We report a comparative study of the magnetic and magnetoresistance phenomena in two types of granular ferromagnets: ferromagnet-normal-metal mixtures Ni-Ag, Co-Ag, and ferromagnet-insulator mixtures Ni-${\mathrm{SiO}}_2$ , Co-${\mathrm{SiO}}_2$ . Anisotropic magnetoresistance and giant magnetoresistance (GMR) are identified in both types of systems above and below the magnetic component percolation threshold respectively. The GMR effect in granular ferromagnets is shown to be essentially independent of the nature and resistance of the nonmagnetic intergranular matrix.

DOI:https://doi.org/10.1103/PhysRevB.55.6446