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International audienceX-ray magnetic circular dichroism (XMCD) experiments were carried out to compare the Fe2+/ Fe3+ ratio in nanomagnetite chemically produced from lepidocrocite and nanomagnetite biogenically produced by the Fe-reducing bacterium Shewanella putrefaciens. Together with TEM imaging, these measurements showed that the biotic magnetite nanoparticles were of excellent quality, with small size dispersion and high crystallinity. From the XMCD measurements, it could be shown that the biogenic nanomagnetite contained a higher amount of Fe2+ than the abiogenic nanomagnetite

We present a study of the local magnetic properties of iron/iron oxide granular nanostructures by x-ray magnetic circular dichroism ͑XMCD͒. Metallic iron ͑␣-Fe͒ nanoparticles, with average sizes ranging from 5 to 13 nm, are embedded in a nanocrystalline oxide matrix composed of both magnetite ͑Fe 3 O 4 ͒ and maghemite ͑␥-Fe 2 O 3 ͒. These granular samples were synthesized by cold compacting core-shell nanoparticles, in which a 2 -3 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.

Using a cold graphite mold casting method, bulk AlNiY chill-zone alloys were prepared at hypereutectic compositions with Al content from 85 at.% to 94 at.%. It was found that ultra-hard surface layers with a thickness of about 200 μm and submicron grain size form when the melt can be undercooled without heterogeneous nucleation at the mold contact surface. This hard chill-zone forming in contact with the mold possesses Vickers microhardness Hv about 350–420 and is thus harder than fully amorphous Al alloys. In compression, ultimate strength more than 1.1 GPa and true strain more than 150% without failure were achieved simultaneously. The combination of high strength and good plasticity will be discussed in relation to the special structure of the chill-zone alloy.

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