Experimental measurements of the heats of formation of Fe3Pt, FePt, and FePt3 using differential scanning calorimetry

Abstract

Using differential scanning calorimetry (DSC), the heats of formation of Fe3Pt, FePt, and FePt3 were determined from the reaction of sputter deposited Fe/Pt 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, Fe3Pt, 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 FePt3, 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.