Giant magnetoresistance in granular Fe-SiO2 films

We studied resistivity, magnetoresistivity and magnetization in granular Fe-SiO2 films. In the hopping region, magnetoresistance was found to be as large as - 5%, and is isotropic for different measurement geometry, which is the signature of giant magnetoresistance due to a spin-dependent conduction process. Temperature dependence of magnetoresistance could be described qualitatively but not quantitatively by two specific spin-dependent tunnelling models. We found that resistivity rho changes five orders of magnitude by altering measurement temperature, annealing temperature or metal volume fraction, and that magnetoresistivity -Delta rho increases with rho monotonously.