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The magnetic structure factor of correlated nanoparticle moments in small-angle neutron scattering

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      Abstract

      Here, we derive expressions for the magnetic small-angle neutron scattering (SANS) cross section of magnetic nanoparticle ensembles under consideration of a magnetic structure factor. We show that for structurally disordered ensembles with correlated particle moments the magnetic structure factor is in general (i) anisotropic also in zero field, and (ii) that in saturation the magnetic structure factor deviates from the nuclear one. These theoretical predictions allow to explain our experimental, polarized SANS data of an ensemble of weakly interacting iron oxide nanoparticles.

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      Configuration of the magnetosome chain: a natural magnetic nanoarchitecture

      Magnetospirillum gryphiswaldense is a microorganism with the ability to biomineralize magnetite nanoparticles, called magnetosomes, and arrange them into a chain that behaves like a magnetic compass. Magnetospirillum gryphiswaldense is a microorganism with the ability to biomineralize magnetite nanoparticles, called magnetosomes, and arrange them into a chain that behaves like a magnetic compass. Rather than straight lines, magnetosome chains are slightly bent, as evidenced by electron cryotomography. Our experimental and theoretical results suggest that due to the competition between the magnetocrystalline and shape anisotropies, the effective magnetic moment of individual magnetosomes is tilted out of the [111] crystallographic easy axis of magnetite. This tilt does not affect the direction of the chain net magnetic moment, which remains along the [111] axis, but explains the arrangement of magnetosomes in helical-like shaped chains. Indeed, we demonstrate that the chain shape can be reproduced by considering an interplay between the magnetic dipolar interactions between magnetosomes, ruled by the orientation of the magnetosome magnetic moment, and a lipid/protein-based mechanism, modeled as an elastic recovery force exerted on the magnetosomes.
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        Dewhurst Wynford

        (2011)
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          Author and article information

          Journal
          12 April 2019
          1904.06243

          http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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          cond-mat.mes-hall

          Nanophysics

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