Calorimetric studies of the A1 to L1 transformation in FePt and CoPt thin films

Abstract

Using differential scanning calorimetry, the enthalpy (activation energy) for the $\text{A1}$ to ${\text{L1}}_0$ transformation in FePt and CoPt thin films have been measured as $\text{−10.2±2.1\hspace{0.17em}}\mathrm{kJ/g -atom}$ $\text{(1.7±0.1\hspace{0.17em}}\mathrm{eV})$ and $\text{−3.1±0.2\hspace{0.17em}}\mathrm{kJ/g-atom}$ $\text{(2.8±0.2\hspace{0.17em}}\mathrm{eV}\mathrm{),}$ respectively. FePt is further seen to transform at temperatures that are approximately 120 °C lower than those for CoPt. The enthalpy of grain growth that accompanies the transformation is shown to be negligibly small by comparison to the transformation enthalpy in both films. The impact of our findings on alloy development for ultrahigh density magnetic storage media is discussed.