Conditions for optimum giant magnetoresistance in granular metals

The dependence of the giant magnetoresistance (GMR) of a metallic granular system on the concentration of magnetic particles is studied numerically. T he effect of particle coalescence and dipolar interactions between the part icles on the value of optimum GMR and the shape of the concentration depend ence curve are discussed. The micromagnetic configuration of the system is obtained by a Monte Carlo algorithm that involves short-range effective exc hange couplings and long range dipolar interactions. The conductivity is ob tained using Kubo's formula for a tight binding Hamiltonian. A comparison o f our results to experiments on metallic granular films is made. (C) 2001 A merican Institute of Physics.