Experimental measurements of the heats of formation of Fe_3Pt, FePt, and FePt_3 using differential scanning calorimetry

摘要

Using differential scanning calorimetry (DSC), the heats of formation of Fe_3Pt, FePt, and FePt_3 were determined from the reaction of sputter deposited Fe_3Pt multilayer thin-films with a periodicity of 200 nm but different overall compositions. Film compositions were measured by energy dispersive x-ray spectrometry. The phases present along the reaction path were identified by x-ray diffraction. For the most Fe-rich phase, namely, Fe_3Pt, the measured enthalpy of formation was -9.3 ± 1.3 kJ/mol in a film with a composition of 70.4:29.6 (±0.2 at. %) Fe:Pt. For FePt, the measured enthalpy of formation was -27.2 ± 2.2 kJ/g-atom in a 49.0:51.0 (±0.5 at. %) Fe:Pt film. For FePt_3, which is the most Pt rich intermetallic phase, the measured enthalpy of formation was -23.7 ± 2.2 in a film with a composition of 22.2:77.8 (±0.6 at. %) Fe:Pt. The reaction enthalpies for films with Fe:Pt compositions of 44.5:55.5 (±0.3 at. %) and 38.5:61.5 (±0.4 at. %) were -26.9 ±1.0 and -26.6 ± 0.6 kJ/g-atom, respectively, which taken together with the value for the 49.0:51.0 film demonstrate the relative insensitivity of the reaction enthalpy to film composition over a broad composition range in the vicinity of the equiatomic composition. The experimental heats of formation are compared with two sets of reported first-principles calculated values for each of the three phases at exact stoichiometry.