Lattice dynamics and migration enthalpies in CoPt3 and FePd

概要

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The frequencies of the normal modes of vibration of CoPt3 and FePd single crystals have been measured using inelastic neutron scattering. The measurements were performed in the L12 ordered phase (at 300 and 930 K) for CoPt3 and in the L10 ordered phase (at 300 and 860 K) for FePd. Dispersion curves were also measured in the fcc disordered states, at 1060 and 1020 K for CoPt3 and FePd, respectively. The activation enthalpy of atomic migration has been evaluated from the phonon density of states by applying Schober's model [H. R. Schober et al., J. Phys.: Condens. Matter 4, 9321 (1992)] and its extension to the L12 ordered structure. The phonon properties of FePd3 reported in the literature have been analyzed similarly and are compared with the results for CoPt3 and FePd. The contribution of the long-range order to the migration enthalpy estimated in the present analyses agrees well in magnitude with the previous evaluation by Monte Carlo simulation for alloys of the fcc, L12, and L10 structures.