Instability of exchange bias induced by an overlaid superconductor tab in antiferromagnet\ferromagnet bilayers

The effect of a superconducting overlaid layer on exchange bias in antiferromagnet/ferromagnet bilayers is investigated through temperature-dependent electrical transport measurements. It is found that below the transition temperature of the superconductor, the exchange bias field (H-e) and coercivity (H-c) of the bilayer vary randomly in repeated magnetoresistance measurements, while they remain as constant above the superconductor transition temperature. We attribute this to the instability of spin structure of the antiferromagnet induced by the superconductor, which in turn affects the exchange bias at the antiferromagnet/ferromagnet interface. Micromagnetic modeling is performed to assist the interpretation of the experimental results. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729031]