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.

Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties

“…29 These values are typical and have been confirmed on similar samples by transmission electron microscopy (TEM). 36 In this sample after irradiation (S2-i), the Fe core shrinks slightly to 7 nm but the shell transformed to FeO with crystallite size 13 nm, as determined by whole pattern fitting. As seen by TEM ( Figure 4, discussed below), this crystallite size is no longer just the shell thickness but represents the FeO matrix between two Fe cores.…”

Single-step gas phase synthesis of stable iron aluminide nanoparticles with soft magnetic properties

“…Iron aluminide nanoparticles of 10.8 nm (±2.5 nm) display a high saturation magnetization (Ms) of 204 emu g −1 at 10 K and 170 emu g −1 at 300 K. This value of Ms is among the highest value reported so far for iron aluminide materials [18][19][20] and is much higher than that of iron oxide with similar size (typical range from 70 to 110 emu g −1 ). 21,22 Interestingly, our iron aluminide nanoparticles display a high stability against oxidation (Figure 4, inset) compared to other iron-based nanoparticles reported in literature. 23,24 The low value below 0.5 (non-interacting particles) of the remanence ratio Mr/Ms could be explained simply by the effect of competition between the inter-and intra-particle interaction on the spin relaxation process 25 and as a result of the encapsulation by the alumina shell, which provides weak inter-particles interactions.…”

Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

“…3(a)-3(d), indicating the establishment of exchange bias. 2,22 The local coercivity H C increased substantially from the room temperature value [ Fig. 3(e)].…”