Spin canting across core/shell Fe3O4/MnxFe3−xO4 nanoparticles

Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell Fe3O4/MnxFe3−xO4 MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic correlations, suggesting multiparticle coherent spin canting in an applied field. Atomistic simulations reveal the underlying mechanism of the observed spin canting. These show that strong DMI can lead to magnetic frustration within the shell and cause canting of the net particle moment. These results illuminate how core/shell nanoparticle systems can be engineered for spin canting across the whole of the particle, rather than solely at the surface

X-ray magnetic circular dichroism study of iron/iron oxide granular nanostructures

We present a study of the local magnetic properties of an iron/iron oxide nanostructured granular system by X-ray magnetic circular dichroism. The samples investigated consist of metallic iron (α-Fe) nanoparticles embedded in a nanocrystalline oxide matrix composed by both magnetite (Fe3O4) and maghemite (γ-Fe2O3). Samples were obtained by the inert gas condensation technique. Thanks to the chemical and site selectivity of XMCD, we were able to distinguish the magnetic contributions of the metallic core and of the two oxide phases present in the matrix and independently study their behaviour as a function of iron particle size, applied magnetic field, sample temperature and magnetization history

Local magnetism in granular iron/iron oxide nanostructures: a phase- and site- selective X-ray magnetic circular dichroism study

We present a study of the local magnetic properties of iron/iron oxide granular nanostructures by x-ray magnetic circular dichroism XMCD. Metallic iron -Fe nanoparticles, with average sizes ranging from 5 to 13 nm, are embedded in a nanocrystalline oxide matrix composed of both magnetite Fe3O4 and maghemite -Fe2O3. These granular samples were synthesized by cold compacting core-shell nanoparticles, in which a 2\u20133 nm-thick oxide layer surrounds the iron particles, synthesized by inert gas condensation. By exploiting the chemical selectivity and site sensitivity of XMCD, we were able to separate the magnetic contributions of the metallic core and of the two oxide phases present in the matrix and to study their behavior as a function of iron particle size and applied magnetic induction field. We detected the presence of a significant spin canting, predominantly affecting the octahedral sites of Fe in the oxide phase, and studied its dependence on the degree of structural disorder and applied magnetic induction field

Chill-zone aluminium alloys with GPa strength and good plasticity.

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XMCD Investigation of Spin Disorder in -Fe2O3 Nanoparticles at the Fe L2,3 Edges.

We use XMCD at the L2,3 edges of iron to analyze the site-specific magnetic contributions of ions in nanoparticles of maghemite, -Fe2O3. Maghemite is the oxidized form of magnetite Fe3O4.We report results of the study of the magnetic order on tetrahedral and octahedral magnetic sublattices in -Fe2O3 nanoparticles as a function of the applied magnetic field. Magnetic contributions of Fe3+ Oh and Fe3+ Td are determined using the Ligand Field Multiplet theory. It is found that when the external field decreases, the magnetic contribution of Fe3+ ions on octahedral sites is significantly reduced by comparison to the contribution of Fe3+ ions on tetrahedral ones. This shows that a higher degree of canting exits on octahedral sites

Magnetic order in γ-Fe2O3 nanoparticles: a XMCD study

Spin-canting in spinel nanoparticles of maghemite has multiple origins, among which surface effects, finite-size effects or chemical disorder effects. XMCD at the Fe L2,3 edges allows to separate the contributions of the magnetic moments of Fe3+ ions in tetrahedral and octahedral sites of γ-Fe2O3. We investigate three powders of γ-Fe2O3 synthetized via aqueous precipitation: particles of average diameter 2.7, 8 nm and particles of average diameter 8 nm coated with phosphoric acid. The relative contributions of the spins of the Click to view the MathML source and the Click to view the MathML source ions are observed, varying the external magnetic field. Under high magnetic fields, a reduction of the magnetic contribution of the Click to view the MathML source ions occurs for 8 nm phosphate-coated particles by comparison with the uncoated ones. A similar reduction appears at lower magnetic fields for the small 2.7 nm particles