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Author Pastoriza, H.; Candia, S.; Nieva, G. openurl 
  Title Anisotropic vortex dynamics in twined YBaCuO single crystals Type Journal Article
  Year 2000 Publication Physica B Abbreviated Journal  
  Volume 284-288 Issue 2 Pages 763-764  
  Keywords  
  Abstract Rotating continuously the applied vortex force and measuring the vortex velocity vector, we were able to directly determine the role of twin boundaries in the vortex dynamics in YBa$2$Cu$3Ο_7$ single crystals with unidirectional twins. We show the different effect of these correlated pinning defects into the various vortex phases. In the entangled vortex liquid state, we observe a linear response but with an anisotropic viscosity. On the other hand, an anomalous guided motion by twin planes is found in the vortex solid.  
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  Call Number BT @ hernan @ pastoriza00 Serial 39  
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Author 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  
  Keywords  
  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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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700208 Approved no  
  Call Number BT @ hernan @ Serial 175  
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Author Steren, L.B.; Sirena, M.; Guimpel, J. openurl 
  Title Substrate effect on the magnetic behavior of manganite films Type Journal Article
  Year 2000 Publication JOURNAL OF APPLIED PHYSICS Abbreviated Journal  
  Volume 87 Issue 9 Pages 6755-6757  
  Keywords  
  Abstract The film thickness (t) dependence of the magnetic properties of La0.6Sr0.4MnO3 (LSMO) films grown on (001) MgO and (001) SrTiO3 substrates has been studied. Hysteresis loops measured at low temperature show a smooth increase of the retentivity accompanied by a decrease of the coercitive field as the film thickness increases. The increase of coercitivity with decreasing t can be interpreted in terms of a change in the domain structure of the films mainly due to an augmentation of domain pinning defects. The magnetic anisotropy has been measured using ferromagnetic resonance (FMR). A volume (VA) and a surface (SA) anisotropy contribution have been deduced from FMR angular dependence studies for both series of samples. In the LSMO films grown on MgO a VA component that corresponds to an easy-axis perpendicular to the plane of the films has been found while in contrast, the LSMO films grown on SrTiO3 present an easy-plane anisotropy. The SA is positive for both series favoring a perpendicular magnetic anisotropy. The measured magnetic anisotropy has been assigned to substrate-induced effects. (C) 2000 American Institute of Physics. [S0021-8979(00)55708-9].  
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  ISSN 0021-8979 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000086728800281 Approved no  
  Call Number BT @ hernan @ Serial 178  
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Author Steren, L.B.; Sirena, M.; Guimpel, J. openurl 
  Title Substrate influence on the magnetoresistance and magnetic order in La0.6Sr0.4MnO3 films Type Journal Article
  Year 2000 Publication JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Abbreviated Journal  
  Volume 211 Issue 1-3 Pages 28-34  
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  Abstract We report structural, magnetic and transport measurements on La0.6Sr0.4MnO3 thin films grown on MgO and TiSrO3 substrates with thickness varying from 5 to 500 nm. We find that the lattice mismatch between substrates and films affects the morphology and induced-strains of the films. We show that these two different effects strongly influence the ferromagnetic order, the metal-insulator transition, the localization of the current carriers and the magnetoresistance of these materials. (C) 2000 Elsevier Science B.V. All rights reserved.  
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  Series Volume Series Issue Edition  
  ISSN 0304-8853 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000085772100006 Approved no  
  Call Number BT @ hernan @ Serial 179  
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Author Fasano, Y.; Menghini, M.; de la Cruz, F.; Nieva, G. openurl 
  Title Weak interaction and matching conditions for replicas of vortex lattices Type Journal Article
  Year 2000 Publication PHYSICAL REVIEW B Abbreviated Journal  
  Volume 62 Issue 22 Pages 15183-15189  
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  Abstract We present experiments demonstrating the conditions under which weak interaction between replicas of vortex structures break their translational and rotational symmetry. The Fe clumps introduced by Bitter decorations of vortex structures are used to induce an extremely weak interaction fur subsequent vortex structures in low and high temperature superconducting crystals. The matching between the Fe pattern acid the vortex configuration require the structure to be prepared under quite stringent conditions: The field creating the structure has to be the same in magnitude although it can differ in orientation from that used for the preparation of the Fe pattern. The interaction between vortex replicas as represented by the Fe clumps of Bitter decorations makes it possible to differentiate the vortex nucleation and propagation mechanisms in low and high temperature superconductors.  
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  Series Volume Series Issue Edition  
  ISSN 0163-1829 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165883800075 Approved no  
  Call Number BT @ hernan @ Serial 219  
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Author Correa, V.F.; Herbsommer, J.A.; Kaul, E.E.; de la Cruz, F.; Nieva, G. openurl 
  Title Onset of the 0-dimensional vortex pinning behavior in the optimally doped and overdoped Bi2Sr2CaCu2O8+delta system Type Journal Article
  Year 2000 Publication PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Abbreviated Journal  
  Volume 341 Issue Pages 1285-1286  
  Keywords  
  Abstract We report results of transverse AC magnetic permeability in the linear regime and DC magnetization loops for optimally doped and oxygen overdoped samples of Bi2Sr2CaCu2O8+delta The data cover the low temperature (T < 25K) and low held (H-a < 1000 Oe) region of the magnetic (H-a-T) phase diagram. In optimally doped as well as in overdoped samples a crossover to a O-dimensional pinning regime (Larkin length, L-C(C), shorter than the inter-plane CuO2 distance) is observed at a characteristic temperature Too for all investigated fields. The order-disorder transition, identified by the second peak in magnetization and a non monotonous field dependence of the AC penetration depth, is quenched below T-0D.  
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  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700242 Approved no  
  Call Number BT @ hernan @ Serial 221  
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Author Kaul, E.E.; Nieva, G. openurl 
  Title Oxygen doping effects on the magnetization of Bi2Sr2CaCu2O8+delta single crystalline system in the mixed state Type Journal Article
  Year 2000 Publication PHYSICA C Abbreviated Journal  
  Volume 341 Issue Pages 1343-1344  
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  Abstract We present a systematic study of the oxygen overdoping effects on the de magnetization loops of Bi2Sr2CaCu2O8+delta single crystalline samples. The overdoping is produced by high oxygen pressure (from 1 to 190 bar) annealing at 500 degreesC. The super conducting 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 far all the investigated oxygen contents. We show that the position of this second peak and the irreversibility field increase monotonically as a function of oxygen doping.  
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  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700271 Approved no  
  Call Number BT @ hernan @ Serial 222  
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Author Niebieskikwiat, D.; Civale, L.; Balseiro, C.A.; Nieva, G. openurl 
  Title Nonglassy relaxation by double kinks in YBa2Cu3O7-delta with columnar defects Type Journal Article
  Year 2000 Publication PHYSICAL REVIEW B Abbreviated Journal  
  Volume 61 Issue 10 Pages 7135-7141  
  Keywords  
  Abstract We present long-term relaxation measurements of the irreversible magnetization in YBa2Cu3O7-delta Single crystals with columnar defects. Within the single vortex pinning regime we find a nonglassy response at intermediate currents, in between the half loops and superkinks glassy regimes. We demonstrate that such behavior is due to double kink excitations whose critical nucleus has a size independent of current, and occur even in the presence of pinning energy dispersion.  
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  Series Volume Series Issue Edition  
  ISSN 1098-0121 ISBN Medium  
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  Notes ISI:000085985800092 Approved no  
  Call Number BT @ hernan @ Serial 229  
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Author André, M-O.; Polichetti, M.; Pastoriza, H.; Kes, P. H. doi  openurl
  Title Vortex dynamics in 2H-NbSe$_2$ containing a periodic channel structure Type Journal Article
  Year 2000 Publication Physica C Abbreviated Journal  
  Volume 338 Issue Pages 179-188  
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  Abstract We have measured the resistivity and magnetic AC susceptibility of 2H-NbSe single crystals containing alternating 2 stripes of irradiated and non-irradiated regions of columnar defects created by heavy-ion bombardment. Without applied magnetic field, the sample undergoes a double-step transition into the superconducting state, each step corresponding to the transitions in the irradiated and non-irradiated regions, respectively. For fields smaller than half of the matching field and upon increasing the temperature, the onset of flux motion in the non-irradiated channels occurs, when the applied stress due to the electrical current equals the shear stress at the channel edges, while depinning in the irradiated stripes occurs at higher temperature. The weak amplitude dependence of the shear process suggests that it takes place at the melting transition. We observed only a single-step transition at DC magnetic fields larger than half the matching field, because pinning by the columnar defects in the irradiated stripes is much less effective, and consequently the shear stress at the channel edges is strongly reduced. The comparison between the shear stress deduced from I curves and the theoretical value $?max = AC66$ yields a value for the constant Α, which is in good agreement with theoretical predictions.  
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  Call Number BT @ hernan @ andre99 Serial 2  
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Author Marconi, V. I.; Candia, S.; Balenzuela, P.; Pastoriza, H.; Domínguez, D.; Martinoli, P. url  doi
openurl 
  Title Orientational pinning and transverse voltage: Simulations and experiments in square Josephson junction arrays Type Journal Article
  Year 2000 Publication Phys. Rev. B Abbreviated Journal  
  Volume 62 Issue 6 Pages 4096-4104  
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  Abstract We study the dependence of the transport properties of square Josephson Junctions arrays with the direction of the applied dc current, both experimentally and numerically. We present computational simulations of current-voltage curves at finite temperatures for a single vortex in an array of $L\times L$ junctions ($Ha^2/?_0=f=1/L^2$), and experimental measurements in $100\times1000$ arrays under a low magnetic field corresponding to $f\approx0.02$. We find that the transverse voltage vanishes only in the directions of maximum symmetry of the square lattice: the [10] and [01] direction (parallel bias) and the [11] direction (diagonal bias). For orientations different than the symmetry directions, we find a finite transverse voltage which depends strongly on the angle φ of the current. We find that vortex motion is pinned in the [10] direction ($?=0$), meaning that the voltage response is insensitive to small changes in the orientation of the current near $?=0$. We call this phenomenon orientational pinning. This leads to a finite transverse critical current for a bias at $?=0$ and to a transverse voltage for a bias at $?\not=0$. On the other hand, for diagonal bias in the [11] direction the behavior is highly unstable against small variations of φ, leading to a rapid change from zero transverse voltage to a large transverse voltage within a few degrees. This last behavior is in good agreement with our measurements in arrays with a quasi-diagonal current drive.  
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  Call Number BT @ hernan @ marconi00 Serial 26  
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