High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect

José A. De Toro, Daniel P. Marques, Pablo Muñiz, Vassil Skumryev, Jordi Sort, Dominique Givord, and Josep Nogués
Phys. Rev. Lett. 115, 057201 – Published 28 July 2015
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Abstract

Thermal activation tends to destroy the magnetic stability of small magnetic nanoparticles, with crucial implications for ultrahigh density recording among other applications. Here we demonstrate that low-blocking-temperature ferromagnetic (FM) Co nanoparticles (TB<70K) become magnetically stable above 400 K when embedded in a high-Néel-temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable TB enhancement is due to a magnetic proximity effect between a thin CoO shell (with low Néel temperature, TN, and high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix (with high TN but low KAFM). This proximity effect yields an effective antiferromagnet with an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations via core-shell exchange-bias coupling, leading to the observed TB increase. Mean-field calculations provide a semiquantitative understanding of this magnetic-proximity stabilization mechanism.

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  • Received 3 February 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.057201

© 2015 American Physical Society

Authors & Affiliations

José A. De Toro1,*, Daniel P. Marques1, Pablo Muñiz1, Vassil Skumryev2,3, Jordi Sort2,3, Dominique Givord4,5,6,†, and Josep Nogués3,7,‡

  • 1Instituto Regional de Investigación Científica Aplicada (IRICA) and Departamento de Física Aplicada, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain
  • 2Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
  • 3Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
  • 4Université Grenoble Alpes, Institut NEEL, F-38042 Grenoble, France
  • 5CNRS, Institut NEEL, F-38042 Grenoble, France
  • 6Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, 21941-972, Brasil
  • 7ICN2–Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, E-08193 Bellaterra, Barcelona, Spain

  • *JoseAngel.Toro@uclm.es
  • Dominique.Givord@neel.cnrs.fr
  • Josep.Nogues@uab.cat

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Issue

Vol. 115, Iss. 5 — 31 July 2015

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