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The transition-metal dichalcogenides provided a good platform for the investigation of superconductivity and charge-density-wave (CDW) order. A series of high quality 6R-TaS2-xSex (0≤x≤1.6) single crystals were fabricated by the chemical-vapor-transport method and systematically investigated. The CDW becomes more stable with more S being replaced by Se, which causes expansion of the lattice, and produces a negative chemical pressure in the system. The x dependence of the onset of superconductivity (Tconset) shows a dome-like shape with a maximum of Tconset=2.7K at x=0.8. The magnetic susceptibility (4πχ) of x=0.8 under the hydrostatic pressure P=1.0 GPa was also measured, which showed a small increase of Tc and superconducting volume fraction. A pronounced peak effect was observed in the isothermal hysteresis with magnetic field (H) parallel to c-axis, which may arise from the quenching inhomogeneity and/or the stacking disorder. Finally, the evolution of the electronic states tuned by Se-doping was summarized in the phase diagram. [ABSTRACT FROM AUTHOR]

The metal-oxide-semiconductor field-effect transistor (MOSFET) device containing silicon nanocrystals (nc-Si) is fabricated by an ion-beam technique. The parasitic effect in the subthreshold region is only observed by the application of high erasing pulses. By using the second derivative method, the formation of the parasitic transistor is confirmed. The parasitic transistor is only activated upon the trapping of holes into the nc-Si at the edge channel. In addition, electron or hole trapping in the nc-Si depend on the voltage polarity and magnitude, which lead to positive or negative shifts in the threshold voltage. This demonstrates the feasibility of memory applications in MOSFET device. [ABSTRACT FROM AUTHOR]

We investigate the exchange bias phenomenon in the layered cobaltite Sr1.5Pr0.5CoO4 by using magnetometry. The exchange bias is strongly dependent on the cooling magnetic field as well as the measuring field. These results suggest that the exchange coupling at the interfaces between the ferromagnetic (FM) regions and the spin-glass (SG) regions may induce an exchange anisotropy. The observed exchange bias effect is suggested to originate from the pinning to FM moments by frozen spins in the SG regions along the cooling field direction. Our results also expand the concept of the magnetically tunable exchange bias, which can contribute to the potential applications for spintronic devices. [ABSTRACT FROM AUTHOR]

We investigate the exchange bias phenomenon in the layered cobaltite Sr1.5Pr0.5CoO4 by using magnetometry. The exchange bias is strongly dependent on the cooling magnetic field as well as the measuring field. These results suggest that the exchange coupling at the interfaces between the ferromagnetic (FM) regions and the spin-glass (SG) regions may induce an exchange anisotropy. The observed exchange bias effect is suggested to originate from the pinning to FM moments by frozen spins in the SG regions along the cooling field direction. Our results also expand the concept of the magnetically tunable exchange bias, which can contribute to the potential applications for spintronic devices. [ABSTRACT FROM AUTHOR]

We present the results of systematic study of structure, magnetic properties, and electrical transport in layered cobaltites Sr2-xPrxCoO4 (0.5≤x≤1.5). The variations of Jahn–Teller distortion of CoO6 octahedron reflected by two different Co–O bond lengths indicate that all the samples are mostly accommodated in the t2g orbital states. For x<1 samples, with increasing Pr-doping level, the tolerance factor decreases and the distortion of CoO6 octahedron enhances, which result in the increased bending of Co–O–Co bond, the narrowing of the bandwidth, and the decrease of the mobility of eg electrons caused by the substitution of smaller Pr3+ ions for a larger Sr2+ ion. For x>1 samples, the contribution of carrier density should be considered besides the tolerance factor. [ABSTRACT FROM AUTHOR]

We present the results of systematic study of structure, magnetic properties, and electrical transport in layered cobaltites Sr2-xPrxCoO4 (0.5≤x≤1.5). The variations of Jahn–Teller distortion of CoO6 octahedron reflected by two different Co–O bond lengths indicate that all the samples are mostly accommodated in the t2g orbital states. For x<1 samples, with increasing Pr-doping level, the tolerance factor decreases and the distortion of CoO6 octahedron enhances, which result in the increased bending of Co–O–Co bond, the narrowing of the bandwidth, and the decrease of the mobility of eg electrons caused by the substitution of smaller Pr3+ ions for a larger Sr2+ ion. For x>1 samples, the contribution of carrier density should be considered besides the tolerance factor. [ABSTRACT FROM AUTHOR]

We have systematically investigated the influence of the Ag doping on magnetization M(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) in the layered cobaltites Bi2Ba3-xAgxCo2Oy (0≤x≤2) samples. For Ag-doped sample, the magnetic susceptibility indicates the ground state is dominated by the low-spin states of the combination of Co3+ and Co4+. The metal-insulator transition existing in Ag-free sample is suppressed and replaced by metallic behavior due to Ag doping. Moreover, S is remarkably large and temperature independent with metallic ρ(T) at high temperatures, which is suggested to be the evidence of a narrow a1g band. A steep upturn of ρ is observed at low temperature while no corresponding change appears in the S(T) curve. Such an abnormal behavior is attributed to Anderson localization in a narrow band. Additionally, the Ag doping not only introduces holes into the conducting CoO2 layers but also enhances the disorder which decreases the upper mobility edge EC. As to κ(T), it plays an important role for the contribution of mobile electronic carrier component κe besides the contribution of phononic component κph. The behavior of κe is ascribed to the effect of the competition between magnetic interaction and the disorder. The variation of κph is analyzed according to the combined effect due to the impurity and disorder because of Ag doping, which is favorable to the scattering of phonon leading to the decrease of κph, and the decreased scattering of interface between the CoO2 and the Bi–Ba–O blocks due to Ag doping, which contributes to the increase of κph. [ABSTRACT FROM AUTHOR]

We have systematically investigated the influence of the Ag doping on magnetization M(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) in the layered cobaltites Bi2Ba3-xAgxCo2Oy (0≤x≤2) samples. For Ag-doped sample, the magnetic susceptibility indicates the ground state is dominated by the low-spin states of the combination of Co3+ and Co4+. The metal-insulator transition existing in Ag-free sample is suppressed and replaced by metallic behavior due to Ag doping. Moreover, S is remarkably large and temperature independent with metallic ρ(T) at high temperatures, which is suggested to be the evidence of a narrow a1g band. A steep upturn of ρ is observed at low temperature while no corresponding change appears in the S(T) curve. Such an abnormal behavior is attributed to Anderson localization in a narrow band. Additionally, the Ag doping not only introduces holes into the conducting CoO2 layers but also enhances the disorder which decreases the upper mobility edge EC. As to κ(T), it plays an important role for the contribution of mobile electronic carrier component κe besides the contribution of phononic component κph. The behavior of κe is ascribed to the effect of the competition between magnetic interaction and the disorder. The variation of κph is analyzed according to the combined effect due to the impurity and disorder because of Ag doping, which is favorable to the scattering of phonon leading to the decrease of κph, and the decreased scattering of interface between the CoO2 and the Bi–Ba–O blocks due to Ag doping, which contributes to the increase of κph. [ABSTRACT FROM AUTHOR]

We present the results of a systematic study of the transport mechanism and magnetothermoelectric power (MTEP) of electron-doped manganites La0.85Te0.15Mn1-xCuxO3 (0<=x<=0.20). Two peaks are observed in thermoelectric power S(T) curves for x<0.10 samples. For x>0.10 samples, the very large S value with over 100 μV/K at low temperatures appears, which is attributed to the destruction of ferromagnetic (FM) order and the strong carrier localization at low temperatures due to Cu doping. In addition, a sign variation of S(T) for Cu-doped samples is also observed, which may originate from the narrowing of the concomitant σ(eg↑-2p) band. Particularly, an anomalous behavior of S(T) is observed in x=0.10 sample, which is suggested to be related to the contribution of spin polarization and phonon drag. Based on the results of resistivity ρ(T) and S(T), the transport mechanism in the high-temperature paramagnetic region for all the samples and low-temperature FM insulating region below TC for the samples with x<=0.10 can be described by the variable-range-hopping model. However, in the intermediate-temperature FM metallic region below TC, ρ(T) and S(T) of the samples with x<=0.10 are well fitted by the formula ρ=ρ0+ρ2.5T2.5 and S=S0+S3/2T3/2+S4T4, respectively, implying the importance of electron-magnon scattering. As to the MTEP, only a negative MTEP peak close to TC is observed in the whole measured temperature range for the samples with x>0.10, which is suggested to originate from the spin alignment induced by applied magnetic fields. However, for x<=0.10 samples, an additional positive MTEP peak is induced by Cu doping below TC besides a large negative MTEP peak in the vicinity of TC, which is ascribed to the enhancement of electron-magnon interaction caused by the Cu doping and the decrease of magnetic entropy around TC, respectively. [ABSTRACT FROM AUTHOR]

The effects of V doping on field-cooled magnetization MFC(T), zero-field-cooled magnetization MZFC(T), resistivity ρ, thermoelectric power S, and thermal conductivity κ in manganites CaMn1-xVxO3 (0.02<=x<=0.08) have been investigated systematically. As the V doping level exceeds 0.02, an anomalous “diamagnetism” has been observed. It is suggested that the force generated by the orbit rotation of eg electron in Mn3+O6 octahedron makes the spin tilt, as a result, the vector sum of individual spins may be along or opposite to the direction of the applied magnetic field, and macroscopically, the average magnetization exhibits positive or negative values. In addition, the transport mechanism in the high and low temperature ranges is dominated by the small polaron conduction and the variable-range-hopping conduction, respectively, according to the fitting analysis of the temperature dependence of Seebeck coefficient S(T) and resistivity ρ(T). Both S and κ peaks appearing at low temperature is gradually suppressed by V doping. Additionally, obvious magnetothermoelectric power and magnetothermal conductivity are observed in the temperature region which an anomalous diamagnetism appears. The results are discussed based on spin-orbital coupling and spin-phonon coupling induced due to V doping, respectively. Moreover, the large thermoelectric figure of merit Z=S2/ρκ for the slightly V-doped sample suggests that the V-doped manganite may be a good candidate for thermoelectric materials. [ABSTRACT FROM AUTHOR]

The exchange bias phenomenon in the layered cobaltite [Sr.sub.1.5][Pr.sub.0.5]Co[O.sub.4] is examined by using magnetometry. The exchange bias effect has originated from the pinning to ferromagnetic (FM) moments by frozen spins in the spin-glass (SG) regions along the cooling field direction.

The influence of the V doping on [M.sub.FC](T), [M.sub.ZGC](T), p(T), S(T) and l(T) of Ca[Mn.sub.(1-x)][V.sub.x}O3 (0.02 less than or equal to x less than or equal to 0.08) samples is systematically investigated. Results reveal that as x > 0.02, an anomalous diamagnetism is observed.

We have performed temperature-dependent synchrotron radiation x-ray absorption fine structure (XAFS) spectra of layered transition metal dichalcogenide 1T-TaS2-xSex to elucidate the local electronic and atomic structure especially associated with the occurrence of superconductivity for the first time. We observed a corresponding temperature-dependent phase transition from nearly commensurate to commensurate charge density wave, as well as a characteristic of p-d hybridization between Ta 5d and Se 4p states, which is favorable to boost superconductivity, determined by x-ray absorption near edge structure (XANES) spectra at the Ta L3-edge and Se K-edge, respectively. And also, the periodic lattice distortion accompanied by the occurrence of charge density wave is clearly demonstrated by extended XAFS (EXAFS) spectra at the Ta L3-edge of the pristine sample 1T-TaS2, which is clearly suppressed in the Se-doping sample 1T-TaSSe with a maximum transition temperature. The present results reveal that the p-d hybridization and the loss of long-range coherence of the CDW state play an important role in manipulating the superconductivity, shedding new light on the physics mechanism of the interplay between superconductivity, charge order, and electron correlation. [ABSTRACT FROM AUTHOR]