Size dependence of inter- and intracluster interactions in core-shell iron-iron oxide nanoclusters

Abstract

The room-temperature magnetic properties of core-shell iron-iron oxide nanoclusters (NCs) synthesized by a cluster deposition system were investigated, and their dependence on mean cluster size is discussed. In this study, the surface/boundary spins of clusters were not frozen and were thermally activated during the measurements. The intercluster interactions between clusters and intracluster interactions between the iron core (ferromagnetic) and iron oxide shell (ferrimagnetic) were investigated by field-dependent isothermal remanent magnetization and dc demagnetization measurements at room temperature. The Henkel and ΔM plots support the existence of dipolar intercluster interactions that become stronger with the growth of the clusters. The derivative of the initial magnetization curve implies that smaller clusters require lower fields and less time than larger ones to overcome various energy barriers before saturating the moments along the field direction. Coercive field and magnetization were also correlated with the interaction parameters. To compare the room-temperature magnetic results, one system was studied at low temperature, where exchange coupling at the interface between the oxide and metallic phases was observed through bias effect and anisotropy enhancement. © 2012 American Chemical Society.