We report on the low-temperature magnetic ac-susceptibility of antiferromagnetic DyPO4 nanoparticles with a very high surface to volume ratio. The results are interpreted in terms of superparamagnetic relaxation of the Neel vector arising from a relatively large number approx 0.2 Na of uncompensated spins probably existing on the surface of the nanoparticles. The activation energy of the relaxation process is found to be Ea / kB = (2.6+-0.1) K within a model taking into account the magnetic interaction between nanoparticles.
@article{arxiv.cond-mat/0304016,
title = {Superparamagnetic behaviour of antiferromagnetic DyPO4 nanoparticles},
author = {T. G. Sorop and M. Evangelisti and M. Haase and L. J. de Jongh},
journal= {arXiv preprint arXiv:cond-mat/0304016},
year = {2007}
}