Magnetic Properties of Sputtered Co-Pt Alloy Films

The structure and magnetic properties of Co-Pt alloy thin films were investigated under various sputtering conditions. Co-Pt films with less than 15 at% Pt' had an hep structure, and above 30 at% Pt had an fcc structure. Both hep and fcc phases were identified in films with between 15 and 30 at% Pt. A perpendicular magnetization was observed at compositions between 20 and 40 at% Pt. A substrate bias voltage of -50 V improved the orientation of the fcc [111] axis normal to the film plane and increased the perpendicular anisotropy energy K
_u
. There was also a correlation between the orientation of crystallites and K
_u
when the Ar gas pressure P
_Ar
was varied. This suggested that the perpendicular anisotropy of Co-Pt films arises from the magnetocrystalline anisotropy. Although the perpendicular coercivity was small in these films, it increased by a factor of two with the addition of 10 at% Cr.