Calorimetric studies of the A1 to L1_0 transformation in binary FePt thin films with compositions in the range of 47.5-54.4 at. % Fe

摘要

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L1_0 ordering transformation in binary FePt films with compositions in the range of 47.5-54.4 at. % Fe. The kinetic ordering temperature, taken as the calorimetric peak temperature at a heating rate of 40℃/min, decreases from 447 to 357℃ in this composition range. In contrast with the kinetic ordering temperature, the Curie temperature of the L1_0 ordered phase increases from 384 to 455℃ as the Fe content is increased. The activation energies of ordering lie between 1.4 and 2.0 eV, and the transformation enthalpies are in the range of -8.2 to -13.6 kJ/g-at. The Avrami exponent for the transformation is lower than expected and lies in the range of 1.1-1.8. The lattice parameter of the Al phase and the c/a ratio of the L1_0 phase decrease with increasing Fe content.