Effects of dipole-dipole interactions on the magnetic relaxation have been investigated for three Fe-C nanoparticle samples with volume concentrations of 0.06, 5 and 17 vol%. While both the 5 and 17 vol% samples exhibit collective behavior due to dipolar interactions, only the 17 vol% sample displays critical behavior close to its transition temperature. The behaviour of the 5 vol% sample can be attributed to a mixture of collective and single particle dynamics.
@article{arxiv.cond-mat/0010090,
title = {Critical dynamics of an interacting magnetic nanoparticle system},
author = {M. F. Hansen and P. Jönsson and P. Nordblad and P. Svedlindh},
journal= {arXiv preprint arXiv:cond-mat/0010090},
year = {2009}
}