Exchange bias effect of Co3−xFexO4 (x = 0, 0.09, 0.14 and 0.27)

Co3−xFexO4 (x = 0, 0.09, 0.14 and 0.27) powders were synthesized by the thermal-decomposition method with annealing treatment. With the increase of x, the composition of the products experiences a transition from the single-phase compound of Co3−xFexO4 to the coexisted phases of Co3−xFexO4 and CoFe2O4, which is accompanied with the enhancement of the ferromagnetic (FM) response. In addition, the horizontal negative exchange bias (EB) effect was observed in the Fe3+ doped samples. For Co3−xFexO4 with x = 0.09 and 0.14, the EB fields at 10 K are larger than 100 Oe, and the EB effect disappears as temperature is above 30 K, close to the Néel temperature for the antiferromagnetic (AFM) Co3O4. While for Co3−xFexO4 with x = 0.27, the EB field at 10 K weakens clearly, but the EB effect finally disappears as temperature increases to 200 K. These results indicate that the EB effect for Co3−xFexO4 with x = 0.09 and 0.14 are mainly related with the exchange coupling at the FM/AFM interfaces, while for x = 0.27, the decoupling of the FM and AFM phases may occur.

► Co3−xFexO4 (x = 0, 0.09, 0.14 and 0.27) powders were synthesized by the thermal-decomposition. ► The enhancement of the ferromagnetic (FM) response was observed with the increase of x. ► The horizontal negative exchange bias (EB) effect was observed in the Fe3+ doped samples. ► For x = 0.09 and 0.14, the EB effect is due to the coupling at the FM/AFM interfaces. ► For x = 0.27, the coupling between the FM/AFM interfaces is destroyed.