Microscopic model for exchange bias from grain-boundary disorder in a ferromagnet/antiferromagnet thin film with a nanocrystalline microstructure

Monte Carlo spin simulations were coupled to a Voronoi microstructure-generator to predict the magnitude and behavior of exchange bias in a ferromagnet/antiferromagnet (AF) thin film bilayer with a nanocrystalline microstructure. Our model accounts for the effects of irregular grain-shapes, finite-s...

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Veröffentlicht in:Applied physics letters 2014-07, Vol.105 (3)
Hauptverfasser: Cortie, D. L., Biternas, A. G., Chantrell, R. W., Wang, X. L., Klose, F.
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Sprache:eng
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Zusammenfassung:Monte Carlo spin simulations were coupled to a Voronoi microstructure-generator to predict the magnitude and behavior of exchange bias in a ferromagnet/antiferromagnet (AF) thin film bilayer with a nanocrystalline microstructure. Our model accounts for the effects of irregular grain-shapes, finite-sized particles, and the possible presence of local random-fields originating from the antiferromagnet's grain-boundary regions. As the grain-boundary represents a crystal-structure distortion, we model the local effect on the exchange constants in the Gaussian approximation which can cause regions resembling a spin glass confined to an unusual 2D topology. Although an ensemble of completely disconnected AF grains isolated by non-magnetic barriers provides a small exchange bias, the introduction of a spin-glass network at the boundaries causes a four-fold enhancement in the magnitude of the loop-shift. This implies the importance of local grain-boundary behavior in defect-engineered antiferromagnets.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.4890580