Effects of interfacial Ru, Pd, Ag, and Au insertion layers on the anisotropic magnetoresistance in Ta/NiFe/Ta trilayers

Abstract

Ta/NiFe/Ta trilayers are commonly used in various commercial sensors based on anisotropic magnetoresistive(AMR) effect. Technologically it is desirable to reduce NiFe film thickness to diminish the demagnetization effect for the smaller and smaller devices. However, the AMR ratio of thin NiFe film decreases rapidly with film thickness decreasing when the NiFe film is thinner than 20 nm. Our previous work revealed that the AMR ratio and the thermal stability of Ta/NiFe/Ta trilayers can be significantly improved through interfacial Pt addition due to the enhanced interfacial spin-orbit scattering and the suppressed magnetic dead layers. In this paper, 4d and 5d elements including Ru, Pd, Ag and Au, are also introduced at the interfaces of Ta/NiFe/Ta films fabricated by DC magnetron sputtering. It is found that the insertion of interfacial Pd layers leads to an appreciable AMR enhancement in the as-sputtered state and after annealing. Insertion layers of Ag and Au with small surface energy and relatively low melting point suffer from thermal interdiffusion and seriously deteriorate the AMR of the annealed films, whereas Ru insertion layers exhibit improved thermal stability. The present results indicate that the AMR of Ta/NiFe/Ta films can be notably affected by the extremely thin interfacial insertion layers due to the changed interfacial spin-orbit scattering, magnetic dead layer and atomic interdiffusion.