Giant magnetoresistance in a three-dimensional lattice of dipolar interacting magnetic nanoparticles

The magnetization and the giant magnetoresistance (GMR) of three-dimensional multilayered lattice of dipolar interacting fine anisotropic magnetic particles embedded in a nonmagnetic metallic matrix are numerically investigated. Using a Monte Carlo method the dependence of the magnetization curve and the GMR effect on the magnetic field H, temperature, the number of layers, the magnetic anisotropy, the separation between neighboring particles, and the particle-size distribution are examined systematically. We found that the enhanced dipolar interaction at high particle densities and for wide particle-size distributions reveals itself as a substantial suppression in the change in the negative MR with the applied field H. For out-of-plane magnetic field orientation, the negative MR is shown to increase more rapidly with H as the number of layers increases. This effect is attributed to the demagnetization field arising from the free magnetic poles forming at the sample surface. The relevance of the present results to the understanding of the magnetic and transport properties in granular composites is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.