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Dipolar-coupled moment correlations in clusters of magnetic nanoparticles
University of Cantabria, Spain.
Uppsala University, Sweden.
Institut Laue-Langevin, France.
DTU Technical University of Denmark,, Denmark.
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 22, article id 224420Article in journal (Refereed) Published
Abstract [en]

Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid-coated magnetic nanoparticles. The individual iron oxide cores were composed of >95% maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent ac susceptibility data in the superparamagnetic regime indicates a tendency for dipolar-coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross section. The correlation function suggests nonstochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core clusters.

Place, publisher, year, edition, pages
2018. Vol. 98, no 22, article id 224420
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-37023DOI: 10.1103/PhysRevB.98.224420Scopus ID: 2-s2.0-85058959420OAI: oai:DiVA.org:ri-37023DiVA, id: diva2:1280056
Note

 Funding details: Danmarks Frie Forskningsfond, DFF; Funding details: 604448;

Available from: 2019-01-17 Created: 2019-01-17 Last updated: 2019-06-27Bibliographically approved

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