Effects of Bi doping on structural and magnetic properties of double perovskite oxides Sr2FeMoO6

Abstract A new series of double perovskite compounds Sr 2 −  δ Bi x FeMoO 6 have been synthesized by solid-state reaction. δ refers to the nominal doping content of Bi ( δ = 0 , 0.1, 0.2, 0.3, 0.4, 0.5), while the Bi content obtained by the Rietveld refinement is x = 0 , 0.01, 0.05, 0.08, 0.10 and 0.12. Their crystal structure and magnetic properties are investigated. Rietveld analysis of the room temperature XRD data shows all the samples crystallize in the cubic crystal structure with the space group Fm 3 ‾ m and have no phase transition. SEM images show that substituted samples present a denser microstructure and bigger grains than Sr 2 FeMoO 6 , which is caused by a liquid sintering process due to the effumability of Bi. The unit cell volume increases with augment of Bi 3+ concentration despite the smaller ionic radius Bi 3+ compared with the Sr 2+ , which is attributed to the electronic effect. The degree of Fe/Mo order ( η ) increases first and then decreases to almost disappearance with augment of Bi doping, which is the result of contribution from electronic effect. Calculated saturation magnetization M s ( 3 ) according to our phase separation likeness model matches well with the experimental ones. The observed variations of magnetoresistance (MR) are consistent with the Fe/Mo order ( η ) due to the internal connection with anti-site defect (ASD).