Investigation On The Doping Effect Of The Double Perovskite Oxides Sr₂MnMoO₆ And Sr₂FeMoO₆

As a research hotspot in the field of condensed state,the double perovskite oxides A₂BB'O₆ have many excellent properties due to the strong correlation between spin,charge,lattice and orbit,which make it potentially applied in magnetic storage and sensors.Therefore,the research on the regulation mechanism of the magnetoelectric properties of this oxides and the optimization of their performance have been attached great importance by researchers for a long time.In this paper,Sr₂MnMoO₆ and Sr₂FeMoO₆ were chosen as the research objects.The effects of electron doping and hole doping on the structure,surface morphology and magnetoelectric properties of Sr₂MnMoO₆ and Sr₂FeMoO₆were studied.Firstly,the series of samples of Bi³⁺doped Sr_2-x-x Bi_xMnMoO₆?x=0-0.25?were prepared by conventional solid-state reaction method,X-ray diffraction,Rietveld refinement,scanning electron microscope,energy-dispersive spectrometry and magnetic tests have been curried out to explore the electron doping effect on Sr₂MnMoO₆.According to the results of Rietveld refinement,the space group of all samples belong to I4/M,and there are no phase transitions with the increase of Bi³⁺doping level.The degree of Mn/Mo order???and the unit cell volume?V?of all these samples decreace with the enhance of Bi³⁺doping level.After a careful observation and analysis,the doped samples present bigger grains than that of Sr₂MnMoO₆ as the effumability of Bi₂O₃,which introduce a liquid sintering process.Magnetic tests indicate that all samples are antiferromagnetic,but the Mn²⁺-Mo⁵⁺electron pairs appear in the Bi³⁺doping samples,which produce weak ferromagnetic behavior in doped samples.Under the comprehensive regulation of the Mn/Mo anti-site defect?ASD?and the ferromagnetism produced by the Mn²⁺-Mo⁵⁺electron pairs,both the magnetization and the Neel Temperature T_N of the doped samples increase firstly and then decrease with the increase of the Bi³⁺doping amount of x.After that,gradually reduced the content of Strontium in Sr₂FeMoO₆ A sites to prepare the hole doping system Sr_2-xFeMoO₆.The effects of hole doping on the structure,magnetic properties and magnetic transport properties of Sr₂FeMoO₆ were investigated.The results indicate that all samples belong to the Fm3m space group.Under the effect of hole doping,the cell volume and Fe/Mo order of the series of samples gradually decrease with the increase in hole doping amount.The magnetic measurement showed that all the samples were all ferromagnetic,and the increase in the hole level reduced the saturation of magnetization M_S and Curie temperature T_C.The theoretical M_S were calculated by the modified formula which based on the FIM model,the calculated results can be well fitted with the M_S of the experimental value.At 300K,magnetoresistance values?MR?of the series of samples decreased with the enhance of hole doing content,the effect of the pinning effect on magnetic domain that caused by the anti-site defect can be responsible for the variation of the MR value of the hole doping system.