Europhys. Lett.
Volume 48, Number 5, December 1999
Page(s) 573 - 579
Section Condensed matter: electronic structure, electrical, magnetic and optical properties
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00522-9

Europhys. Lett, 48 (5), pp. 573-579 (1999)

Exchange bias model for Fe/FeF$_{\rm 2}$: Role of domains in the ferromagnet

M. Kiwi, J. Mejía-López, R. D. Portugal and R. Ramírez

Facultad de Física, Pontificia Universidad Católica - Casilla 306, Santiago 22, Chile

(received 5 July 1999; accepted in final form 6 October 1999)

PACS. 75.70$\rm -i$ - Magnetic films and multilayers.
PACS. 75.70Cn - Interfacial magnetic properties (multilayers, magnetic quantum wells, superlattices, magnetic heterostructures).
PACS. 75.60Ej - Magnetization curves, hysteresis, Barkhausen and related effects.


Exchange bias (EB) is a shift of the hysteresis loop from its normal position, symmetric around H=0, to $H_{\rm E}\ne 0$. It occurs when thin ferromagnetic (F) films are deposited on a variety of antiferromagnetic (AF) materials. EB is also associated with several additional remarkable features: i) the bulk magnetizations of the F is orthogonal to the AF easy axis; ii) $H_{\rm E}$ is of similar magnitude for compensated and uncompensated AF interface layers; iii) the sign of $H_{\rm E}$ can assume both positive and negative values; and, iv) the magnetization $\vert M(H \ll - H_{\rm c})\vert \neq \vert M(H \gg + H_{\rm c})\vert \
$, where $H_{\rm c}$ is the coercive field. Here we propose a model that describes the EB phenomenon for a compensated interface. Based on the experimental evidence, and extensive computer simulations, we suggest that close to the Néel temperature a canted spin configuration in the AF interface freezes into a metastable state. As a consequence, the EB energy is reversibly stored in a spring-like magnet, or incomplete domain wall (IDW), in the F slab. The results we extract from our model, both analytically and through simulations, are qualitatively and quantitatively compatible with the available experimental information.


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