Effect of alloy composition on the thermodynamic and kinetic parameters of the A1 to L1 transformation in FePt, FeNiPt, and FeCuPt films

Abstract

Differential scanning calorimetry is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 39.3−55.3 at. % Pt and ternary FePt-based films with additions of Cu up to 20 at. % and Ni up to 25 at. % for a range of Fe/Pt ratios. For FePt and FeCuPt, these are extensions of previously studied ranges [K. Barmak, J. Kim, D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005)]. Parameters including the A1 and L10 phase Curie temperatures, the kinetic ordering temperature, the activation energy, and the transformation enthalpy are reported. For FePt, the L10 Curie temperature reaches a maximum of 457 °C near 45 at. % Pt. In contrast, the A1 Curie temperature has an essentially constant value of 300 °C across the full composition. Both the kinetic ordering temperature and activation energy show a minimum near 46 at. % Pt, while the magnitude of the transformation enthalpy has its maximum near 50 at. % Pt. Ni additions to FePt in general lower the L10 Curie temperature, but they increase the A1 Curie temperature. The kinetic ordering temperature and the activation energy increase for all Ni additions, whereas the transformation enthalpy decreases measurably only for Ni additions over ∼10 at. %. Cu additions to FePt act as magnetic diluents regarding both the A1 and L10 phase Curie temperatures, with increased Cu content resulting in decreased Curie temperature. Conversely, Cu additions have no significant effect on the kinetic ordering temperature, activation energy, or transformation enthalpy when compared to equivalent binary alloys. The relevance of our findings to alloy development for ultrahigh density magnetic recording media is discussed, with specific focus on the potential for heat-assisted magnetic recording.