CoPt films grown on MgO(001) substrates by molecular-beam epitaxy are expected to develop a very large uniaxial magnetocrystalline anisotropy and a high coercivity when the [001] single variant L10 structure develops along the growth direction. The present study investigates the growth conditions that provide the best structural quality of the films and their related magnetic properties. The quality of the substrate surface, the thickness, and the texture of the Pt buffer layer, the presence or absence of a Cr seed layer, are found to be determinants for the fraction of well-oriented grains in the films, whereas the growth temperature mainly pilots the degree of L10 order η. The uniaxial magnetocrystalline anisotropy energy of the [001] grains (Ku001) is maximum at the stoichiometric composition and shows a linear increase with η. The coercive fields and the magnetic domain size are discussed in relation to the microstructure, the degree of L10 order and the magnetic microscopic constants of the films.

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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