Evaluation of interparticle interactions between magnetic nanoparticles using first order reversal curves and Weiss temperature

Two conventional methods for evaluating interparticle magnetic interactions are applied to magnetic nanoparticle assemblies with various interparticle distances that are controlled by a silica coating. According to Weiss temperatures derived from superparamagnetic response analysis, the mean values of the interparticle magnetic interactions are relatively small and seem to be independent of the interparticle distance. The interaction fields in the first-order reversal curve diagram for narrow interparticle distances are widely distributed. However, the interaction fields disappear when the interparticle distance is sufficiently large. Analysis of these two contrasting results indicates that ferromagnetic-like and antiferromagnetic-like magnetic couplings coexist and cancel each other, as in atomic spin glasses.