Evolution of structural and magnetic properties of FePtCu alloy films on annealing of FePt/Cu multilayers

Thin films of ternary (FePt)(100-x)Cu(x)alloys were obtained by annealing of FePt (100 angstrom)/Cu (d angstrom) multilayers withd= 50 and 100 angstrom deposited by sputtering at room temperature on Si substrates. The evolution of structural 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 h at different temperatures (300 to 600 degrees C) showed very low interdiffusion at the interfaces with no signature of alloy phase formation. However, isothermal annealing of multilayers at 600 degrees C for longer times (1.5-6.5 h) showed significantly large interdiffusion accompanied by the formation of polycrystalline ternary alloy and iron silicide phases. The iron silicide formed at the substrate-film interface assists the growth of theL1(0)ordered ternary alloy phase, which showed different stoichiometry for different multilayers. TheL1(0)phase formed with higher Cu content showed drastically different magnetic properties with a reduction in saturation magnetization and an increase in coercivity (similar to 6 kOe) at room temperature. The iron silicide formed on high temperature annealing showed ferromagnetic nature with a magnetization of similar to 140 emu cm(-3)at room temperature.