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The thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics, reduced in various conditions, were investigated in the temperature range from 323K to 1073K. Both the electrical resistivity and the absolute Seebeck coefficient decreased with the deepening degree of oxygen-reduction. However, the decrease of the electrical resistivity had a major influence on the thermoelectric power factor. Therefore, the more heavily reduced sample can gain the higher value of thermoelectric power factor. It has been observed that the thermal conductivity increased with the deepening degree of oxygen-reduction, which indicates that the scattering of the oxygen vacancies produced by reduction does not play a dominant role in the thermal conduction. In spite of the increase of the thermal conductivity, the oxygen-reduction still promoted the thermoelectric figure of merit via the increase of the thermoelectric power factor. And the most heavily reduced Sr0.61Ba0.39Nb2O6 ceramic has the highest thermoelectric figure of merit (~0.18 at 1073 K) among all the samples.

The magnetic and electrical properties of the La0.67Ca0.25Sr0.08MnO3/xAg composite system are systematically investigated as a function of Ag-added content. With increasing the Ag dopant amount, the magnetization decreases a little while Curie temperature (TC) is almost independent of Ag content around 312 K. The resistivity reduces rapidly with Ag addition ( x < 0.25 ) due to the decomposed metal Ag, and then it increases slightly which is probably induced by the less Ag content related to the volatilization of Ag during calcinations. At low temperature, the ρ – T curves fit well by the expression of ρ =ρ0 +ρ2T2 +ρ4.5T4.5 while all data for the above TC can be fitted by using the adiabatic small-polaron-hopping model ρ=ρ0T exp (E/kBT ). The enhancement of MR effect ( 41% ) at room temperature is mainly related to the coexistence of intrinsic MR properties and the spin dependent scattering of conduction electrons at the interfaces. These results indicate that combining the doping effect with the composite method is an effective selection in enhancement of MR at room temperature, which is very meaningful for the application research.

The magnetic and electrical properties of La0.67Sr0.33MnO3 ( LSMO ) are influenced very much by the Nb dopant. However, this doping effect is restricted by the limited Nb solution into LSMO due to the low calcined temperature. As a result, a second phase LaNbO4 appears in our samples. Enhancements of the low-field magnetoresistance (LFMR) were observed both at 77 K and room temperature in the manganite system prepared by doping Nb2O5 into LSMO powders. The doping amount x of Nb ions ranges from 0-10 % molar ratio. The MR ratios at 77 K with H = 1 T and H = 0.1 T are 33.8 % and 24 % for the x = 0.07 doped sample, respectively. A MR effect up to 9 % was also found for the sample with x = 0.05 at room temperature, which is 2.2 times as large as that for LSMO (4.1%). The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the LFMR while the high field magnetoresistance (HFMR) originates from the spin dependent transport related to noncollinear spin structure at the interfaces.

Abstract: Multilayered FeSi/Si amorphous films with fixed FeSi layer thickness and different Si layer thicknesses have been studied by conversion electron Mssbauer spectroscopy at room temperature. The results showed that with decreasing the Si layer thickness, the hyperfine field of samples increased and the thickness of interface dead layers arisen from the atomic interdiffusion effect decreased. These are due to the coupling effect between the magnetic layers.

CoNb/Cu multilayers with amorphous CoNb magnetic layers were prepared by rf-sputtering method and then annealed at various temperatures in a high vacuum. A maximum magnetoresistance ratio of 2.83% at room temperature was obtained under a relatively low saturation field of about 200 Oe for the optimum annealing temperature of 400° C. The structural, magnetic and transport properties were strongly influenced by the annealing temperature, and the transport properties were explained on the basis of granular multilayered structures. The magnetoresistance ratio also depends on the thickness of CoNb and Cu layers.