Fast laser annealing induced exchange bias in poly-crystalline BiFeO₃/Co bilayers

Graphical abstract: - Highlights: • Fast laser annealing can modify the exchange bias in BiFeO₃/Co bilayers. • The mechanism replies on much less interfacial diffusion during laser annealing. • Proper laser fluence activates the interfacial spins to align with the cooling field. • Exchange bias can be locally induced in BiFeO₃/FM bilayer in micrometer size. - Abstract: The conventional field cooling process for antiferromagnetic/ferromagnetic bilayer system might strongly damage the interface of BiFeO₃ (BFO) with metallic ferromagnetic layer, leading to significant deterioration of exchange bias (EB). In this paper, a field cooling process with fast laser annealing has been proposed and applied on polycrystalline-BFO/Co bilayers, which can effectively modify the EB. In those samples with obvious EB, it is found that the exchange field (H_E) increases abruptly when the laser fluence rises to a critical value, and decreases when the laser fluence is large enough. On the other hand, in those samples with negligible H_E, EB could be easily induced after field cooling with proper laser fluence. In addition, the sign of H_E could also be changed, depending on the direction of the cooling field. In contrast, after field cooling by conventional heat treatment, EB could be neither induced nor enhanced. The feasibility of fast laser annealing accompanied with field cooling to enhance or induce EB in the BFO/Co bilayer can be understood by much less interfacial diffusion in comparison with conventional field cooling.