Issue
EPL
Volume 88, Number 5, December 2009
Article Number 57004
Number of page(s) 4
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/88/57004
Published online 11 December 2009
EPL, 88 (2009) 57004
DOI: 10.1209/0295-5075/88/57004

On beating the superparamagnetic limit with exchange bias

R. F. L. Evans1, R. Yanes2, O. Mryasov3, R. W. Chantrell1 and O. Chubykalo-Fesenko2

1   Department of Physics, University of York - York, YO10 5DD, UK, EU
2   Instituto de Ciencia de Materiales de Madrid, CSIC - Cantoblanco, 28049 Madrid, Spain, EU
3   Center for Materials and Information Technology, University of Alabama - Tuscaloosa, AL, USA

rfle500@york.ac.uk

received 2 September 2009; accepted in final form 12 November 2009; published December 2009
published online 11 December 2009

Abstract
In order to investigate the possibility of “beating the superparamagnetic limit with exchange bias” (SKUMRYEV V. et al., Nature423 (2003) 19) we perform atomistic modeling on Co/CoO magnetic nanoparticles varying the strength of the ferromagnet/antiferromagnet interfacial coupling. Our results show that exchange-biased systems exhibit an increased energy barrier along the bias direction, with a corresponding decrease of the barrier in the opposite direction. For systems with large values of the interfacial coupling, the ferromagnetic core is found to be unconditionally stable in the bias direction. Such a system is ideal for thermal stability since there is no energetically stable reversed state, providing the antiferromagnetic shell is unchanged. In order to permit magnetic recording, which essentially requires a bi-stable system, we propose a heat-assisted recording method, whereby both the ferromagnet (FM) and antiferromagnet (AF) are switched. Upon heating to the Néel temperature of CoO, the AF magnetic order is destroyed allowing switching of the FM core with a small applied field, with thermal stability reappearing on cooling through TN.

PACS
75.75.+a - Magnetic properties of nanostructures.
75.10.Hk - Classical spin models.
75.50.Tt - Fine-particle systems; nanocrystalline materials.

© EPLA 2009