Magnetic And Electrical Properties Of Doped Perovskite Oxides La_2-xSr_xCo/NiMnO₆?0<x?0.5?

La2NiMnO6 and La2CoMnO6,as two typical double perovskite oxides,have outstanding physical properties,such as high Curie temperature,obvious magnetocapacitance effect and giant magnetoresistance effect.They exist potential application values in magnetic memory materials and spin-electron device.The physical properties of materials can be controlled effectively by ions doping and substituting.Ions doping is an significant method for the exploration of new-type multi-functional materials with excellent properties.In this dissertation,the effects on the physical properties of these materials were analyzed with Sr2+ doped in La site.XRD was used to characterize the crystal structure and PPMS was used to characterize magnetic and electrical properties.The obtained main results are shown as followed:1.Magnetic and electrical transport properties of La2-xSrxNiMnO6(0<x?0.5).La2-xSrxNiMnO6(x = 0.1,0.2,0.3,0.4,0.5)polycrystalline samples were synthesized by the solid-state reaction and were studied the effects on the crystal structure and magnetic,electrical properties with Sr-doping.The crystal structure has been confirmed to be a single phase with rhombohedral structure(space group R3m)at room temperature,the crystal structure changed a little with Sr-doping.All doped samples show ferromagnetic behavior in low temperature.The ferromagnetism weakened with the increasing Sr2+ content,however,Curie temperature TC are almost unchanged in doped samples.Resistivity measurement results reveal that all samples have semiconductor behavior,and the conduction mechanism can be well fitted by the variable-range hopping model.La2-xSrxNiMnO6(x = 0.1,0.2,0.3,0.4,0.5)samples exhibit the negative magnetoresistance effect.At 150 K and 200 K,small amount of Sr-substitution(x?0.2)can enhance the magnetoresistance effect.The negative magnetoresistance effect of x =0.2 can be up to 9%measured at 150 K under 7 T.The results provide the experimental foundation for researching A-site substitution of double perovskite materials.2.Magnetic and electrical transport properties of La2-xSrxCoMnO6(0<x<0.5).La2-xSrxCoMnO6(x = 0.05,0.1,0.15,0.2,0.3,0.5)polycrystalline samples were synthesized by the solid-state reaction.The effects on the crystal structure and magnetic,electrical properties with Sr-doping was studied.Samples have been refined to rhombohedra structures at room temperature.The exchange bias effect is enhanced by Sr2+ substitution.It originates from the spin coupling at the ferromagnetic and antiferromagnetic interfaces.All samples have semiconductor behavior,the resistivity was decreased by increasing tempurature.La2-xSrxCoMnO6(x = 0.05,0.1,0.15,0.2,0.3,0.5)samples also exhibit the negative magnetoresistance effect.At 150 K and 200 K,small amount of Sr-substitution can enhance the magnetoresistance effect.The negative magnetoresistance effect of x = 0.2 can be up to 47%measured at 150 K under 7 T.These results may provide the experimental evidence for enhancing the exchange bias effect and the magnetoresistance effect of double perovskite oxide.