Dependence of grain sizes and microstrains on annealing temperature in Fe/Pt multilayers and L10 FePt thin films

Fe/Pt multilayers (MLs) with an overall composition Fe52Pt48, deposited by magnetron sputtering on thermally oxidized Si wafer substrates, were post annealed in vacuum at various temperatures (TA) in the range 573–973 K. The MLs transform directly and completely into polycrystalline hard-magnetic FePt thin films with ordered L10 structure above TA = 573 K. The evolution of the microstructure, the order parameter and the stacking fault density with annealing temperature was investigated by ex-situ X-ray diffraction and line-broadening analysis. The average microstrains of the thin films are relatively small ( ~ 0.2%) and remain practically constant as a function of TA. The thin films show anisotropic size-broadening and grain growth: fast growth rate along the [221] direction and a slow growth rate along the [001] direction. The annealing temperature dependence of the average grain size could be described by a grain growth model with grain growth exponent n = 3 ± 0.5 and activation energy 0.51 ± 0.07 eV.