magnetic moment from out-of-plane to in-plane orientation that provokes the unusual magnetoresistance curve shape. The observed reduction of the magnetoresistance amplitude with the addition of one monolayer of Fe in the NiFe/Cu multilayer was attributed to a less-effective spin-dependent scattering that occurs at Fe/Cu and Fe/NiFe interfaces than at the NiFe/Cu interfaces.