Evolution of structure and magnetic properties of FePtCu alloy films on annealing of FePt/Cu multilayers
Thin films of ternary (FePt)100-xCux alloys were obtained by annealing of FePt (100 Å)/Cu (d Å) multilayers with d = 50 and 100 Å deposited by sputtering at room temperature on Si substrates. The evolution of structure and magnetic properties of these multilayers induced by isochronal and isothermal annealing in a vacuum has been studied using depth dependent characterization techniques. Isochronal annealing for 0.5 hr at different temperatures (300 to 600 oC) showed very low interdiffusion at interfaces with no signature of alloy phase formation. However, isothermal annealing of multilayers at 600 oC for longer times (1.5 – 6.5 hr) has shown significantly large interdiffusion accompanied by the formation of polycrystalline ternary alloy and iron silicide phases. The iron silicide formed at the substrate-film interface assist the growth of L10 ordered ternary alloy phase, which showed different stoichiometry for different multilayers. The L10 phase formed with higher Cu content showed drastically different magnetic properties with a reduction in saturation magnetization and an increase in coercivity (~ 6 kOe) at room temperature. The iron silicide formed at high temperature annealing showed ferromagnetic nature with a magnetization of ~140 emu/cc at room temperature.