We have studied the magnetic behavior of dextran-coated magnetite (Fe3O4) nanoparticles with median particle size ⟨d⟩=8nm. Magnetization curves and in-field M\"ossbauer spectroscopy measurements showed that the magnetic moment MS of the particles was much smaller than the bulk material. However, we found no evidence of magnetic irreversibility or non-saturating behavior at high fields, usually associated to spin canting. The values of magnetic anisotropy Keff from different techniques indicate that surface or shape contributions are negligible. It is proposed that these particles have bulk-like ferrimagnetic structure with ordered A and B sublattices, but nearly compensated magnetic moments. The dependence of the blocking temperature with frequency and applied fields, TB(H,ω), suggests that the observed non-monotonic behavior is governed by the strength of interparticle interactions.
@article{arxiv.cond-mat/0505682,
title = {Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles},
author = {E. Lima and A. L. Brandl and A. D. Arelaro and G. F. Goya},
journal= {arXiv preprint arXiv:cond-mat/0505682},
year = {2007}
}