L. Shi

Structural, transport and magnetic properties of RuSr2Sm1.4Ce0.6Cu2O10−δ

yThe structural, transport and magnetic properties of RuSr2Sm1.4Ce0.6Cu2O10-delta have been studied. The increase of oxygen content results in a decrease of lattice parameters and an increase of superconducting transition temperature. For Raman spectra, the hardening of the 650 cm(-1) mode with decreasing temperature is due to the thermal contraction of lattice. Magnetic measurements exhibited a ferromagnetic transition around 150 K, indicating the coexistence of superconductivity and ferromagnetism in this compound

Superconducting properties of MgB2 wires and tapes with different metal sheaths

Abstract We have successfully fabricated mono- and multifilamentary MgB 2 wires and tapes with different sheathed metals such as Cu, Ta, NbZr and Fe by the powder-in-tube method. The phase compositions, microstructure features and superconducting properties are investigated by X-ray diffractometer, optical microscopy, SEM, standard four-probe technique and SQUID magnetometer. The results indicate that there is no reaction between the sheathed metals used here except Cu. For the Cu/Ta/MgB 2 wire, the irreversibility field achieves 6.6 T at 5 K and J c is higher than 10 5 A/cm 2 at 5 K in self-field. By using NbZr as a buffer layer, 18-filamentary Cu/MgB 2 tapes show a transport high J c of 8×10 4 A/cm 2 (10 K self-field). Remarkably, we prepared the Fe/MgB 2 wire with high transport J c of 5.6×10 4 A/cm 2 (15 K, 3 T) and 5.1×10 4 A/cm 2 (25 K, 2 T). The reasons for the improvement of J c in high fields were briefly discussed.

Energy dissipation in Bi2Sr2CaCu2O8+δ single crystal

Abstract The in-plane resistivity of Bi 2 Sr 2 CaCu 2 O 8+ δ single crystal in different magnetic fields was measured for magnetic field H parallel and perpendicular to the CuO 2 plane. The irreversibility line H irr ⊥ c ( T ) for H parallel to the CuO 2 plane locates in higher field and higher temperature region in the H – T phase diagram than H irr ∥ c ( T ) for H perpendicular to the CuO 2 plane. H irr ∥ c ( T ) is dominated by surface barrier pinning, while H irr ⊥ c ( T ) shows different temperature dependencies above and below 2 T, which may indicate different energy dissipation above and below the field. The field dependence of activation energy above 2 T in H ⊥ c configuration could be explained by vortex–antivortex expansion in CuO 2 plane.

Effect of Pb doping on the superconducting and magnetic resonance properties of Ru-1222

Abstract The resistivity, electron paramagnetic resonance (EPR) and microstructure of polycrystallines Ru 1− x Pb x Sr 2 Gd 1.4 Ce 0.6 Cu 2 O 10− δ ( x =0, 0.03, 0.2, 0.4, 0.5) have been studied systematically. Pb doping reduces the conductivity and suppresses the superconductivity, which may reflect the increase in hole localization due to disorder effects resulting from Pb doping. The temperature dependencies of magnetic resonance for samples Ru 1− x Pb x Sr 2 Gd 1.4 Ce 0.6 Cu 2 O 10− δ show that there are two absorption peaks. The first one around the magnetic field 3300 Oe corresponds to the electron paramagnetic resonance (EPR) of the Gd ions, and the second that appears below the ferromagnetic transition temperature is a ferromagnetic resonance (FMR) due to the ordered Ru ions.

Transport and magnetic resonance properties of Ru1−xSbxSr2Gd1.4Ce0.6Cu2O10−δ

Abstract The resistivity, electron paramagnetic resonance (EPR) and microstructure of polycrystallines Ru 1− x Sb x Sr 2 Gd 1.4 Ce 0.6 Cu 2 O 10− δ ( x =0, 0.01, 0.02, 0.05, 0.07) have been studied systematically. Sb doping reduces the conductivity of the system and the onset superconducting transition temperature decreases from 42 K for x =0 to 19 K for x =0.07. This may reflect the increase in hole localization due to a distortion of RuO 6 octahedra. The temperature dependencies of magnetic resonance for samples Ru 1− x Sb x Sr 2 Gd 1.4 Ce 0.6 Cu 2 O 10− δ show that there are two absorption peaks. The first one around the magnetic field 3300 Oe corresponds to the EPR of the Gd ions, and the second that appears below the ferromagnetic transition temperature is a ferromagnetic resonance due to the ordered Ru ions.

Structural modifications and phonon softening in Bi2Sr2Ca1−xRxCu2O8+δ (R = Pr and Gd) single crystals

The phonon Raman spectra of Bi2Sr2Ca1-xRxCu2O8+delta (R = Pr and Gd) single crystals are systematically investigated. The experimental results show that the O(2)(Sr)A(1g) mode softens with Pr and Gd doping, while the O(1)(Cu) B-1g mode softens with Pr doping but hardens with Gd doping. The changes of average ionic radius on the Ca site in Bi-based cuprates can account well for the Raman frequency shifts of the O(I)(Cu) mode, but have little influence on the O(2)(Sr) mode. The frequency softening of the O(2)(Sr) mode in Pr- and Gd-doped Bi2212 crystals mainly results from contraction of the BiO bilayers with doping content. The correlation between the O(2)(Sr) mode frequency and the c-axis parameter as well as the incommensurate modulation wavelength is discussed.

Effects of Ba doping on Tc and vibration features of (Pb, Cd)-1212 cuprates

Abstract Samples of nominal composition (Pb 0.5 Cd 0.5 ) (Sr 2− x Ba x ) (Ca 0.5 Y 0.5 )Cu 2 O y (0⩽ x ⩽0.5) synthesised at 920°C in air are investigated. XRD shows the samples to exhibit the tetragonal 1212-phase. The lattice parameters, the width of the Raman peak for the apical-0(2) vibration mode and the infrared absorption peak for the 0(3) vibration mode, all increase with increasing Ba doping level. In the doping range (0.0⩽ x ⩽0.5), there is a transition from insulator to superconductor. The Raman shift and the wavenumber of the infrared absorption for the phonon peaks appear to change regularly.

Irreversibility line in the superconductor RuSr2Gd1.4Ce0.6Cu2O10−δ

Abstract The resistive transition of the superconductor RuSr2Gd1.4Ce0.6Cu2O10−δ is measured under magnetic fields from 0 to 10 T. The results show that the irreversibility line determined from the different reduced resistivity criterion can be fitted well by the expression: Hi=α(1−T/Tc)γ. The activation energy (U) is obtained from the low dissipation parts of the ρ(T) curves using the Arrhenius activation law ρ(T,H)=ρ0(H)exp{−U(H)[1−T/Tc]/kBT}. The U value obtained is smaller than that of other high temperature cuprate superconductors, which may be due to the coexistence of superconductivity and ferromagnetism in RuSr2Gd1.4Ce0.6Cu2O10−δ. It is also found that the activation energy can be fitted by U=157H−0.59.

Anomalies in thermoelectric power at 200 K in the calcium-doped NdCeCuO system

Samples of are characterized by thermoelectric power and variable-temperature x-ray diffraction. For the superconducting sample , S is positive in the whole measuring temperature range and weakly dependent on temperature; for the Ca-doped samples, , S shows a negative and strong dependence on temperature at low temperature for large x. It is striking that Ca doping leads to a sharp peak at about 200 K for either the superconducting samples or the nonsuperconducting samples . The strength of the peak increases with increasing x. Low-temperature x-ray diffraction shows that the lattice parameters decrease with decreasing temperature and an anomaly is observed at the corresponding temperature.

Formation of a new series of 1222 layered cuprates (Cd,M)Sr2(Gd,Ce)2Cu2Oy (M=Ce, Sn, Mo and V)

Abstract We have synthesized new layered cuprates (Cd 0.5 M 0.5 )Sr 2 (Gd 2− x Ce x )Cu 2 O y , with M=Ce, Sn, Mo and V. The structure of the compounds is directly related to that of (Pb,Cu)-1222, with (Cd,M) occupying the (Pb,Cu) site. Resistivity measurements show that all the samples are narrow-gap semiconductors.