Ta doping effect in Co/sub 60/C/sub 40/ thin films

(Co/sub 60/C/sub 40/)/sub 1-x/Ta/sub x/ films (0/spl les/x/spl les/-10%) with thickness of 30 nm were cosputtered onto C-buffered glass substrates at room temperature. The as-deposited films are structurally amorphous and nonferromagnetic. The annealed films (400/spl deg/C for 30 min) become magnetically hard with H/sub c/ ranging from 480 to 780 Oe and M/sub s/ changing from 480 to 600 emu/cm/sup 3/. Both H/sub c/ and M/sub s/ increase with Ta concentration as x<3%, show peaks at x=3%, and then decrease with Ta concentration. This is because a small amount of Ta doping might enhance the diffusion of carbon in the films and thus form more cobalt grains upon annealing. However, doping more Ta (x>3%) destroys the Co structure and this causes the drop in both H/sub c/ and M/sub s/. After annealing at 300/spl deg/C, H/sub c/ of (Co/sub 60/C/sub 40/)/sub 97/Ta/sub 3/ films increases from 0 to about 380 Oe, while almost no changes are observed for Co/sub 60/C/sub 40/ films. Doping in a Co-C system with a larger atom such as Ta may be a way to enhance the segregation of Co and C and, therefore, reduce phase segregation temperature.