Calorimetric studies of the A1 to L1 transformation in FePt and related ternary alloy thin films

Abstract

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 47.5 to 55 at. % Fe, and in ternary alloys of FePt with Cu, Co, Ag, and Au. The lowest kinetic ordering temperatures, in the range of 355–375 °C, are found for Fe-rich binary FePt alloys, namely, Fe53Pt47 and Fe55Pt45, and for ternary FePt-Cu alloys that have the same amount of Pt as these binary alloys, namely, Fe50Cu3Pt47 and Fe50Cu5Pt45. Ternary additions of Co (28 at. %), Ag (11 at. %), and Au (7 and 12 at. %) increase the kinetic ordering temperature when compared to the equiatomic, binary FePt alloy. The activation energies of ordering lie between 1.6 and 1.9 eV, except for the Fe47Pt46Au7 alloy, for which the activation energy is 2.2 eV. The transformation enthalpies are in the range of −6.3 to −13.2 kJ/g atom. The Curie temperatures for the binary FePt alloys increase from 379 to 456 °C in the composition range 47.5 to 55 at. %. Ternary additions have a complex effect on the Curie temperature. However, the Curie temperatures of the ternary Fe-Pt-Cu alloys, with Cu additions of 1–5 at. %, were lower (370–407 °C) than the binary FePt alloys of equal Pt content. Au is seen to phase separate from FePt.