Dynamic stress-induced low-temperature ordering of FePt

Abstract

The ordering temperature of FePt was significantly reduced to 275°C by introducing a Cu underlayer on the HF-cleaned Si(001) substrate. A coercivity Hc as high as 6200Oe can be achieved after postannealing at 275°C, and Hc can be further increased to 7000Oe after 300°C postannealing. During the formation of copper silicide Cu3Si, the expanded volume induces a dynamic in-plane tensile stress on FePt films, which accelerates the formation of the ordered FePt phase at low temperature. Different from the static stress induced by the lattice mismatch between films and underlayers, the dynamic stress is relaxed after the formation of Cu3Si is completed; therefore, the low-temperature ordering of FePt mainly takes place simultaneously with the evolution of dynamic stress during the formation of Cu3Si. The coercivity of FePt depends on the amount of Cu3Si and on the stress developed by Cu3Si.