CoNbFe soft magnetic thin-film backlayers for glass computer disks

Co84Nb12Fe4 films with very low coercivity down to 1 A/m, anisotropy field 1100 A/m, and saturation magnetic induction 1.1 T have been deposited by rf sputtering onto chemically strengthened glass disk substrates as a backlayer for perpendicular recording Winchester disks. Values of coercivity and anisotropy field were studied over a thickness range from 30 to 15 000 Å and found to be a strong function of film thickness. Comparisons between Néel’s prediction for wall motion coercivity mechanism and the experimental data were made. The experimental coercivity fits the Néel formula when films are thicker than 400 Å. The dependence of coercivity and anisotropy field on deposition conditions was also characterized. The thermal stability of the films was studied by differential scanning calorimetry (DSC) and by thermal annealing up to 500 °C. The crystallization temperature of the CoNbFe films is about 450 °C determined from DSC analysis. Thermal annealing revealed that the magnetic properties were very stable when the annealing temperature was below 400 °C.