Superparamagnetic nanoparticle ensembles

Magnetic single-domain nanoparticles constitute an important model system in magnetism. In particular, ensembles of superparamagnetic nanoparticles can exhibit a rich variety of different behaviors depending on the inter-particle interactions. Starting from isolated single-domain ferromagnetic or ferrimagnetic nanoparticles, the magnetization behavior of both non-interacting and interacting particle ensembles is reviewed. Particular attention is given to the relaxation time of the system. In the case of interacting nanoparticles the usual Néel–Brown relaxation law becomes modified. With increasing interactions, modified superparamagnetism, spin glass behavior and superferromagnetism are encountered.