Bi-domain state in the exchange bias system FeF2/Ni

TL;DR

This paper investigates the coexistence of exchange-biased subsystems in FeF2/Ni bilayers, revealing a bi-domain state with independent magnetic subsystems that influence the ferromagnet differently, supported by experiments and micromagnetic simulations.

Contribution

It introduces the concept of a bi-domain state in exchange bias systems and demonstrates its existence through experiments and simulations, a novel insight into magnetic coupling.

Findings

Double hysteresis loops at intermediate cooling fields.

Antiferromagnet breaks into two subsystems with opposite bias signs.

Thermally activated motion of antiferromagnetic domain boundaries.

Abstract

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