The progressive evolution from giant magnetoresistance to anisotropic magnetoresistance in CoNi-Al2O3 granular films

A series of CoNi-Al2O3 granular films were prepared with a magnetron controlled sputtering system. The magnetic-transport properties were measured by conventional four probes method. The results indicate that longitudinal GMR effect reaches a maximum of -2.1% at about 35 vol.% CoNi. Meanwhile, GMR effect is dominant when the volume fraction is less than about 50 vol.%, whereas AMR predominate in films when the volume fraction is larger than about 50 vol.%. It suggests that there exists a progressive evolution from GMR to AMR through percolation region in CoNi-Al2O3 granular films.