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Applied Physics Letters / Volume 87 / Issue 1 / MAGNETISM AND SUPERCONDUCTIVITY

Appl. Phys. Lett. 87, 012501 (2005); http://dx.doi.org/10.1063/1.1978977 (3 pages)

Critical size for exchange bias in ferromagnetic-antiferromagnetic particles

A. N. Dobrynin1, D. N. Ievlev1, K. Temst1, P. Lievens1, J. Margueritat2, J. Gonzalo2, C. N. Afonso2, S. Q. Zhou3, A. Vantomme3, E. Piscopiello4, and G. Van Tendeloo4

1Laboratorium voor Vaste-Stoffysica en Magnetisme, K.U.Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
2Instituto de Optica, CSIC, Serrano 121, 28006 Madrid, Spain
3Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
4Elektronenmicroscopie voor Materiaalonderzoek, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerp, Belgium

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(Received 28 February 2005; accepted 23 May 2005; published online 27 June 2005)

We present a study of the magnetic properties of oxidized Co nanoparticles with an average grain size of 3 nm, embedded in an amorphous Al2O3 matrix. These nanoparticles can be considered as imperfect Co-core CoO-shell systems. Magnetization measurements after magnetic field cooling show a vertical shift of the hysteresis loop, while no exchange bias is observed. With a simple model, we show that there is a critical grain size for hybrid ferromagnetic-antiferromagnetic particles, below which exchange bias is absent for any ratio of ferromagnetic and antiferromagnetic constituents. The reason is that the interfacial exchange energy dominates over other energies in the system due to a large surface-to-volume ratio in the nanoparticles.

© 2005 American Institute of Physics

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KEYWORDS and PACS

Keywords

ferromagnetic materials, antiferromagnetic materials, cobalt, nanoparticles, grain size, amorphous state, aluminium compounds, magnetic cooling, magnetic hysteresis, surface energy, exchange interactions (electron), magnetic particles

PACS

  • 75.50.Tt

    Fine-particle systems; nanocrystalline materials

  • 75.50.Cc

    Other ferromagnetic metals and alloys

  • 75.50.Ee

    Antiferromagnetics

  • 75.60.Ej

    Magnetization curves, hysteresis, Barkhausen and related effects

  • 75.30.Sg

    Magnetocaloric effect, magnetic cooling

  • 75.30.Et

    Exchange and superexchange interactions

  • 61.46.-w

    Structure of nanoscale materials

  • 68.35.Md

    Surface thermodynamics, surface energies

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.1978977

PUBLICATION DATA

ISSN

0003-6951 (print)  
1077-3118 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
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