The frequencies of the normal modes of vibration of CoPt 3 and FePd single crystals have been measured using inelastic neutron scattering. The measurements were performed in the L1 2 ordered phase ͑at 300 and 930 K͒ for CoPt 3 and in the L1 0 ordered phase ͑at 300 and 860 K͒ for FePd. Dispersion curves were also measured in the fcc disordered states, at 1060 and 1020 K for CoPt 3 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 ͑1992͔͒ and its extension to the L1 2 ordered structure. The phonon properties of FePd 3 reported in the literature have been analyzed similarly and are compared with the results for CoPt 3 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, L1 2 , and L1 0 structures.

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