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Author (up) Civale, L.; Pasquini, G.; Levy, P.; Nieva, G.; Casa, D.; Lanza, H. openurl 
  Title Time relaxation of persistent currents in YBa2Cu3O7−x crystals with columnar defects Type Journal Article
  Year 1996 Publication Physica C: Superconductivity Abbreviated Journal Physica C  
  Volume 263 Issue 1-4 Pages 389-395  
  Keywords  
  Abstract We have measured the persistent currents and their time relaxation in YBa2Cu3O7−x single crystals with correlated disorder introduced by irradiation with high-energy heavy-ions. For vortex density lower than the defect density, and for applied fields either parallel or nonparallel to the columnar defects, we find clear evidence of a pinning-crossover between a regime of strong individual pinning at low temperatures and a regime of weaker collective pinning at high temperatures. We explore the vortex dynamics above and below this crossover.  
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  Call Number BT @ gnieva @ Serial 455  
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Author (up) Civale, L.; Pasquini, G.; Levy, P.; Nieva, G.; Lanza, H. isbn  openurl
  Title AC susceptibility of pinned vortices in YBa2Cu3O7 crystals with correlated disorder Type Journal Article
  Year 1996 Publication Advances in Superconductivity: VIII: Proceedings of the 8th International Symposium on Superconductivity Abbreviated Journal  
  Volume Issue Pages 553  
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  Publisher Springer-Verlag Place of Publication Tokyo Editor Hayakawa, Hisao; Enomoto, Y.;  
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  ISSN ISBN 4431701834 Medium  
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  Notes Approved no  
  Call Number BT @ gnieva @ Serial 460  
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Author (up) Curiale, J.; Sánchez, R.D.; Troiani, H.E.; Pastoriza, H.; Levy, P.; Leyva, A.G. openurl 
  Title Morphological and magnetic characterization of manganites oxide based nanowires and nanotubes Type Journal Article
  Year 2004 Publication Physica B Abbreviated Journal  
  Volume 354 Issue 1-4 Pages 98-103  
  Keywords  
  Abstract A morphological and magnetic study of sub-micrometric nanostructures of a manganese oxide-based compound La0.325Pr0.300Ca0.375MnO3 is presented. Nanowires of 50 and 100 nm and tubes with external diameters of 200 and 800 nm were synthesized. Scanning electron microscopy with EDS microanalysis (SEM) and transmission electron microscopy (TEM) allowed to characterize the morphology and microstructure of these nanostructures. The walls of the nanotubes are composed of on average 40 nm grain size particles, while in nanowires the grains are much smaller, in the range between 4 and 20 nm. In both situations, the small grains present a random crystalline orientation, as it is confirmed by TEM diffraction experiments. Magnetization measurements and hysteresis loops are presented and discussed based on magnetic interaction between the grains, anisotropy considerations and reversal magnetization mechanisms.  
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  Call Number BT @ hernan @ curiale04 Serial 10  
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Author (up) Curiale, J.; Sánchez, R.D.; Troiani, H.E.; Ramos, C.A.; Pastoriza, H.; Leyva, A.G.; Levy, P. openurl 
  Title Magnetism of manganite nanotubes constituted by assembled nanoparticles Type Journal Article
  Year 2007 Publication Phys. Rev. B Abbreviated Journal  
  Volume 75 Issue Pages 224410  
  Keywords  
  Abstract We present the study of the magnetic properties of manganite nanotubes with 800 nm of external diameter and 3-5 μm length. The study includes two ferromagnetic compounds, La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3, and one with ferromagnetic and charge ordered phase coexistence, La0.325Pr0.300Ca0.375MnO3. In this case, the walls are formed by grains and have approximately thickness of 150 nm and the most probable grain size is 70 nm. For the ferromagnetic nanotubes smaller values are observed, between 45 and 60 nm for the thickness and 25 nm for the grain size, respectively. In La0.325Pr0.300Ca0.375MnO3 we observe distinctive features comparing with the ferromagnetic nanotubes. After cooling below T$_C$ the samples at $H=0$, the first magnetization curve shows a gradual growth of the magnetization until reach a maximum value, which depends of H. After this, the material presents expected ferromagnetic hysteresis loops. Also, significant differences between the cooling and warming magnetization processes and large linewidth in the ferromagnetic resonances are observed. These experimental facts are explained in terms of the competition between the charge ordered and the ferromagnetic phases, including strong interaction among these last regions. Observations of dipolar interactions between the magnetic grains are evidenced by isothermal remanent magnetization and direct current demagnetization experiments.  
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  Call Number BT @ hernan @ curiale07 Serial 11  
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Author (up) Herbsommer, J.A.; Luzuriaga, J.; Civale, L.; Nieva, G.; Pasquini, G.; Lanza, H.; Levy, P. url  openurl
  Title Angular variation of pinning near the irreversibility temperature in single crystal Y Ba2Cu3O7-? with splayed columnar defects Type Journal Article
  Year 1998 Publication Physica C Abbreviated Journal Physica C  
  Volume 304 Issue 1-2 Pages 112-118  
  Keywords Columnar defects; Critical current density; Flux pinning; Pinning force; Anisotropy; Critical current density (superconductivity); Crystal defects; Single crystals; Columnar defects; Flux pinning; Yttrium barium copper oxides  
  Abstract We have studied vortex pinning through ac susceptibility measurements in single crystals of YBCO with columnar defects (CDs). The CDs have 0, 10 and 20 splay angle and average direction 108 off the c-axis. By studying the angular variation we can compensate for the anisotropy and effects of twins, etc. Using a simple expression we can obtain the angular spread when the field direction is outside the splay angle. An increase of pinning when the field direction is inside

the angle defined by the CDs can be attributed to vortex entanglement due to the splay and the suppression of the sliding of double kinks.
 
  Address Departamento de F  
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  ISSN 09214534 (ISSN) ISBN Medium  
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  Notes Cited By (since 1996): 10; Export Date: 28 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Herbsommer, J.A.; Ctro. Atom. Bariloche Inst. Balseiro; CNEA and UNC 8400 Bariloche, Argentina; References: Civale, L., Marwick, A.D., Worthington, T.K., Kirk, M.A., Thompson, J.R., Krusin-Elbaum, L., Sun, Y., Holtzberg, F., (1991) Phys. Rev. Lett., 67, p. 648; Hwa, T., Doussal, P.L., Nelson, D.R., Vinokur, V.M., (1993) Phys. Rev. Lett., 71, p. 3545; Civale, L., Krusin-Elbaum, L., Thompson, J.R., Wheeler, R., Marwick, A.D., Kirk, M.A., Sun, Y.R., (1994) Phys. Rev. B, 50, p. 4102; Krusin-Elbaum, L., Thompson, J.R., Wheeler, R., Marwick, A.D., Li, C., Patel, S., Shaw, D.T., Ullmann, J., (1994) Appl. Phys. Lett., 64, p. 3331; Hardy, V., Whal, A., Hebert, S., Ruyler, A., Provost, J., Groult, D., Simon, C., (1996) Phys. Rev. B, 54, p. 656; Hardy, V., Ruyter, A., Whal, A., Maignan, A., Groult, D., Provost, J., Simon, C., Noel, H., (1996) Physica C, 257, p. 16; Krusin-Elbaum, L., Marwick, A.D., Wheeler, R., Feild, C., Vinokur, V.M., Leaf, G.K., Palumbo, M., (1996) Phys. Rev. Lett., 76, p. 2563; Prozorov, R., Konczykowski, M., Schmidt, B., Yeshurun, Y., Shaulov, A., Villard, C., Koren, G., (1996) Phys. Rev. B, 54, p. 15530; De La Cruz, F., L Approved no  
  Call Number BT @ luzuriag @ Serial 517  
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Author (up) Niebieskikwiat, D.; Silhanek, A.; Civale, L.; Nieva, G.; Levy, P.; Krusin-Elbaum, L. openurl 
  Title Suppression of matching field effects by splay and pinning energy dispersion in YBa2Cu3O7 with columnar defects Type Journal Article
  Year 2001 Publication PHYSICAL REVIEW B Abbreviated Journal  
  Volume 63 Issue 14 Pages 144504  
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  Abstract We report measurements of the irreversible magnetization M-i of a large number of YBa2Cu3O7 single crystals with columnar defects (CD). Some of them exhibit a maximum in M-i when the density of vortices equals the density of tracks, at temperatures above 40 K. We show that the observation of these matching field effects is constrained to those crystals where the orientational and pinning energy dispersion of the CD system lies below a certain threshold. The amount of such dispersion is determined by the mass and energy of the irradiation ions, and by the crystal thickness. Time relaxation measurements show that the matching effects are associated with a reduction of the creep rate, and occur deep into the collective pinning regime.  
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  ISSN 0163-1829 ISBN Medium  
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  Notes ISI:000168059800084 Approved no  
  Call Number BT @ hernan @ Serial 217  
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Author (up) Pasquini, G.; Levy, P.; Civale, L.; Nieva, G.; Lanza, H. doi  openurl
  Title Linear response in the AC susceptibility of vortices in YBa2Cu3O7 crystals with columnar defects Type Journal Article
  Year 1997 Publication Physica C: Superconductivity Abbreviated Journal  
  Volume 274 Issue 1-2 Pages 165-172  
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  Abstract We explore the AC magnetic susceptibility of YBa2Cu3O7 single crystals with columnar defects. For vortices parallel to the defects the linear response is mainly determined by the Campbell penetration depth with a field independent Labusch parameter indicating that vortices are individually pinned. The small dissipation in this limit is likely to arise from thermal fluctuations of vortex segments between pairs of metastable states (two-level systems) in the Bose glass phase. Tilting vortices away from the tracks results in a reduction of the Bose glass temperature and an increase of the dissipation due to the reduction of the pinning forces. We discuss the onset of nonlinear response as the AC field increases.  
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  ISSN 0921-4534 ISBN Medium  
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  Notes ISI:A1997WG88200021 Approved no  
  Call Number BT @ hernan @ Serial 243  
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Author (up) Righi, E.F.; Grigera, S.A.; Lopez, D.; Nieva, G.; delaCruz, F.; Civale, L.; Pasquini, G.; Levy, P. openurl 
  Title Enhancement of c-axis vortex correlation by twin boundaries and columnar defects in YBa2Cu3O7-delta Type Journal Article
  Year 1997 Publication PHYSICAL REVIEW B Abbreviated Journal  
  Volume 55 Issue 9 Pages 5663-5665  
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  Abstract We report on transport measurements using the flux transformer configuration in a twinned single crystal of YBa2Cu3O7-delta with columnar defects. The vortex liquid shows velocity correlation along the c axis (the direction of the applied magnetic field and the columnar defects) at temperatures that correspond to an uncorrelated liquid in unirradiated samples of the same thickness. These results and previous work about the effect of twin boundaries on vortex velocity correlation show that phase coherence in the field direction is not an intrinsic property of vortex liquids but one induced by extended defects.  
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  ISSN 0163-1829 ISBN Medium  
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  Notes ISI:A1997WN21800036 Approved no  
  Call Number BT @ hernan @ Serial 242  
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Author (up) Silhanek, K.; Guimpel, J.; Civale, L.; Lanza, H.; Levy, P. openurl 
  Title Thickness effects on the pinning by columnar defects Type Journal Article
  Year 2000 Publication PHYSICA C Abbreviated Journal  
  Volume 341 Issue Pages 1217-1218  
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  Abstract We compare the angular dependence of the pinning of equivalent columnar defects in GdBa2Cu2O7 thin films and a thicker YBa2Cu3O7 single crystal. The tracks' related enhancement of the critical currents is much smaller for the case of the thin films. We interpret this thickness dependence as resulting from a competition between the pinning of the correlated structures, related to total sample thickness, and surface boundary conditions, which force the vortices to depin from the columnar defects near the sample surface.  
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  ISSN 0921-4534 ISBN Medium  
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  Notes ISI:000165855700208 Approved no  
  Call Number BT @ hernan @ Serial 175  
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