Investigation of the magnetic susceptibility of nanocomposites obtained in zero-field-cooled conditions

An investigation of the effect of particle size, size dispersion, intensity of applied field, and anisotropy constant on the characteristics of the superparamagnetism of magnetic nanocomposites was carried out using an integral equation for the magnetic susceptibility that assumes uniaxial anisotropy. The nanoscopic phase of the composites is composed of noninteracting randomly oriented single-domain spheres embedded in a nonmagnetic host. A Gaussian distribution for the particle diameter dispersion was used in agreement with experimental results. The results show that the above parameters alter the position and width of the superparamagnetic peak, but only particle size and size dispersion can affect the shape of the high-temperature susceptibility tail above the peak temperature. Higher size dispersion values lead to broader peaks shifted to higher temperatures and flatter high-temperature tails. Simulations of experimental data obtained from cobalt nanocomposites, where the average particle size and size distribution were previously determined by transmission electron microscopy, yielded very good agreement. (c) 2006 American Vacuum Society.