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Author (up) Gao, Z.X.; Osquiguil, E.; Maenhoudt, M.; Wuyts, B.; Libbrecht, S.; Bruynseraede, Y. url  openurl
  Title 3D-2D dimensional crossover in YBa2Cu3O7 films Type Journal Article
  Year 1993 Publication Physical Review Letters Abbreviated Journal  
  Volume 71 Issue 19 Pages 3210-3213  
  Keywords  
  Abstract We show that, in fully oxidized YBa2Cu3O7 c-axis oriented films, the changes induced in the angular and field dependence of the magnetoresistivity ?ab by increasing the temperature towards Tc are similar to those caused by a lowering in oxygen content. This remarkable behavior can be interpreted as due to a crossover from a three-dimensional to a two-dimensional system as T approaches Tc. Moreover, our critical current data mimic the behavior observed by Qi Li et al. in YBa2Cu3O7/(PrxY1-x)Ba2Cu3O7 multilayers, suggesting the possibility that chain planes are superconducting.  
  Address Laboratorium Voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium  
  Corporate Author Thesis  
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  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 00319007 (ISSN) ISBN Medium  
  Area Expedition Conference  
  Notes Cited By (since 1996): 7; Export Date: 17 April 2009; Source: Scopus; doi: 10.1103/PhysRevLett.71.3210; Language of Original Document: English; Correspondence Address: Gao, Z.X.; Laboratorium Voor Vaste Stof-Fysika en Magnetisme; Katholieke Universiteit Leuven; Celestijnenlaan 200D B-3001 Leuven, Belgium Approved no  
  Call Number BT @ osquigui @ Serial 400  
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Author (up) Griessen, R.; Wen Hai-Hu; Van Dalen, A.J.J.; Dam, B.; Rector, J.; Schnack, H.G.; Libbrecht, S.; Osquiguil, E.; Bruynseraede, Y. url  openurl
  Title Evidence for mean free path fluctuation induced pinning in YBa2Cu3O7 and YBa2Cu4O8 films Type Journal Article
  Year 1994 Publication Physical Review Letters Abbreviated Journal  
  Volume 72 Issue 12 Pages 1910-1913  
  Keywords  
  Abstract The critical current jc and the pinning energy Uc have been determined for three types of yttrium-based superconducting films from current js and dynamic relaxation Q=d lnjs/d ln(dB/dt) data by means of the generalized inversion scheme. For B<2 T and T<80 K the temperature dependence of jc and Uc for all films is found to be in excellent agreement with a model of single vortices pinned by randomly distributed weak pinning centers via spatial fluctuations of the charge carrier mean free path. Pinning due to spatial fluctuations of Tc is not observed.  
  Address Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, 4001-Leuven, Belgium  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 00319007 (ISSN) ISBN Medium  
  Area Expedition Conference  
  Notes Cited By (since 1996): 103; Export Date: 17 April 2009; Source: Scopus; doi: 10.1103/PhysRevLett.72.1910; Language of Original Document: English; Correspondence Address: Griessen, R.; Faculty of Physics and Astronomy; Free University 1081 HV Amsterdam, Netherlands Approved no  
  Call Number BT @ osquigui @ Serial 389  
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Author (up) Libbrecht, S.; Osquiguil, E.; Bruynseraede, Y. url  openurl
  Title Influence of field inhomogeneity on the magnetization of YBCO films Type Journal Article
  Year 1994 Publication Physica C: Superconductivity and its applications Abbreviated Journal Phys C Supercond Appl  
  Volume 225 Issue 3-4 Pages 337-345  
  Keywords Magnetization; Superconducting films; SQUID magnetometers; Superconducting ceramics; YBCO superconductors; High temperature superconductors  
  Abstract DC magnetization data of superconducting thin YBCO films, measured by means of a magnetometer in which the sample is pulled through a set of pick-up coils, are often calculated from pick-up signals which clearly deviate from the ideal response. We show how these signal distortions influence the values obtained for the magnetization, and present a simple model that enables one to simulate the temperature dependence of these distorted pick-up signals, in the case of low-field magnetization measurements. The model is based on the magnetic field inhomogeneity of the magnetometer, in combination with the hysteretic magnetization of the superconducting sample. Optimum values for the model parameters are derived and discussed.  
  Address Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 09214534 (ISSN) ISBN Medium  
  Area Expedition Conference  
  Notes Cited By (since 1996): 11; Export Date: 17 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Bruynseraede, Y.; Laboratorium voor Vaste Stof-Fysika en Magnetisme; Katholieke Universiteit Leuven; Celestijnenlaan 200 D B-3001 Leuven, Belgium Approved no  
  Call Number BT @ osquigui @ Serial 394  
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Author (up) Libbrecht, S.; Osquiguil, E.; Wuyts, B.; Maenhoudt, M.; Gao, Z.X.; Bruynseraede, Y. url  openurl
  Title Effect of room temperature annealing on the properties of oxygen- deficient YBa2Cu3Ox films Type Journal Article
  Year 1993 Publication Physica C: Superconductivity and its applications Abbreviated Journal Phys C Supercond Appl  
  Volume 206 Issue 1-2 Pages 51-58  
  Keywords Annealing; Ceramic materials; Hall effect; Superconducting films; Yttrium compounds; Critical current density; Oxide superconductors; Yttrium barium copper oxides; High temperature superconductors  
  Abstract Annealing at room temperature of quenched oxygen-depleted YBa2Cu3Oxn (6.5?xn<6.8) films, produces a clear increase in the critical temperature Tc and current density Jc, while the normal state resistivity ?{variant}xx and Hall coefficient RH decrease as a function of annealing time, indicating an increase in carrier density. The enhancement of the critical current density Jc is more pronounced at high fields and temperatures due to a shift of the irreversibility line, which scales with the increasing Tc. The observed changes are accompanied by corresponding changes in the crystalline structure, which can be related to oxygen ordering effects.  
  Address Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 09214534 (ISSN) ISBN Medium  
  Area Expedition Conference  
  Notes Cited By (since 1996): 11; Export Date: 17 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Libbrecht, S.; Laboratorium voor Vaste Stof-Fysika en Magnetisme; Katholieke Universiteit Leuven; Celestijnenlaan 200D B-3001 Leuven, Belgium Approved no  
  Call Number BT @ osquigui @ Serial 402  
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Author (up) Libbrecht, S.; van Dalen, A.J.J.; Wuyts, B.; Maenhoudt, M.; Gao, Z.X.; Osquiguil, E.; Griessen, R.; Bruynseraede, Y. url  openurl
  Title Magnetic properties of oxygen deficient Yba2Cu3Ox thin films Type Journal Article
  Year 1994 Publication Physica C: Superconductivity and its applications Abbreviated Journal Phys C Supercond Appl  
  Volume 235-240 Issue PART 5 Pages 2889-2890  
  Keywords  
  Abstract We have invesitgated several superconducting properties of oxygen defiecient YBa2Cu3Ox thin films, with oxygen contents ranging from x = 6.55 to x = 7. By means of torque magnetometry, the temperature dependence of the superconducting current dendity js and relaxation rate of the magnetization Q is measured in an (almost perpendicular) applied magnetic induction of 0.6 T. As the oxygen content is reduced, js decreases, whereas Q increases. Both properties are influenced by the decreased dpoing level as well as the enhanced anisotropy of oxygen depleted YBa2Cu3Ox. Using the Generalixed Inversion Scheme derived by Schnak et al. we obtain the current dependence of the activation energy U(f). We show that U(j) is lowered when the oxygen content is reduced.  
  Address Centro At  
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  ISSN 09214534 (ISSN) ISBN Medium  
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  Notes Export Date: 17 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Libbrecht, S.; Laboratorium voor Vaste-Stoffysika en Magnetisme; Katholieke Universiteit B-3001 Leuven, Belgium Approved no  
  Call Number BT @ osquigui @ Serial 387  
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Author (up) Osquiguil, E.; Gao, Z.X.; Maenhoudt, M.; Wuyts, B.; Libbrecht, S.; Bruynseraede, Y. url  openurl
  Title YBa2Cu3Ox: A natural multilayer system with tunable anisotropy Type Journal Article
  Year 1993 Publication Journal of Physics: Condensed Matter Abbreviated Journal  
  Volume 5 Issue 33 A Pages  
  Keywords  
  Abstract The authors report on magnetoresistivity rho ab( theta ,H,T) measurements below Tc in YBa2Cu3Oxn films with differing oxygen content x. The observed variations in the angular and field dependence of rho ab with reduced x indicate a gradual dimensional crossover from an anisotropic 3D to a quasi-2D behaviour. The increasing anisotropy is related to a decrease of the coupling between the Cu2O2 bilayers when oxygen is removed from the Cu1Ox chain-planes.  
  Address Lab. voor Vaste Stof-Fysika en Magnetisme, Katholieke Univ. Leuven, Belgium  
  Corporate Author Thesis  
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  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 09538984 (ISSN) ISBN Medium  
  Area Expedition Conference  
  Notes Cited By (since 1996): 1; Export Date: 17 April 2009; Source: Scopus; Art. No.: 145; doi: 10.1088/0953-8984/5/33A/145; Language of Original Document: English; Correspondence Address: Osquiguil, E.; Lab. voor Vaste Stof-Fysika en Magnetisme; Katholieke Univ. LeuvenBelgium Approved no  
  Call Number BT @ osquigui @ Serial 399  
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Author (up) Van Dalen, A.J.J.; Griessen, R.; Libbrecht, S.; Bruynseraede, Y.; Osquiguil, E. url  openurl
  Title Quantum creep and pinning properties of oxygen-deficient YBa2Cu3Oxn films Type Journal Article
  Year 1996 Publication Physical Review B – Condensed Matter and Materials Physics Abbreviated Journal Phys. Rev. B Condens. Matter Mater. Phys.  
  Volume 54 Issue 2 Pages 1366-1381  
  Keywords  
  Abstract A high sensitivity capacitance torquemeter has been used for a comprehensive investigation of the induced current densities and dynamic relaxation rates in a YBa2Cu3Oxn film with nominal oxygen content varying between xn=6.55 and xn=7.0. The dynamic relaxation rate Q does not extrapolate to zero at T=0 K, indicating the presence of quantum creep. By changing the oxygen content of the film it is possible to investigate the relation between the quantum creep rate Q(0) and the normal-state resistivity pn(0) at low temperature. Although Q(0) increases monotonically with pn, it is found that Q(0) is not proportional to pn(0), in contrast to the predictions of a theory based on dissipative tunneling of collectively pinned single vortices [Blatter et al., Rev. Mod. Phys. 66, 1125 (1994)]. The experimental results imply that in YBa2Cu3O7 quantum creep takes place in a transition regime between Hall tunneling and dissipative tunneling. For lower oxygen contents the quantum creep regime moves towards the dissipative limit. For each oxygen content the characteristic pinning energy Uc(0) at T=0 is obtained by a linear extrapolation to T= 0 K of the T/Q versus T curves. The critical current density jc at T=0 is determined independently by a linear extrapolation of the measured Injs versus T curves. A power-law relation Uc(0)?[jc(0)]p with p? 0.5 is found, indicating single vortex pinning at higher temperatures. This is confirmed by a detailed analysis of the measured current densities and relaxation rates by means of the generalized inversion scheme developed by Schnack et al. [Phys. Rev. B 48, 13 178 (1993)]. For xn? 6.6 at Be= 0.6 T and for xn? 6.7 at Be= 2.0 T the calculated temperature dependence of jc and Uc agrees remarkably well with a model based on three-dimensional single vortex pinning caused by spatial fluctuations in the charge carrier mean free path. At lower oxygen contents and higher magnetic-fields the agreement gradually breaks down due to the increasing importance of thermal fluctuations.  
  Address Montell Polyolefins, Centre Ricerche G. Natta, P. Le P. to G. Donegani 12, 44100 Ferrara, Italy  
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  ISSN 01631829 (ISSN) ISBN Medium  
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  Notes Cited By (since 1996): 27; Export Date: 17 April 2009; Source: Scopus; CODEN: PRBMD; Language of Original Document: English; Correspondence Address: Van Dalen, A.J.J.; Materials Science Division; Argonne National Laboratory Argonne, IL 60439, United States; References: Mota, A.C., Pollini, A., Visani, P., M Approved no  
  Call Number BT @ osquigui @ Serial 383  
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Author (up) van Dalen, A.J.J.; Griessen, R.; Libbrecht, S.; Osquiguil, E.; Bruynseraede, Y. url  openurl
  Title Observation of quantum creep in oxygen deficient YBa2Cu3O7-? at fields up to 7 T Type Journal Article
  Year 1994 Publication Physica C: Superconductivity and its applications Abbreviated Journal Phys C Supercond Appl  
  Volume 235-240 Issue PART 5 Pages 2959-2960  
  Keywords  
  Abstract Superconducting current densities js and dynamic relaxation rates Q ? d ln js/d ln (dBe/dt) in an oxygen deficient YBa2Cu3O7-? epitaxial film were measured as a function of temperature (1.5K < T < Tirr) in magnetic fields up to 7 T by means of high sensitivity capacitance torquemeters. Below 5 K, the relaxation rate remains high and does not extrapolate to Q = 0 at T = 0K. This is associated to the quantum tunneling of vortices through the energy barrier separating two adjacent vortex configurations. In the case of ohmic dissipation the quantum creep rate is proportional to the normal state resistivity ?{variant}n(0) at T = 0 K. In order to check this theoretical prediction we measured Q as a function of the oxygen content of the sample. The quantum creep rate increases systematically with increasing ?{variant}n(0). However, Q remains finite even when ?{variant}n = 0.  
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  ISSN 09214534 (ISSN) ISBN Medium  
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  Notes Export Date: 17 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: van Dalen, A.J.J.; Faculty of Physics and Astronomy; Free University 1081 HV Amsterdam, Netherlands Approved no  
  Call Number BT @ osquigui @ Serial 393  
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Author (up) Vanacken, J.; Libbrecht, S.; Maenhoudt, M.; Van Haesendonck, C.; Osquiguil, E.; Bruynseraede, Y. url  openurl
  Title The magnetic moment relaxation in oxygen-deficient YBa2Cu3Ox Type Journal Article
  Year 1992 Publication Physica C: Superconductivity and its applications Abbreviated Journal Phys C Supercond Appl  
  Volume 197 Issue 1-2 Pages 9-14  
  Keywords Magnetic Measurements – Relaxation; Oxygen – Concentration; Relaxation Processes – High Temperature Effects; Relaxation Processes – Magnetic Field Effects; Magnetic Moment Relaxation; Oxygen Deficiency; Yttrium Barium Copper Oxides; High Temperature Superconductors  
  Abstract The magnetic moment relaxation in polycrystalline YBa2Cu3Oxmaterial has been studied using zero-field-cooled measurements. The temperature dependence of the relaxation rate shows a field-dependent maximum. When the oxygen content is reduced, the maximum shifts towards lower temperatures. This shift is directly related to a decrease of the intragrain critical current density in the oxygen-deficient material, inducing a decrease of the field H* for complete flux penetration. The characteristic activation energies for depinning in the oxygen-deficient material are below 20 meV.  
  Address Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium  
  Corporate Author Thesis  
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  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 09214534 (ISSN) ISBN Medium  
  Area Expedition Conference  
  Notes Export Date: 17 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Vanacken, J.; Laboratorium voor Vaste Stof-Fysika en Magnetisme; Katholieke Universiteit Leuven; Celestijnenlaan 200 D B-3001 Leuven, Belgium Approved no  
  Call Number BT @ osquigui @ Serial 409  
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Author (up) Wuyts, B.; Gao, Z.X.; Libbrecht, S.; Maenhoudt, M.; Osquiguil, E.; Bruynseraede, Y. url  openurl
  Title Growth of particle-free YBa2Cu3O7 films by off-axis sputtering Type Journal Article
  Year 1992 Publication Physica C: Superconductivity and its applications Abbreviated Journal Phys C Supercond Appl  
  Volume 203 Issue 3-4 Pages 235-239  
  Keywords Copper oxides; Film growth; Film preparation; Magnetrons; Particles (particulate matter); Sputter deposition; Substrates; Superconductivity; Thin films; Yttrium compounds; Critical current density; Off axis single target magnetron sputtering; Particle free superconducting films; Yttrium barium copper oxides; Superconducting films  
  Abstract The preparation of good YBa2Cu3O7 thin films is often hindered by the production of non-stoichiometric particles which degrade the superconducting properties of the layer. A systematic study of films prepared by off-axis single target magnetron sputtering shows that the presence of copper-rich particles dramatically decreases the critical current density but does not affect the critical temperature. The formation of these particles can be avoided by carefully adjusting the position of the substrate with respect to the target. Films without off-stoichiometric particles have excellent superconducting properties.  
  Address Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium  
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  ISSN 09214534 (ISSN) ISBN Medium  
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  Notes Cited By (since 1996): 10; Export Date: 17 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Wuyts, B.; Laboratorium voor Vaste Stof-Fysika en Magnetisme; Katholieke Universiteit Leuven; Celestijnenlaan 200 D B-3001 Leuven, Belgium Approved no  
  Call Number BT @ osquigui @ Serial 403  
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