Magnetic properties and phase stability in Co-Ni base alloy thin films

Co-Ni base thin films were deposited by reactive radio frequency magnetron sputtering in N-2 + Ar atmosphere at different P-N2/P-Ar partial pressure ratios. Only the nitrogen content in the films changes when changing P-N2/PAr. Amorphous magnetic films can be obtained for compositions around N/Co = 1-1.5, whereas higher N2 contents lead to nonmagnetic nitride phases. Significant changes in structural and magnetic properties are observed upon heating thin films in a TG(M) apparatus. Only the sample having a N/Co=1.5, when heat treated, appears to be made of a stable ferromagnetic phase. The N content is appropriate to keep Cr, Al and N, which exert an adverse effect on the magnetization of Co-Ni base alloys, out of the ferromagnetic phase in the form of separated nitride phases.