Nonlinear dynamic susceptibilities of interacting and noninteracting magnetic nanoparticles

The linear and cubic dynamic susceptibilities of solid dispersions of nanos ized maghemite gamma -Fe2O3 particles have been measured for three samples with a volume concentration of magnetic particles ranging from 0.3% to 17%, in order to study the effect of dipole-dipole interactions. Significant di fferences between the dynamic response of the samples are observed. While t he linear and cubic dynamic susceptibilities of the most dilute sample comp are reasonably well with the corresponding expressions proposed by Raikher and Stepanov for noninteracting particles, the nonlinear dynamic response o f the most concentrated sample exhibits at low temperatures similar feature s as observed in a Ag(11 at% Mn) spin glass. (C) 2000 Elsevier Science B.V. All rights reserved.