We discuss the electronic transport properties of a two dimensional granular magnetic composite numerically. The composite consists of ferromagnetic metallic nano-sized grains distributed randomly on a non-magnetic, insulating medium. The grains are not touching one another but electrons can hop between them, so the bulk resistance is a function of temperature and particle size. It is also a function of magnetic field because of the spin-dependent scattering of electrons when they travel between the magnetic grains. This introduces a magnetoresistance into the network....[ Read more ]

We discuss the electronic transport properties of a two dimensional granular magnetic composite numerically. The composite consists of ferromagnetic metallic nano-sized grains distributed randomly on a non-magnetic, insulating medium. The grains are not touching one another but electrons can hop between them, so the bulk resistance is a function of temperature and particle size. It is also a function of magnetic field because of the spin-dependent scattering of electrons when they travel between the magnetic grains. This introduces a magnetoresistance into the network.

For simplicity, we assume that the grains are located on a regular square lattice so that we can treat the composite as a classical random resistor network (RRN). The occupancy of the sites is controlled by the concentration of the grains. The bond conductance between every two sites is assigned as a function of temperature and the size of the two grains involved according to the hopping model. The effect of magnetic field is introduced using Gittleman’s model of magnetoresistance. Finally, a potential difference is applied across the network, and the bulk resistance of the network is calculated numerically using successive over-relaxation (SOR). In this way we have investigated the dependence of this bulk resistance on temperature, magnetic field and particle size distributions. The results are compared with experiments whenever possible.