Magnetism of iron oxide based core-shell nanoparticles from interface mixing with enhanced spin-orbit coupling

E. Skoropata, R. D. Desautels, C.-C. Chi, H. Ouyang, J. W. Freeland, and J. van Lierop
Phys. Rev. B 89, 024410 – Published 13 January 2014

Abstract

We show that the magnetism of core-shell nanoparticles (made of maghemite, γ-Fe2O3, cores and transition-metal and metal-oxide shells) is altered substantially by the interface, which is a doped iron-oxide layer formed naturally during the seed-mediated synthesis process, a route used typically to produce core-shell nanoparticles. Characteristics fundamental to useful applications, such as the anisotropy and superparamagnetic blocking temperature, were altered substantially with Cu, CoO, MnO, and NiO shells. To ascertain the origin of this behavior, the prototype γ-Fe2O3/CoO core-shell nanoparticles are described in detail. We show that the magnetism originates essentially from an interfacial doped iron-oxide layer formed via migration of shell ions, e.g., Co2+, into octahedral site vacancies in the surface layers of the γ-Fe2O3 core. For this system, an overall Fe morb/mspin=0.15±0.03 is measured (morb0 for the Fe-oxides) and an enhanced Co morb/mspin=0.65±0.03 elucidates the origin of the unexpectedly high overall anisotropy of the nanoparticle. This interfacial layer is responsible for the overall (e.g., bulk) magnetism and provides a perspective on how the magnetism of core-shell nanoparticles manifests from the selected core and shell materials.

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  • Received 14 August 2013
  • Revised 28 November 2013

DOI:https://doi.org/10.1103/PhysRevB.89.024410

©2014 American Physical Society

Authors & Affiliations

E. Skoropata1,*, R. D. Desautels1, C.-C. Chi2, H. Ouyang2, J. W. Freeland3, and J. van Lierop1,†

  • 1Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
  • 2Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan
  • 3Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

  • *eskoropata@physics.umanitoba.ca
  • Johan.van.Lierop@umanitoba.ca

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Vol. 89, Iss. 2 — 1 January 2014

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