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用SQUID磁强计测得了Y0.8Pr0.2Ba2Cu3O7-δ单晶在外场平行于c轴条件下的磁化强度随温度的变化。在超导转变下,除了磁化强度是可逆的以外,由于磁通涨落而导致的磁化强度交叉发生在超导转变温度以下约2K处。利用Hao-Clem模型拟合可逆磁化强度得到了热力学临界场Hc(T)和金兹堡-朗道参数k。其它超导参数由Hc(T)和k推得,比较YBa2Cu3O7-δ的热力学参数,讨论了Pr离子的效应 相似文献
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本文采用固相反应法制备了一系列纳米Pr6O11掺杂的MgB2超导块材,掺杂量分别为0,1,3,5,10wt.%.X射线衍射结果表明:随着Pr6O11掺杂量的增加,MgB2的晶格常数也逐渐增大,也就是说Pr原子部分替代了MgB2晶格中的Mg原子.磁测量结果显示,Pr6O11的掺杂对MgB2的超导转变温度(Tc)有很小的抑制.在低含量Pr6O11掺杂(1wt.%)时,MgB2的临界电流密度(Jc)和不可逆场(Hirr)均有明显的提高,但进一步提高Pr6O11的掺杂量时,会损害MgB2在高场下的性能.文中同时也讨论了Pr6O11掺杂影响MgB2的Tc和Jc性能的机理. 相似文献
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本采用Newton迭代法解决了无限长各向异性HTSC导线临界电流密度的自场效应,设临界电流密度平行于x轴,外场与y轴成θ角。我们给出了零外场下,临界电流密度及其自场的空间分布,计算了平均临界电流密度与θ角和外场数值的关系,发现并讨论了自场尺寸效应中的极值问题。我们的方法将可以有效地推广到其他更复杂形状和性质的样品中。 相似文献
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颗粒超导体临界电流密度的尺寸效应 总被引:1,自引:1,他引:0
假设颗粒超导体内某点临界电流密度是该处磁场强度平均值的某种函数,计算了其实测临界电流密度与样品尺寸的关系.发现对目前实验中所用的烧结样品,实验测得的 YBaCuo超导体的临界电流密度有显著的尺寸效应. 相似文献
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The peak effect (PE) in the critical current density in both low and high temperature superconductors has been the subject
of a large amount of experimental and theoretical work in the last few/several years. In the case of YBCO, crucial discussions
describing a dynamic or a static picture are not settled. In that region of field and temperature the mobility of the vortex
lattice (VL) is found to be dependent on the dynamical history. Recently we reported evidence that the VL reorganizes and
accesses to robust VL configurations (VLCs) with different effective pinning potential wells arising in response to different
system histories. One of the keys to understand the nature of the PE is to investigate the VL behavior in the vicinity of
the various VLCs in the region of the PE. The stability of these VLCs was investigated and it was found that they have distinct
characteristic relaxation times, which may be related to elastic or plastic creep processes. In this paper we review some
of these results and propose a scenario to describe the PE in YBCO crystals. 相似文献
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CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
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We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu2 and 2H-NbS2. 2H-NbS2 is iso-structural and iso-electronic to 2H-NbSe2, whose similarity with CeRu2 as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We
report on the step change in equilibrium magnetization across the peak effect in CeRu2. We also present the vortex phase diagram of 2H-NbS2 obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS2 and 2H-NbSe2. 相似文献
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Alok K. Jha 《Journal of magnetism and magnetic materials》2010,322(18):2653-2657
Magnetization studies of YBCO:BaZrO3 composite superconductor have been done over a wide range of temperature and applied magnetic field using MPMS SQUID VSM and the results are compared with that of pure YBCO. The analysis of the observed results indicate that there is considerable improvement in the values of critical current density (JC) and pinning force density (Fp) of YBCO:BaZrO3 composite samples as compared to pure YBCO sample in the entire investigated range of applied magnetic field and temperatures ranging from 4 to 77 K. The variation of JC with reduced temperature t (=T/TC) for the composite samples has been found to be similar to that of pure YBCO sample indicating similar nature of the vortex interaction with pinning centres in both pure and composite samples. The enhancement in the value of JC and Fp in the composite samples as compared to pure YBCO sample has been attributed to the increased defect density in the composite samples due to the presence of BZO particles in YBCO matrix. 相似文献
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S. Kawai E.S. Otabe M. Kiuchi T. Matsushita T. Nomura H. Yamauchi T. Motohashi S. Okayasu 《Physica C: Superconductivity and its Applications》2009,469(15-20):1224-1228
Critical current density was measured for oxygen-controlled (Bi, Pb)-2223 single crystals before and after the irradiation with gold ions in a magnetic field parallel to the irradiation-induced defects along the c-axis. Eleven specimens prepared in different annealing conditions were measured. The condensation energy density of each specimen was evaluated from the observed critical current density by using the summation theory of pinning forces of columnar defects and the flux creep theory. It was found that the specimen heat-treated at 1 atm in oxygen atmosphere has the highest condensation energy density among all specimens. Hence, it is speculated that the optimum oxygen pressure for the anneal is around 1 atm. 相似文献
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T. Egi J. G. Wen K. Kuroda H. Mori H. Unoki N. Koshizuka 《Physica C: Superconductivity and its Applications》1996,270(3-4):223-230
We have studied the superconducting properties of Nd(Ba1−xNdx)2Cu3O7−δ (Nd123, x ≈ 0.1) single crystals grown by the traveling-solvent floating-zone method under 0.1% O2 in Ar atmosphere. The enhancement of the magnetization with increasing field is observed in the hysteresis (M-H) loop in fields both parallel and perpendicular to the c-axis of the Nd123 single crystals as well as in the bulk crystals prepared by the oxygen-controlled-melt-growth (OCMG) method. The composition variation of Ba/Nd is observed in the matrix of Nd123 crystals by an analytical TEM equipped with a cold field-emission gun. It turns out that the enhancement is due to the field-induced pinning effect ascribed to the weak superconducting Nd---Ba substitution regions in the Nd123 matrix. 相似文献
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The temperature and size dependence of the transport critical current in Y-123 and Bi-2223 + Bi-2212 HTSC ceramic sample has been studied. It is shown that the critical current may be presented as power function of cross section area, the critical current density is homogeneous function of coordinates and a number of properties of the critical current density are reported. 相似文献
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Molybdenite crystals used in the present work were grown by direct vapour transport or sublimation method. The electrical
resistivities and I-V characteristics were measured at different temperatures in the symmetry plane. The room temperature
resistance of a specimen annealed for different periods has also been measured. These results are described and discussed. 相似文献
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G. Krabbes G. Fuchs P. Schtzle S. Gruß J. W. Park F. Hardinghaus G. Stver R. Hayn S. -L. Drechsler T. Fahr 《Physica C: Superconductivity and its Applications》2000,330(3-4):181-190
The previously introduced modified melt crystallization process (MMCP) has been applied to prepare single grain YBCO bulk material with Zn partially substituting for Cu. Hole doping was controlled by an appropriate oxidizing treatment of the as-grown bulk. A field induced pinning was indicated by a well pronounced peak of the critical current density jc in the jc vs. H relationship for the maximal oxidized (overdoped) material containing Zn, whereas pure overdoped YBCO shows no peak effect. The peak effect for Zn-doped YBCO appearing for T=77 K at a relatively high field of about 3 T can be attributed to pair breaking by locally induced magnetic moments due to in plane Zn for Cu substitution. Besides high quality of the bulk YBCO, the peak effect is the reason for the trapped field as large as 1.12 T at 77 K in the cylinder of only 25 mm in diameter. 相似文献
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XING Jie GUO ErJia & LU HuiBin School of Materials Sciences Technology China University of Geosciences Beijing China National Laboratory of Mineral Materials Beijing National Laboratory for Condensed Matter Physics 《中国科学:物理学 力学 天文学(英文版)》2011,(8)
The fast-response ultraviolet (UV) photoelectric effect in ZrO2 single crystals with interdigitated electrodes has been investigated experimentally at room temperature. The photovoltage of ZrO2 single crystals exhibits a linear dependence on applied bias and light power density. The photocurrent responsivity to the UV light with a wavelength of 253.65 nm is 9.8 mA/W. For the photovoltaic pulse, a rise time of 501 ps and a full width at half maximum of 1.5 ns have been obtained, when the ZrO2 single crystal ... 相似文献