EFFECT OF Au UNDERLAYER ON STRUCTURAL AND MAGNETIC PROPERTIES OF CoPt THIN FILMS

CoPt and CoPt/Au films prepared by magnetron sputtering were studied in this paper. The films were deposited at room temperature and then a post annealing was applied at temperatures (T(a)) from 400 degrees C to 800 degrees C. The structure results showed that the ordering transformation occurred at T(a) = 500 degrees C in the Au-underlayered films, which is 100 degrees C lower than that in the single layer CoPt samples. The scanning electron microscopy (SEM) study indicates an Au:CoPt composite structure with increased grain size was formed in Au/CoPt films when T(a) exceeded 500 degrees C where the ordering begins together with the magnetic hardening, which suggests that the gold layer may improve the ordering by enhancing the diffusion of CoPt. The best ordering was obtained at T(a) = 700 degrees C, the order parameters were 0.56 and 0.88 for CoPt and CoPt/Au, respectively. As T(a) was increased to 800 degrees C, a drastic lattice distortion was observed. The tetragonal lattice of the Ll(0) phase was found to transform into a cubic structure, resulting in a magnetic softening. The mechanism of this distortion is unclear and the atomic ordering of this cubic phase needs further investigation.