Ta Doping Effect in Co60C40 Thin Films

Abstract

(Co60C40)1-x Tax films (0% ≤ x ≤ -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 ° for 30 min) become magnetically hard with Hc ranging from 480 to 780 Oe and Ms changing from 480 to 600 emu/cm3. Both Hc and Ms 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 Hc and Ms. After annealing at 300 °, Hc of (Co60C 40)97Ta3 films increases from 0 to about 380 Oe, while almost no changes are observed for Co60 C40 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.