Effects of Pt addition on the magnetic and microstructural properties of CoC granular films

The magnetic properties and microstructures of granular Co_60-XPt_XC₄₀ (0⩽x⩽23) thin films, fabricated by ion-beam sputtering and subsequent annealing, were investigated. High coercivity was obtained in samples with Pt concentrations ranging from 12 to 16 atomic percent, with a maximum coercivity of 1800 oersteds. These films consisted of CoPt grains having a CoPt disordered alloy phase, which were separated by a C phase. The magnetic grains had an average size of 10 nm and a faulted hexagonal close-packed structure. Below 16 at.% Pt content, the improvement in coercivity with Pt was most likely related to an increase in the magnetocrystalline anisotropy of the CoPt alloy compared to that of the Co. Above 16 at.% Pt content, a drastic decrease in coercivity was observed. It is found that for these large Pt concentrations a higher annealing temperature is required to improve the coercivity with Pt addition