Dipolar-coupled moment correlations in clusters of magnetic nanoparticles

Research output: Contribution to journalJournal article – Annual report year: 2019Researchpeer-review



  • Author: Bender, P.

    University of Cantabria, Spain

  • Author: Wetterskog, E.

    Uppsala University, Sweden

  • Author: Honecker, D.

    Institut Laue-Langevin, France

  • Author: Fock, Jeppe

    Technical University of Denmark, Denmark

  • Author: Frandsen, C.

    Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark, Fysikvej, 2800, Kgs. Lyngby, Denmark

  • Author: Moerland, C.

    Eindhoven University of Technology, Netherlands

  • Author: Bogart, Lara K.

    University College London, United Kingdom

  • Author: Posth, O.

    Physikalisch-Technische Bundesanstalt, Germany

  • Author: Szczerba, W.

    Bundesanstalt für Materialforschung und Prüfung, Germany

  • Author: Gavilán, H.

    Instituto de Ciencia de Materiales de Madrid, Spain

  • Author: Costo, Rocio

    Instituto de Ciencia de Materiales de Madrid, Spain

  • Author: Fernández-Díaz, M. T.

    Institut Laue-Langevin, France

  • Author: González-Alonso, D.

    University of Cantabria, Spain

  • Author: Fernandez Barquin, L.

    University of Cantabria, Spain

  • Author: Johansson, C

    RISE Acreo AB, Sweden

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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 Mossbauer 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.
Original languageEnglish
Article number224420
JournalPhysical Review B
Issue number22
Number of pages11
Publication statusPublished - 2018
CitationsWeb of Science® Times Cited: No match on DOI

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