Exchange bias effect of Co 3− xFe xO 4 ( x = 0, 0.09, 0.14 and 0.27)

Abstract

Co 3− x Fe x O 4 ( 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 Co 3− x Fe x O 4 to the coexisted phases of Co 3− x Fe x O 4 and CoFe 2O 4, which is accompanied with the enhancement of the ferromagnetic (FM) response. In addition, the horizontal negative exchange bias (EB) effect was observed in the Fe 3+ doped samples. For Co 3− x Fe x O 4 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) Co 3O 4. While for Co 3− x Fe x O 4 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 Co 3− x Fe x O 4 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.