Effect of interparticle interactions and size dispersion in magnetic nanoparticle assemblies: A static and dynamic study

Abstract

Interparticle interactions in magnetic nanoparticles are studied by dc and ac magnetization measurements. For non-interacting nanoparticles, while the anisotropy constant of the nanoparticles K-eff = 1.6 x 10(5) erg/cm(3) is accurately determined by fitting zero-field-cooled and field-cooled measurements, we show that K-eff values deduced only from time relaxation measurements must require simultaneous adjustments of the complex susceptibility by taking into account the size distribution of nanoparticles. This leads to K-eff 1.7 x 10(5) erg/cm(3) in agreement with dc measurements. For interacting nanoparticles, comparisons with theoretical models show that energies due to magnetic dipolar interactions can only be predicted for weak and moderate interactions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624833]