Low-spin Co3+ make great contributions to the magnetism of BiFeO3

Abstract

Various spin states of Co3+ were tested in Co-doped BiFeO3 (BFO) through first-principle method, aimed to reveal the role of spin state transition of Co3+ in developing ferrimagnetism. It is found that low-spin (LS) Co3+ contributed much more to resultant magnetic moment than high-spin (HS) Co3+ (~ 3.914 µB). To explore the electronic origins of the enhanced magnetism, a more detailed analysis is carried out including electronic configuration of HS and LS Co3+ as well as Co–O hybridization. It is demonstrated that the LS Co3+ which is nonmagnetic could destroy the cycloid–dal spin structure of BFO. Moreover, LS Co3+ has vacant 3d orbitals so that the p–d covalency is enhanced and the local ferrimagnetism is improved. The structural origin of the Co3+ spin-state transition is ascribed to the distortion of CoO6 octahedra. To explore the influence of Co doping experimentally, the 8% Co-doped and un-doped BFO powders were prepared. The Hysteresis loops indicated that the substitution of Co led to a slight increase of magnetization, i.e. HS Co3+ made limited contribution to the magnetism of BFO.