Magnetism of monomer MnO and heterodimer FePt@MnO nanoparticles

X. Sun (孙笑), A. Klapper, Y. Su (苏夷希), K. Nemkovski, A. Wildes, H. Bauer, O. Köhler, A. Schilmann, W. Tremel, O. Petracic, and Th. Brückel
Phys. Rev. B 95, 134427 – Published 18 April 2017
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Abstract

We report about the magnetic properties of antiferromagnetic (AF) MnO nanoparticles (NPs) with different sizes (6–19 nm). Using a combination of polarized neutron scattering and magnetometry, we were able to resolve previously observed peculiarities. Magnetometry, on the one hand, reveals a peak in the zero-field-cooled (ZFC) magnetization curves at low temperatures (25 K) but no feature around the Néel temperature at 118 K. On the other hand, polarized neutron scattering shows the expected behavior of the AF order parameter vanishing around 118 K. Moreover, hysteresis curves measured at various temperatures reveal an exchange-bias effect, indicating a coupling of an AF core to a ferromagnetic (FM)-like shell. ZFC data measured at various fields exclude a purely superparamagnetic (SPM) scenario. We conclude that the magnetic behavior of MnO particles can be explained by a superposition of SPM-like thermal fluctuations of the AF-Néel vector inside the AF core and a magnetic coupling to a ferrimagnetic Mn2O3 or Mn3O4 shell. In addition, we have studied heterodimer (“Janus”) particles, where a FM FePt particle is attached to the AF MnO particle. Via the exchange-bias effect, the magnetic moment of the FePt subunit is stabilized by the MnO.

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  • Received 25 September 2016
  • Revised 13 February 2017

DOI:https://doi.org/10.1103/PhysRevB.95.134427

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

X. Sun (孙笑)1, A. Klapper1, Y. Su (苏夷希)2, K. Nemkovski2, A. Wildes3, H. Bauer4, O. Köhler4, A. Schilmann4, W. Tremel4, O. Petracic1, and Th. Brückel1

  • 1Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
  • 2Jülich Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum MLZ, Forschungszentrum Jülich GmbH, 85747 Garching, Germany
  • 3Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9, France
  • 4Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany

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Issue

Vol. 95, Iss. 13 — 1 April 2017

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