共查询到20条相似文献,搜索用时 609 毫秒
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Thomas W. Krause R. K. Nkum W. R. Datars 《Physica C: Superconductivity and its Applications》1993,210(3-4):333-342
Measurements of the resistivity and current dependent resistivity for small current densities ranging from 0.03 A/cm2 to 3.0 A/cm2 were performed with two Sn-doped and two Sb-doped polycrystalline Bi1.7Pb0.3Sr2Ca2Cu3Oy samples in magnetic fields up to 1.7 T. Features in the temperature derivative of the resistivity curves were associated with the presence of a superconducting transition between superconducting grains, coupled by weak links with a distribution of critical currents and critical temperatures, and the superconducting transition within grains. The transition between grains was more strongly suppressed in temperature with the application of a magnetic field in samples with weaker coupling between grains. The presence of a transition in a magnetic field due to weak links between grains was verified at 77 K by the observation of a current dependent resistivity in a magnetic field. 相似文献
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X-ray powder diffraction, magnetic susceptibility and electrical resistivity measurements have been used to investigate the effect of Sn substitution in the Bi1.7Pb0.3Sr2Ca2(Cu3−xSnx1.2Oy system for different values of Sn concentrationx(0×1.33). The substitution of Sn is found to decrease the superconducting volume fraction of the 2223 phase. The 2212 phase is enhanced until it reaches a maximum at x=0.67. The system has a complete 2212 phase at x=0.88. An increase in the normal-state resistivity with a corresponding suppression of the temperature at which the resistivity goes to zero is observed with increasing x for the samples which are superconducting. The substitution of Sn probably causes a spatial disorder in the CuO2 planes, which in turn enhances the Coulomb interaction. Samples with x1.0 are found to be insulating. 相似文献
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Y.D. Zhao Jonghyurk Park R.-J. Jung H.-J. Noh S.-J. Oh 《Journal of magnetism and magnetic materials》2004,280(2-3):404-411
We have investigated the structural, magnetic and transport properties of La1−xBixMnO3 samples. As the Bi content increases, a structural transition from rhombohedral to pseudocubic and a magnetic phase transition from ferromagnetic ordering to cluster glass are identified. Metal–insulator (MI) transitions and large magnetoresistance (MR) effects are observed at low Bi doping levels, while insulating behavior of resistivity is found in the whole measured temperature range at high-doping levels. Two distinct ferromagnetic insulating (FI) states are found at low temperatures in this system. One can be suppressed and the other can be enhanced by applying magnetic fields. Possible reasons for the observed structural, magnetic phase transitions and changes of resistivity behavior with Bi doping are discussed. 相似文献
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RbCr3As3是具有[(Cr3As3)-]∞线性链的准一维超导体,超导转变温度约为6.6 K.对RbCr3As3单晶进行了电输运和极低温热输运性质的研究.低温下,拟合了RbCr3As3正常态电阻率随温度的变化,发现其满足费米液体行为.通过拟合超导转变温度随磁场的关系,得到RbCr3As3单晶的上临界场约为25.6 T.对RbCr3As3进行了零场下的极低温热导率测量,得到其剩余线性项为7.5 μW·K-2·cm-1,占正常态热导率值的24%.测量不同磁场下RbCr3As3的热导率,发现与单带s波超导体相比较,RbCr3As3剩余线性项随磁场增加相对较快.这些结果表明RbCr3As3单晶很可能是有节点的非常规超导体. 相似文献
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W. Goldacker M. Quilitz B. Obst H. Eckelmann 《Physica C: Superconductivity and its Applications》1998,310(1-4):182-186
Hysteresis losses and coupling losses, a main component of the AC losses in Bi(2223) tapes, can effectively be reduced by enhancing the resistivity of the matrix material between the filaments and applying a filament twist. Since through alloying the sheath, as using AgAu(8 wt.%), the resistivity can only be raised by a factor <10 (77 K), a new conductor configuration with a quite novel composite matrix having resistive SrCO3 barriers inside the Ag matrix between the filaments was developed. These new barriers, a cheap and commercial material, withstand the tape annealing, do not react with the superconductor, sinter dense and have a good bonding to Ag. Applying two different preparation techniques for 19 filament prototype tapes, critical current densities up to 20.7 kA cm−2 were achieved. We report on tape preparation, the effect on the phase texture and the superconducting properties of such barrier tapes. 相似文献
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M.A. Crusellas J. Fontcuberta S. Piol T. Grenet J. Beille 《Physica C: Superconductivity and its Applications》1991,180(5-6):313-323
Measurements of the in-plane and c-axis normal-state resistivity in a superconducting Nd1.85Ce0.15CuO4−δ single crystal are reported. The resistivity anisotropy of this n-type material is ≤250, much smaller than BiSCCO and comparable to YBaCuO. Both, ab(T) and c(T) displays a metallic-like positive temperature coefficient of resistivity with a basic T2 dependence. We discuss some possible origins of this peculiar temperature dependence. 相似文献
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Intrinsic tunneling spectroscopy in high magnetic field (H) is used for a direct test of superconducting features in the quasiparticle density of states of pure Bi2212 and intercalated HgBr2-Bi2212 high- T(c) superconductors. We were able to distinguish with great clarity two coexisting gaps: (i) the superconducting gap, which closes as H-->H(c2)(T), and (ii) the c-axis pseudogap, which does not change either with H or with T. Strikingly different H dependencies, together with previously observed different temperature dependencies of the two gaps, speak against a superconducting origin of the pseudogap. 相似文献
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We have systematically studied the behaviors of the resistivity and magnetization of CeSb_2 single crystals as a function of temperature and external field. Four anomalies in the resistivity/magnetization-versus-temperature curves are observed at low magnetic field. They are located at 15.5 K, 11.5 K, 9.5 K, and 6.5 K, corresponding to the paramagnetic–magnetically ordered state(MO), MO-antiferromagnetic(AFM), AFM–AFM, and AFM–ferromagnetic(FM) transitions, respectively.The anomaly at 9.5 K is only visible with H‖[010] by magnetic susceptibility measurements, indicating that the AFM–AFM transition only happens along [010] direction in ab-plane. The four magnetic transitions are strongly suppressed by high external field. Finally, the field-temperature phase diagrams of CeSb_2 with different orientations of the applied field in ab-plane are constructed and indicate the highly anisotropic nature of the magnetization of CeSb_2. 相似文献
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Fermi–Dirac statistics has been utilized by introducing the average ionization energy (EI) as an additional anomalous energy gap in order to derive the two-dimensional concentration of charge carriers and the phenomenological resistivity model for the superconducting polycrystalline materials. The best fitted values of EI and the charge carriers' concentration ranges in the vicinity of 4 to 9 meV and 1016 m−2, respectively, for the superconducting single crystal samples and polycrystalline compounds synthesized with various compositions via solid-state reactions. The phenomenological resistivity model is further redefined here based on the gapless nature of charge-carriers' dynamics within the Cu---O2 planes that corresponds to anomalous Fermi liquid behavior, which is in accordance with the nested Fermi liquid theory. 相似文献
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Jan Vogel Maurizio Sacchi Ronald J. H. Kappert John C. Fuggle Jeroen B. Goedkoop Nicholas B. Brookes Gerrit van der Laan Ernesto E. Marinero 《Journal of magnetism and magnetic materials》1995,150(3):293-303
We have used linearly and circularly polarized X-rays to determine the magnetic properties of several TbxFe1−x amorphous films. Absorption measurements on the M4.5 edges of Tb and the L2.3 edges of Fe allowed us to obtain information about the size and direction of local magnetic moments. Our results confirm that linear dichorism in rare earth M4.5 edges can give useful information about both crystal field and magnetic effects. 相似文献
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L. M. Paulius B. W. Lee M. B. Maple P. K. Tsai 《Physica C: Superconductivity and its Applications》1994,230(3-4):255-262
We present a reliable method for growing single crystals of Y1−xPrxBa2Cu3O7−δ high-Tc superconductors in ZrO2 crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al2O3 crucibles. We describe techniques for crystal growth in both Al2O3 and ZrO2 crucibles using an excess of BaCo3 and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant. 相似文献
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H. Claus U. Gebhard G. Linker K. R hberg S. Riedling J. Franz T. Ishida A. Erb G. Mü ller-Vogt H. Wü hl 《Physica C: Superconductivity and its Applications》1992,200(3-4):271-276
X-ray diffraction, resistivity, AC and DC magnetization data on high-quality single crystals of YBa2Cu3O7−δ are presented. We demonstrate that for δ<0.08, the (0 0 l) diffraction lines are split into two, indicating that at these high oxygen concentrations the crystals are no longer single phase but actually consist of two (or more) different phases with slightly different c-axis parameters. In the two-phase region, the electrical resistivity and the AC and DC magnetic susceptibilities show a broadening of the superconducting transition. This broadening is thought to be due to the proximity effect or strains in two finely dispersed phases with slightly different transition temperatures. 相似文献
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Soon-Gil Jung W.K. Seong W.N. Kang Eun-Mi Choi Heon-Jung Kim Sung-Ik Lee Hyeong-Jin Kim H.C. Kim 《Physica C: Superconductivity and its Applications》2006,450(1-2):114-117
The Hall resistivity (ρxy) and the longitudinal resistivity (ρxx) in c-axis-oriented superconducting MgB2 thin films have been investigated in extended fields up to 18 T. We have observed a scaling behavior between the Hall resistivity and the longitudinal resistivity, , where the exponent (β) is observed to be independent of the temperatures and the magnetic fields. For a wide magnetic field region from 1 to 18 T and a wide temperature region from 10 to 28 K, a universal power law with β = 2.0 ± 0.1 was observed in c-axis-oriented MgB2 thin films. These results can be well interpreted by using recent models. 相似文献
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铁基超导体中含有一类特殊的112型结构化合物,其层状结构中含有一层锯齿形的As链构型.本文报道了用CsCl助熔剂法生长新型铁基112型EuFeAs2母体单晶的具体方法,以及对该单晶的结构和物性的详细表征.通过能量色散X射线能谱扫描对单晶样品进行的化学成分分析,以及单晶X射线衍射的结构解析,确定该单晶样品属于EuFeAs2相,结构精修得到EuFeAs2具有空间群为Imm2(No.44)的正交晶体结构,晶格常数分别是a=21.285(9)Å,b=3.9082(10)Å,c=3.9752(9)Å.通过低温电阻测量,发现在110 K附近和46 K附近存在两个异常电阻跳变.进一步分析表明,110 K附近存在两个邻近的相变,这两个相变与铁基母体材料中常见的结构相变和Fe2+的反铁磁相变相符合.结合磁化率测量分析,可知46 K附近的相变属于Eu2+的反铁磁相变. 相似文献
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A. Villaume A. Antonevici D. Bourgault L. Porcar 《Physica C: Superconductivity and its Applications》2009,469(2-3):120-125
Magneto-optical (MO) imaging was used to study and characterize superconducting Bi2212 multifilaments melted in a 5 T magnetic field. MO investigations were performed in presence of a transport current, with and without the superposition of an external magnetic field (30 mT). Transport current redistributions via the Ag cladding have been observed in MO self-field experiments for the first time in Bi2212 multifilaments. MO in situ investigations under tensile stress reveal a slow progression of the cracks, that do not cross the entire section of the multifilamentary tape. This crack formation is correlated with the transport critical current versus strain curves: the critical current drop under tensile stress is relatively smooth for Bi2212 multifilaments. 相似文献
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为了及时的发现和保护超导体在失超过程中由于局部温度的突然升高而导致的材料的不可逆破坏行为,对于超导材料的失超行为深入地研究和定量地分析是必要的. 本文结合电场方程和热平衡方程, 建立了能够描述失超行为的热-电耦合方程, 并构建了能够表征多芯 Bi2212 圆线材结构的三维模型, 同时基于有限单元法进行数值计算, 研究其失超 行 为. 通过对比实验与研究结果验证模型的准确性和有效性, 继而研究了正常区传播速度(NZPV) 和最小失超能( MQE) 与运输电流之间的关系, 并给出了热失超过程中电流重分布过程. 相似文献
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Vilas Shelke H. S. Tewari N. K. Gaur R. K. Singh 《Physica C: Superconductivity and its Applications》1998,300(3-4):217-224
We have investigated the effect of Hg addition on the superconducting properties of BiSrCaCuO system. Polycrystalline samples with nominal composition Bi2Sr2−xHgxCa1Cu2Oy and Bi2Sr2−xHgxCa2Cu3Oy (x=0.3) were synthesized and used to investigate the phase evolution by XRD, superconducting behaviour by R–T measurement and the structural grain boundary effects by SEM. From these measurements, it has been noticed that the phases obtained with both types of compositions are the same as Bi2212 but the Tc values are different. With additional annealing, Tc zero values were raised from 60 to 72 K in Bi2Sr2−xHgxCa1Cu2Oy and 64 to 92 K in Bi2Sr2−xHgxCa2Cu3Oy. Also, an improved grain boundary linkage has been observed by SEM for the 92 K sample. 相似文献