Enhancement of L10 transformation in Fe/Pt multilayer by Cu addition

Abstract

Enhancement in L10 transformation kinetics in FePt is achieved by incorporating an optimum concentration of ternary element Cu, which has limited solubility in the fcc FePt phase, into the FePt multilayer stack. Two different multilayer structures were deposited. In first multilayer Cu is deposited at one interface of Fe/Pt and in other Cu is alloyed with Fe and Pt layers by co-sputtering. One Fe42.5Pt42.5Cu15 alloy film is also prepared and detailed study of evolution of structural and magnetic properties as a function of isochronal annealing is done using XRD and Magneto Optic Kerr Effect (MOKE) measurements respectively. Annealing up to 200oC results only in intermixing in the multilayer structure, with no sign of L10 transformation. Annealing at 300oC for 1h results in partial transformation to L10 phase as evidenced by appearance of (001) superlattice peak as well as large increase in the coercivity. It is found that in the Fe(Cu)/Pt(Cu) multilayer exhibits significantly faster L10 transformation as compared to Fe/Pt/Cu multilayer or FePtCu alloy film. Inter-diffusion study using x-ray reflectivity measurements reveals that constant for interdiffusion in Fe(Cu)/Pt(Cu) is only marginally higher than that in Fe/Pt/Cu multilayer. The observed enhancement in L10 transformation rate in Fe(Cu)/Pt(Cu) multilayer is discussed in terms of possible enhancement of diffusivities of constituent species in fcc FePt phase.