2PO1-70 Application of Material Power Law in Melt-textured YBa₂Cu₃O_7-d

L. Shan 1, A.M. Sun 1, X.N. Xu 1, X. Jin 1, L.J. Shen 2, and C.C. Lam 2. 1 Department of Physics and National Laboratory of Solid State Mircrostructure, Nanjing University, Nanjing 210008, China. 2 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong.

Presenting Author: L. Shan

Low-electric-field E - J curves of YBa₂Cu₃O_7-d were determined from 0.27T to 1.34T at various temperature from 52K to 83K with the magnetic sweeping method by VSM. Using a empirical material power lay E = E_c(J/J_c)ⁿ, we obtained the characteristic pinning potential U₀(T,H) and real critical current density J_c(T,H) by an appropriate definition of E_c. By further investigation on the changing shape of pinning potential well, we interpreted the peak effect of U₀ with temperature in high temperature superconductors (HTSC's).

2PO1-71 Oxygen Doping Effects on the Magnetization of Bi₂Sr₂CaCu₂O_8+d Single Crystalline System in the Mixed State

E.E. Kaul and G. Nieva, Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica, S.C. de Bariloche, 8400 RN, Argentina

Presenting Author: G. Nieva

We present a systematic study of the oxygen overdoping effects on the dc magnetization loops of Bi₂Sr₂CaCu₂O_8+d single crystalline samples. The overdoping is produced by high oxygen pressure (from 1 to 190 bars) annealing at 500° C. The superconducting critical temperature and the c-axis lattice parameter are used to identify the oxygen content of the samples. The dc magnetization loop measurements are performed with the applied magnetic field parallel to the c-axis of the crystals. The characteristic second peak in the magnetization is present for all the investigated oxygen contents. We show that the position of this second peak and the irreversibility field increase monotonously as a function of oxygen doping.

2PO1-72 Flux-pinning of Y/Nd(123) melt-textured sample

A.S. Mahmoud 1, G.J. Russell 1, M.R. Koblischka 2, N. Chikumoto 2, and M. Murakami 2. 1 Advanced Electronic Materials Group, School of Physics, University of New South Wales, NSW 2052 Sydney, Australia. 2 Superconductivity Research Laboratory, International Superconductivity Technology Centre, 1-16-25, Shibaura, Minato-ku, Tokyo 105, Japan.

Presenting Author: A.S. Mahmoud

Flux-pining in Y_0.5/Nd_0.5-(123) melt-textured growth sample that had been doped with excess 20wt.% YNd-(211) and 0.5 wt.% PtO₂ has been analyzed by means of a scaling approach. The different parameters of scaling, irreversibility field (B_irr), magnetic field (B_jp) and currenrt density of the fishtail peak effect, and the field (B_fp) corresponding to the maximum pinning force density (F_p,max), were determined using measurements of magnetically induced current density as a function of field and temperature. For the commonly used scaling of normalized volume pinning forces, (F_p = J_cxB_a)/F_p,max, versus reduced magnetic fields h=B_a/B_irr, (where B_a stands for applied magnetic field), the curves collaps into a universal curve with a peak corresponding to h=0.42. Based on the approach of Dew-Hughes [1], we interpret the position of this peak as a clear indication of a ƒÔT_c-pinning type. Similar scaling was also obtained with the use of B_pf instead of B_irr, while less scaling was obtained with the use of J_p. In this study we present the fitting analysis and compare our results with those for other RE-(123) systems.

2PO1-73 Influence of oxygen deficiency and Nd/Ba substitution on critical currents in Nd_1+xBa_2-xCu₃O_y single crystals

Th. Wolf, H. Kupfer, and P. Schweiss, Forschungszentrum Karlsruhe, Institut für Technische Physik,Postfach 3640, D-76021 Karlsruhe, Germany

Presenting Author: Th. Wolf

2PO1-74 Vortex pinning in (103)/(013) oriented YBCO films

Carlo Camerlingo 1, Ciro Nappi 1, Mauizio Russo 1, and Grzegorz Jung 2. 1 Istituto di Cibernetica del Consiglio Nazionale delle Ricerche, 80072 Arco Felice, Italy. 2 Department of Physics, Ben Gurion University of the Negev, 84105 Beer-Sheva, Israel.

Presenting Author: C. Camerlingo

The electrical and the superconducting properties of (103)/(013) oriented YBCO films were investigated as a function of the angle of incidence of the current with respect to the in-plane orientation of the film lattice. The 150 nm thick films were fabricated by dc inverted cylindrical magnetron on (110) SrTiO₃ substrates. The (103)/(013) lattice orientation was confirmed by X-ray and Raman spectroscopy analysis. The films were patterned in 20 mm wide lines, diverging each other by an angle of 30°, implying different orientations with respect to the substrate crystal axes.

Unidirectional twin boundary defects are expected to occurs in the film, resulting in the observed anisotropy g of the resistivity in normal state (g = 5.5 at T=100K). The current-voltage (V-I) characteristics are also affected by the current direction, due to different vortex pinning involved: The lines directed along the YBCO (100) and (010) axes (angle q=0) exhibit a relatively large critical current density and a V-I dependence similar to that typically observed in c-axis oriented films. Increasing the angle q, the critical current density decreases and the V-I dependence changes distinctly, approaching the behavior expected in systems with planar defects.

Experimental data on the longitudinal and transversal components of the voltage V dependence on the current and on temperature are also reported.

2PO1-75 Detection of broken vortices by influence of remanent magnetic fields on critical current in ceramic HTSC samples

V.F. Khirnyi and A.A. Kozlovskii, Institute for Single Crystals, Lenin Ave. 60, Kharkov 310001, Ukraine

Presenting Author: V.F. Khirnyi

For ceramic YBa₂Cu₃O_x and Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_x samples with small and large pinning forces the dependence of the critical current I_c on the value of trapped magnetic field H was obtained at 77 K under different conditions of sample cooling and magnetic field switching on.

For the samples with small pinning forces placed in the external field H, the critical current I_c^FC measured in FC regime was found to exceed the critical current I_c^ZFC measured in ZFC regime. For samples with large pinning forces I_c^ZFC(H) = I_c^FC(H).

This is explained by the fact that vortices penetrating the sample along the direction of the external magnetic field, were broken on inhomogeneities the size of which was larger than the depth of magnetic field penetration. Therefore the fragments of vortices pinned in granules had scattering fields which partially compensated the external field and affecting the value of critical current. The calculated the remanent magnetic field H_REM values coincide with those determined from the location of maxima on I_c(H) curves obtained in FC regime.

In the present research, the case of the existence of broken quantized vortices formed in ceramic HTSC samples due to their granular structure, is considered for the first time.

2PO1-76 Field and temperature dependence of critical current density of Fe doped Bi2212 single crystals

K.K. Uprety 1, J. Horvat 1, X.L. Wang 1, G.D. Gu 2, H.K. Liu 1, and S.X. Dou 1. 1 Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia. 2 School of Physics, University of New South Wales, Sydney 2052, Australia.

Presenting Author: K.K. Uprety

Critical current density J_c as a function of magnetic field and temperature have been studied in Fe-doped and pure Bi2212 single crystals. The nominal iron content in the Bi_2.1Sr_1.9Ca_1.0(Cu_1-yFe_y)₂O_x single crystal was y = 0.000, 0.005, 0.016 and 0.022. A strong field and temperature dependence of J_c have been observed for the samples with y = 0.022 & 0.016 doping. At zero field, large J_c was observed for these samples up to temperature of 38K, as compared to the samples with y = 0.005 and y = 0.000. However, for T > 38K, samples with y = 0.016 and 0.022 had lower values of J_c than samples with y = 0.000 and 0.005. Similarly, for H < 500 Oe samples with y = 0.000 and 0.005 had lower J_c than the more strongly doped samples. For H > 500Oe, it was the opposite. The samples with y = 0.005 were found to show large J_c in wider range of the temperatures and fields than any other samples. This indicated that the iron in CuO₂ planes acted as an effective pinning center. The effectiveness of the pinning centers was strongly influenced by the field and thermal excitations.

2PO1-77 The electromagnetic properties of the BSCCO 2223/Ag-sheathed tapes prepared with different starting condition precursor powder

Xiao-dong Su 1, Zongquan Yang 1, Ling Hua 1, Gui-wen Qiao 1, Jai-moo Yoo 2, de Boer 3. 1 Institute of Metal Research, Chinese Academy Sciences, Shenyang 110015, China. 2 Korea Institute of Machinery & Materials, 66 Sangnam-Dong, Changwon, Kyungnam 641-010, Korea. 3 Van der Waals-Zeeman InstituteUniversity of AmsterdamValckenierstraat 651018 XE, Amsterdam, The Netherlands.

Presenting Author: X.D. Su

BSCCO 2223 Ag-sheathed tapes were prepared with spray dried precursor powders, which are of different starting condition. Transport critical current J_c of tapes varied from 25-50 kA/cm². The J_c(B) properties were investigated in applied magnetic filed, and magnetic measurement was performed in a superconduting quantum interference device(SQUID) at various temperature between 5K and 77K. Proper explanations were given for the great improvement of J_c in certain tape.

2PO1-78 The Effective Flux Pinning Potential of Ag/Bi-2223 Tapes for H//c-axis

Wu M. Chen 1,2, Hua K. Liu 2, Fei Lin 1, Yuan C. Guo 2, Su S. Jiang 1, Shi X. Dou 2. 1 National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P.R. China. 2 Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong NSW 2522, Australia.

Presenting Author: H.K. Liu

A strong and effective flux pinning potential U_eff is significant for high J_c superconductors, U_eff is theoretically dependent on three physical quantities, critical current density J_c, magnetic field H and temperature T, i.e. U_eff = U_eff(T,H,J). Perhaps, due to its complex, up to now only few research work has been reported, which investigated the function of U_eff(T,H,J) for Bi-2223 superconductors. To determine the U_eff(T,H,J) of Ag/Bi-2223 tapes, measurements of transport current density J(T,H) were performed on applied magnetic field from 0 to 3T and at temperature from 23K to 77K. The field was perpendicular to the broad surface of the tape. Generally, U_eff(T,H,J) is regarded as U_eff(T,H,J) = U(T,H)J(T,H). Since J(T,H), J(T,H) =J(T) J(H), has been determined experimentally, U(T,H) may obtained by fitting the function of J(T,H) if a proper theory of flux dynamics can be used. In the case of transport current density, the experimental J(H) is found to be linear with lnµoH, that conforms to Andson's flux dynamics theory. By using the theory, the effective pinning potential U_eff(T,H,J) for Ag/Bi-2223 tapes is determined and formulated quantitatively. The resulting flux pinning potential U(T,H) is shown in a three dimension diagram.