Magnetic properties and inhomogeneous phase transition in (Fe _xCo _0.5-x)Pt _0.5 films

(Fe _xCo _0.5-x)Pt _0.5 ternary thin films were deposited on glass substrates by using a dc sputtering method at room temperature and were subsequently annealed at 700 °C in a high vacuum. A high degree of the (111) preferred orientation could be obtained in all the as-deposited films and was not destroyed, even though post annealing. The CoPt and the FePt binary alloys were completely mixed and had a L1 _o-type ordered structure, as confirmed by single (222) peaks and by the linear variation of the lattice constant a _o. The ordered structure of the FePt alloy was thought to have formed from the disordered structure by an inhomogeneous process, which was confirmed by the asymmetric peak shapes. The lattice parameter a _o varied linearly with the Fe content while the coercivity showed a minimum value at the equiatomic composition of the Fe and the Co atoms.