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 A1 to L10 transformation in FePt and CoPt thin films have been measured as −10.2±2.1 kJ/g -atom (1.7±0.1 eV) and −3.1±0.2 kJ/g-atom (2.8±0.2 eV), 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.

Phase transformations and thermodynamic properties of nanocrystalline FePt powders

“…Therefore, one could expect that in the studied FePt powders diffusion over the grain boundaries is a determining factor for the phase transformations, ordering and grain growth. The obtained activation energies are comparable to those found for the A1 → L1 0 transformation in sputter deposited FePt fi lms [10] and [11].…”

“…The mechanisms of phase formation and ordering (i.e. continues or discontinues) differ depending on the approach used to obtain the L1 0 phase [5], [6], [9], [10] and [11]. In the present work, we investigate structural transformations occurring upon milling and subsequent annealing of the FePt powders.…”

Phase Transformation and Magnetic Hardening in Isolated FePt Nanoparticles

“…7(b). The obtained activation energy of the particles without surfactant addition is 2.07 ± 0.09 eV, which is quite similar to that of the FePt thin films [24], [25]. However, the activation energy of the particles with surfactant additions significantly increased to 2.87 ± 0.15 eV, which is of about 38% enhancement.…”

Curie temperatures of annealed FePt nanoparticle systems

“…% Fe. [11][12][13] More interestingly, reduction of T C with decreasing dimension of the materials has also been observed in L1 0 FePt nanoparticles 14 and other ferromagnets. 15,16 In order to understand magnetic ordering of the nanostructured ferromagnetic phases in a wide compositional range, the annealed FePt nanocrystalline films deposited by nanoparticles have been studied with a composition range of 15-90 at.…”