Magnetic phase transitions in nanoclusters and nanostructures

Abstract

Theoretical models and experimental data on magnetic phase transitions in magnetic nanoclusters and nanostructures were reviewed. It was shown that nanoclusters measuring from several nanometers to several tens of nanometers possess a critical size (which can be likened to the critical Curie or Neel temperatures). At undercritical cluster sizes the magnetic order in cluster and cluster nanostructure vanishes by first-order magnetic phase transitions (abruptly). In this context, a change-over from the first- to second-order magnetic phase transition, a decrease or increase in the Neel and Curie temperatures, and critical nanocluster size calculations were accomplished for a number of nanoobjects. These include ferric oxides and hydroxides in matrix nanostructures comprised of isolated nanoclusters, as well as in nanostructures including strongly interacting or organized clusters and in nanostructures induced by shear stress under high pressure loading.