Transports in granular structures

Abstract

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.

Date of Award	2001
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology