Magnetic and transport properties of granular Fe-MgF2 films

Magnetic properties and magneto resistance (MR) have been investigated in granular Fe-MgF2 films, which consist of metallic particles embedded in an insulating medium. Magnetization curves in the superparamagnetic state are reproduced by considering magnetic dipole interactions between particles. A large negative MR of about 7% at 78 K is observed in semiconducting films with the Fe composition below the percolation threshold. The field dependence of the MR is well described by the square of the magnetization. The MR effect in this system is ascribed to the tunneling conductance between the Fe particles depending on the relative direction of the magnetization.