The frequencies of the normal modes of vibration of ${\mathrm{CoPt}}_3$ and FePd single crystals have been measured using inelastic neutron scattering. The measurements were performed in the $\mathrm{L}{1}_2$ ordered phase (at 300 and 930 K) for ${\mathrm{CoPt}}_3$ and in the $\mathrm{L}{1}_0$ 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 ${\mathrm{CoPt}}_3$ 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 (1992)] and its extension to the $\mathrm{L}{1}_2$ ordered structure. The phonon properties of ${\mathrm{FePd}}_3$ reported in the literature have been analyzed similarly and are compared with the results for ${\mathrm{CoPt}}_3$ 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, $\mathrm{L}{1}_2,$ and $\mathrm{L}{1}_0$ structures.

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