The Behavior Of Electron-spin In Bi-based Oxides And Si-based Alloys

In this paper, the behavior of electron-spin in Bi-based oxides and Si-based alloys was studied in detail. Bi2Sr2CaCu2Oy(Bi-2212) was chosen as a parent compound, and the effect of La substitution for Bi in Bi-2212and Mn for Cu on the structure and physical properties of Bi1.4La0.6Sr2CaCu2Oy was investigated, respectively. The large grain growth method and the influence of grain integrity on physical properties of Pr2CuSi3ternary Si-based alloys were investigated. The details are as followed:The Bi2-xLaxSr2CaCu2Oy(0≤x≤4.5%) powder was prepared by sol-gel method, structural characteristics were measured by X-ray diffraction patterns (XRD) and infrared absorption (IR) spectroscopy. The temperature dependence of resistance (R-T) was measured by the standard four-probe technique, and the variation of structure and physical properties by the equivalent substitution of La+for Bi+ions were studied. Results indicated that a and b lattice parameters increased gradually and c decreased monotonously with the increase of La doping level. The increase of a and b induced by the flatness of CuO2planes was confirmed by the result of IR spectrum and XRD, which accompanied the increase of O-Cu-O angle. R-T results implied that the decrease of TcZero and the increase of△TC were caused by the change of microstructure of CuO2planes. On the analysis of Tc,onset, it was found that the increase of Tc,onset in Bi-2212system could be induced by magnetism which was brought by the spin of itinerant electrons.The Mn doped Bi1.4La0.6Sr2CaCu2-xMnxOy (0≤x≤4.5%) powder was prepared by sol-gel method, structural characteristics were measured by XRD, IR and Raman scattering spectroscopy, and the physical properties were measured by the standard four-probe technique and vibrating sample magnetometer (VSM). Results indicated that Mn atoms were successfully entered into Bi1.4La0.6Sr2CaCu2Oy compounds which were ensured by the Pawley refinement. With the increase of Mn doping level, lattice parameter a initially increased and then decreased, however, both b and c lattice parameters decreased monotonously. The deduction of CuO2planes canting and Mn aliovalence which was confirmed by IR and Raman spectrum was obtained from variation of lattice parameters. By the analysis of resistivity curves, it was found that the samples exhibited insulating character which had very large resistivity, discussed by Mott model. In the condition of preserving Bi-2212structure, Bi1.4Lao.6Sr2CaCu2-xMnxOy compound has optimal resistivity and magnetism at x=2%, which could be a new insulating material in Josephson junction in future.Pr2CuSi3ternary Si-based alloy were prepared by arc-melting in arc furnace, structural characteristic was measured by XRD and metalloscope, and composition was identified by Energy dispersive X-Ray Spectrometer (EDX), and the physical properties were measured by the standard four-probe technique, Van der Pauw Method, superconducting quantum interference device (SQUID) and physical property measurement system (PPMS). It was found that800℃was the best annealing temperature and the effect of annealing on grain growth was limited. In order to accelerate grain growth, compression deformation was introduced. The statistics of average grain size at different pressure with the same annealing time indicated that optimal pressure can accelerate grain growth immensely. Especially, a huge grain with approximate size of0.6mm×0.6mm, was observed in the sample that was compressed at36.7MPa and annealed for240hours. Such giant grain could be isolate to substitute single crystal. By the analysis of resistivity and hall coefficient, it was found that the increase of grain size can improve spin freezing temperature, which was confirmed by ac magnetic susceptibility. Ac susceptibility results indicated that the spin freezing temperature was improved more than4K in the huge size grain, which was found in the sample that was compressed at36.7MPa and annealed for240hours.