Exchange bias in iron oxide nanoclusters

Abstract

Iron oxide nanoclusters have been prepared by the gas-phase aggregation technique to form thin film structures with very high exchange bias values (up to 3000 Oe at low temperatures). Composition has been analysed by x-ray absorption and Mössbauer spectroscopies in order to elucidate the actual origin of the observed magnetic behaviour. The formation of a metal-oxide core-shell arrangement to explain the observed exchange bias has to be discarded since results show no metallic iron content and the main presence of α-Fe 2 O 3 . The observed weak ferromagnetism and exchange bias are in agreement with the obtained size of α-Fe 2 O 3 nanoparticles: weak ferromagnetism because of the well-known spin canting in this antiferromagnetic structure and exchange bias because of the interaction between different spin sublattice configurations promoted by the modification of iron coordination in α-Fe 2 O 3 nanoparticles. Moreover, the preparation method is proposed for tuning both magnetization and exchange bias values by modification of the preparation conditions of α-Fe 2 O 3 nanoparticles, which open new possibilities in the design of new materials with required properties.

Surface spin disorder and exchange-bias in hollow maghemite nanoparticles

“…[1][2][3][4][5] Several groups have focused on anomalous magnetic behavior in ferrite nanoparticles induced by surface spin disorder such as hysteresis loops exhibiting EB and high field irreversibility. [6][7][8][9][10][11][12][13][14] An explanation for this behavior is that when a large enough fraction of atoms reside at the surface of a particle, the broken exchange bonds are sufficient to induce surface spin disorder thus creating a core-shell structure made of the ferrite core with a shell of disordered spins. 2,6 These disordered spins can take on a number of configurations, one of which can be chosen by field-cooling the particle to induce an EB effect.…”

Influence of Ag nanoparticles on the physical properties of multilayers of graphene

“…Ag nanoparticles (NPs) were deposited by using a sputtering-based cluster source (from Mantis Deposition Ltd.); this equipment is described in [14]. The NPs were deposited at 200 W for 15 and 30 s. These nanoparticles were deposited on graphene after of the transfer process.…”

Evolution of electronic and magnetic properties of nominal magnetite nanoparticles at high pressure probed by x-ray absorption and emission techniques

“…As discussed before, if NPs interacted with silicone oil at ambient and high-pressure conditions, 70% of the volume of the NP would be affected, and spectroscopic features in XANES and XMCD spectra are expected to be significantly affected. We compared the evolution of spectral features in XANES spectra under pressure to see if such evolution could indicate formation of Fe 2 SiO 4 [46], FeH [47], goethite (FeO(OH)) [48], hematite(alpha-Fe 2 O 3 ) [49] and wurtzite (FeO) [49] as a result of reaction with silicon oil. We see no evidence for a sizable contribution from any of these compounds to the XANES spectra.…”