The Preparation,characterization And Coupling Of La_0.67Sr_0.33MnO₃,Sr₂FeMoO₆ And LaMnO₃

Recently,the study of perovskite has become a hotspots.Three kinds of La_0.67Sr_0.33MnO₃samples（A,B and C）were prepared by hight temperature solid state method in this paper.A:all steps were sintered in the air.B:the final step was sintered in oxygen atmosphere at 1300℃for 8 h and other steps were sintered in air.C:all steps were sintered in oxygen atmosphere.Its crystal structure,magnetic and electrical properties were determined.Three kinds of La_0.67Sr_0.33MnO₃ samples and Sr₂FeMoO₆ were used to form a two layer coupling system.Three kinds of La_0.67Sr_0.33MnO₃ sample and LaMnO₃ were used to form a three layer coupling system,such as A/LaMnO₃/A.The electrical and magnetic properties of the two-layer coupling system were measured and the electrical properties of the three-layer coupling system were measured.The crystal structures of perovskite La_0.67Sr_0.33MnO₃ series samples had been successfully synthesized all belong to trigonal system.The space groups of these samples was R-3c.The maximum Mn-O-Mn bond angle of sample B was 167.15°.Its double exchange were the strongest.The saturation magnetization and Curie temperature of B was the highest among three samples,resistivity of B was the lowest among three samples,which were consistent with the structural data.The critical parameters of A:β=0.588（4）,γ=1.113（5）,δ=3.196.The critical parameters of B:β=0.408（4）,γ=1.063（5）,δ=3.196.The critical parameters of B:β=0.456（4）,γ=1.065（4）,δ=2.947.Theβshows all three samples are in accordance with the mean field model and the sample B was the most deviated from the mean field model.Theγshows the three samples were magnetic long-range interaction,the interation with exchange distance decay as J（r）≈r^-4.578,J（r）≈r^-4.598 and J（r）≈r^-4.598respectively.The conduction mechanism of sample A:The electrical transport behavior under a zero field is mostly controlled by double magnon scattering in the temperature ranges from 280-345 K.The electrical transport behavior in a 1 T field is mostly controlled by electron-electron and electron-magnon scattering in the temperature ranges from 280-345 K.The electrical transport behavior under a zero field is mostly controlled by electron-electron and electron-magnon scattering in the temperature ranges from 345-395 K.The electrical transport behavior in a 1 T field is mostly controlled by double magnon scattering in the temperature ranges from 345-395 K.The conduction mechanism of semiconductor were the adiabatic small polaron hopping model.The conduction mechanism of sample B:The electrical transport behavior is mostly controlled by electron-magnon scattering in the temperature ranges from 280-360 K,the conduction mechanism of semiconductor were the nonadiabatic small polaron hopping model.The conduction mechanism of sample C:The electrical transport behavior is mostly controlled by electron-electron,electron-magnon and electron-phonon scattering in the temperature ranges from 280-360 K,the conduction mechanism of semiconductor were thermal activation model.The conduction mechanism of two layer coupling system and three layer coupling system were changed significantly by coupling.Due to coupling between monomers,the double exchange interaction were weakened and the corresponding Curie temperature and saturation magnetization decreases.