The universal theory of critical phase transitions describes the critical behavior at second-order phase transitions in infinitely large systems. With the increased contemporary interest in nanoscale materials, we investigated CoO nanoparticles by means of neutron scattering and found how the theory of critical phenomena breaks down in the nanoscale regime. Using CoO as a model system, we have identified a size-dependent nanocritical temperature region close to the antiferromagnetic phase transition where the magnetic correlation length of the nanoparticles converges to a constant value, which is significantly smaller than that of the saturated state found at low temperatures. This is in clear contrast to the divergence around TN observed for bulk systems. Our findings of nanocriticality in the magnetic phase transition is of great importance for the understanding of phase transitions at the nanoscale.
@article{arxiv.2205.13975,
title = {Nanocriticality in the magnetic phase transition of CoO nanoparticles},
author = {Machteld E. Kamminga and Jonas Okkels Birk and Jari í Hjøllum and Henrik Jacobsen and Jakob Lass and Thorbjørn L. Koch and Niels B. Christensen and Christof Niedermayer and Lukas Keller and Luise Theil Kuhn and Elisabeth T. Ulrikkeholm and Erik Brok and Cathrine Frandsen and Kim Lefmann},
journal= {arXiv preprint arXiv:2205.13975},
year = {2023}
}