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Co2MnSi thin films are made by magnetron sputtering onto MgO (001) substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550°C and subsequently annealed at 550°C (sample I) exhibits a pseudo-epitaxial growth with partially ordered L21 phase. Sample I shows a four-fold magnetic anisotropy, in addition to a relatively weak uniaxial anisotropy. The Gilbert damping factor of sample I is smaller than 0.001, much smaller than reported ones. The possible reasons responsible for the small Gilbert damping factor are discussed, including weak spin-orbit coupling, small density of states at Fermi level, and so on. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of Sr0.61Ba0.39Nb2O6−δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ∼0.19 at 1073 K in the heaviest oxygen reduced sample. [ABSTRACT FROM AUTHOR]

The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3 (110) interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface, the interface Ti 3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of BaTiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2py state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface MgO layer leads to a magnetic moment of about 0.25μB per O atom at the interface. These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces. [ABSTRACT FROM AUTHOR]

The effects of Ag addition in Ti-doped La0.67Ba0.33MnO3 (LBT) (abbreviated as LBT/Agx, where x is the nominal molar ratio of Ag) on the electric and magnetoresistance (MR) properties have been studied systematically. The results show that the resistivity of the samples decreases dramatically with increasing Ag addition and reaches its minimum for x = 0.27. The room-temperature MR ratio of LBT/Agx increases with increasing x and reaches its maximum at x = 0.27. The MR ratio at 280 K for the x = 0.27 sample at H = 10 kOe is as large as 41%, which is about 3.4 times larger than that for LBT. The Ag addition makes the LBT crystallites more perfect and uniform, and suppresses the magnetic scattering at the grain boundaries. The Ag conduction channels penetrating into the insulating regions can also lower the resistivity. The near room-temperature TC and low resistivity of the Ag-added LBT are responsible for the large intrinsic room-temperature MR. [ABSTRACT FROM AUTHOR]

Abstract: A novel approach was developed to calculate temperature-dependent Seebeck coefficient of heavily doped systems. The electronic density of states (DOS) and Fermi energy were determined and then, using these two parameters, the Seebeck coefficient was calculated by using Boltzmann transport theory. This approach is applied to heavily La-doped SrTiO3. The calculated Seebeck coefficient agrees well with the experimental data. By analyzing the results, it was shown that Seebeck coefficient is greatly affected by the asymmetry of DOS with respect to Fermi energy. [Copyright &y& Elsevier]

Abstract: TiO2:Co thin films of high Co concentration were investigated by the high resolution transmission electron microscopy, physical property measurement system and energy dispersive X-ray. The as-deposited films are amorphous magnetic semiconductors and we did not find any Co metal particles in them. The electronic transport process in the low-temperature range below 80K could be described by the spin-dependent variable-range-hopping process. However, after the samples were annealed at 300°C, large amounts of Co metal particles were observed to connect each other and the films show a metallic behavior. The origin of ferromagnetism of the thin films is also discussed. [Copyright &y& Elsevier]

Abstract: Structural, magnetic, electrical, and magnetotransport properties have been carried out on the Ag-added La0.67Ba0.33MnO3/(TiO2)0.035 (LBT) (abbreviated by LBT/Ag x ,) composites. Ag addition has little influence on the magnetization or Curie temperature (T C), but decreases the resistivity (ρ) and sharps the ρ peak evidently. The ρ in the ferromagnetic (FM) metallic regime is proportional to T 2, reflecting that the conductive mechanism mainly arises from the electron–electron scattering. In the paramagnetic (PM) insulating region, the ρ data fit well to the self-trapped small polaron hopping model. The ρ–T curves for x =0.27 and 0.30 samples fit well with the phenomenological percolation approach, which is based on the phases segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. These excellent agreements highlight the dominant intrinsic behavior of LBT. In addition, from the magnetotransport measurements, a large magnetoresistance (MR) ratio up to 41% was obtained at 280K, and 10kOe for x =0.27 sample. The good fits between the field dependence of MR and Brillouin function indicate that the MR behavior in the Ag-added LBT is induced by the spin-dependent hopping of the electrons among the spin clusters, and which is related to the increase and growth of the FM spin clusters. [Copyright &y& Elsevier]

Abstract: We have prepared a series of polycrystalline manganites with the nominal compositions, La0.67Ba0.33Mn0.88Cr0.12O3/Ag x (LBMCO/Ag x ) (x is the mole fraction) with , 0.05, 0.1, 0.15, 0.2, 0.23, 0.27, 0.3, 0.35. The X-ray diffraction patterns show that the samples with are two-phase composites. The Ag addition in LBMCO improves the properties of grain surfaces/boundaries and reduces the resistivity of the composites. For sample, a minimum resistivity is obtained and a maximum room temperature magnetoresistance up to −54.5% was observed at 288K, 1T field. The room temperature T C and the reduced resistivity are responsible for the enhancement of room temperature MR. [Copyright &y& Elsevier]

Abstract: The electrical and magnetoresistant properties of La0.67(Ca0.65Ba0.35)0.33MnO3/Ag x (abbreviated by LCBMO/Ag x ) have been studied. The results show that Ag addition causes a decrease of resistivity dramatically and especially induces a large enhancement of room temperature magnetoresistance (MR). The room temperature MR ratio for x=0.27 sample in 10kOe magnetic field is 41%, almost 20 times larger than that for x=0 sample. This enhancement is related to that the Curie temperature (T c) of the sample is near room temperature, as well as the significant reduction of resistivity. The good fits of experimental results for x=0.27 sample to Brillouin function indicate that the MR behavior in the Ag added LCBMO is induced by the spin-dependent hopping of the electrons between the spin clusters, which is an intrinsic property of the CMR materials. [Copyright &y& Elsevier]

Enhancements of the low-field (LFMR) and high-field magnetoresistance (HFMR) were observed in the manganite system prepared by doping Nb2O5 into La0.67Sr0.33MnO3 powders. The maximum MR ratios at 77 K with H=1 T and 1 kOe are 30% and 20% for the 0.07 molar ratio doped sample, which are 1.7 times and 1.6 times as large as that for LSMO, respectively. An MR effect up to 6.5% was also found for the sample with x=0.03 at room temperature (RT). The spin-dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the LFMR while the HFMR originates from a noncollinear spin structure in the surface layer. With increasing x, the Curie temperature (TC) decreases monotonically from 364 to 154 K while the temperature TP related to the peak resistivity decreases firstly to a minimum of 204 K (x=0.06) and then rises up to 240 K (x=0.1). There is a maximum resistivity ρ for the sample with x=0.06, which is higher than that for LSMO by five orders of magnitude. It is due to the enhancement of spin-dependent and independent scattering and tunneling effects on the interfaces of grain boundaries and inside the grains. [Copyright &y& Elsevier]

La0.67Ca0.33MnO3 (LCMO) fine powder was prepared by a sol–gel procedure. The effects of Ti addition in LCMO on the magnetic, transport and magnetoresistive (MR) properties have been studied systematically. With increasing Ti addition, the magnetization and Curie temperature for the samples decrease monotonously, and the resistivity increases dramatically. The MR effect increases first and then decreases after a maximum MR ratio is reached. When the amount of Ti addition is 5.5% (molar ratio), a maximum MR ratio as large as 500% in 10 kOe at 120 K was obtained, which is 25 times larger than that obtained by the undoped LCMO. The effect of Ti addition is to introduce local magnetic inhomogeneity and inducing spin clusters in the material. Fitting the experimental results to the Brillouin function proposed by Wagner et al. indicates that a possible explanation for the MR behaviour in the Ti-doped LCMO is the formation of spin clusters. [Copyright &y& Elsevier]

The electrical transport of DNA is closely related to the density of itinerant pi electrons because of the strong electron-lattice interaction. The resistivities of two typical DNA molecules [poly(dG)-poly(dC) and lambda-DNA] with varied densities of itinerant pi electrons are calculated. It is found that the dependence of the resistivity on the density of itinerant pi electrons is symmetrical about the half-filling state of itinerant pi electrons in poly(dG)-poly(dC). At the half-filling state, the Peierls phase transition takes place and poly(dG)-poly(dC) has a large resistivity. When the density of itinerant pi electrons departs far from the half-filling state, the resistivity of poly(dG)-poly(dC) becomes small. For lambda-DNA, there is no Peierls phase transition due to the aperiodicity of its base pair arrangement. The resistivity of poly(dG)-poly(dC) decreases with increasing length of the molecular chain, but the resistivity of lambda-DNA increases with increasing length. The conducting mechanisms for poly(dG)-poly(dC) and a few lambda-DNA molecules with varied densities of itinerant pi electrons are analyzed.