Bidomain state in exchange biased FeF2∕Ni

Independently exchange biased subsystems can coexist in FeF2/Ni bilayersafter various field-cooling protocols. We find double hysteresis loops forintermediate cooling fields, while for small or large cooling fields anegatively or positively shifted single loop, respectively, are encountered.Both the subloops and the single loops have the same absolute value of theexchange bias field, mu_0 H_E = 0.09 T. This suggests that the antiferromagnetbreaks into two magnetic subsystems with opposite signs but equal magnitude ofbias acting on the ferromagnet. In this case the ferromagnet does notexperience an average bias from the antiferromagnet but rather two independentsubsystems ('bi-domain' state). This idea is confirmed by micromagneticsimulations including the effect of the antiferromagnet. We also presentexperiments, where thermally activated motion of these antiferromagnetic'domain' boundaries can be achieved