Tunneling giant magnetoresistance in heterogeneousFe−SiO2granular films

Abstract

Magnetic and transport properties are examined for heterogeneous ${\mathrm{F}\mathrm{e}-\mathrm{S}\mathrm{i}\mathrm{O}}_2$ granular films prepared on glass substrates by rf sputtering. The superparamagnetic nature and the tunneling giant magnetoresistance are observed in the films having Fe volume fractions smaller than 45%. The magnetization and magnetoresistance (MR) curves are systematically analyzed by the summation of two Langevin functions. The dependence of the MR ratio on the Fe volume fraction is explained phenomenologically by the distance between the nearest-neighbor grain surfaces. The temperature dependence of the MR ratio is also discussed.