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Author |
Fasano, Y.; Menghini, M.; de la Cruz, F.; Nieva, G. |
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Title  |
Weak interaction and matching conditions for replicas of vortex lattices |
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Year |
2000 |
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PHYSICAL REVIEW B |
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62 |
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22 |
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15183-15189 |
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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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0163-1829 |
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ISI:000165883800075 |
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BT @ hernan @ |
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219 |
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Author |
André, M-O.; Polichetti, M.; Pastoriza, H.; Kes, P. H. |
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Title |
Vortex dynamics in 2H-NbSe$_2$ containing a periodic channel structure |
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Journal Article |
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Year |
2000 |
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Physica C |
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338 |
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179-188 |
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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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BT @ hernan @ andre99 |
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2 |
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Silhanek, K.; Guimpel, J.; Civale, L.; Lanza, H.; Levy, P. |
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Title |
Thickness effects on the pinning by columnar defects |
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Journal Article |
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Year |
2000 |
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PHYSICA C |
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341 |
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1217-1218 |
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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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0921-4534 |
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ISI:000165855700208 |
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BT @ hernan @ |
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175 |
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Author |
Sirena, M.; Steren, L.; Guimpel, J. |
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Title |
Thickness dependence of the properties of La0.6Sr0.4MnO3 thin films |
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Journal Article |
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Year |
2000 |
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Thin Solid Films |
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373 |
Issue |
1-2 |
Pages |
102-106 |
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We have studied the thickness dependence of the transport and magnetic properties of strongly textured La0.6Sr0.4MnO3 thin films grown on MgO and SrTiO3, for thickness between 5 and 500 nm. While the resistivity and the magnetoresistance are strongly affected, the magnetization is only moderately changed. The effect on the metal-insulator transition, the low field magnetoresistance and carrier localization is dependent on the substrate, evidencing the effect of the induced defects and strains. (C) 2000 Elsevier Science S.A. All rights reserved. |
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0040-6090 |
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ISI:000090045900024 |
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BT @ hernan @ |
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176 |
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Steren, L.B.; Sirena, M.; Guimpel, J. |
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Title |
Substrate influence on the magnetoresistance and magnetic order in La0.6Sr0.4MnO3 films |
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Journal Article |
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Year |
2000 |
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JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS |
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211 |
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1-3 |
Pages |
28-34 |
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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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0304-8853 |
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ISI:000085772100006 |
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BT @ hernan @ |
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179 |
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Steren, L.B.; Sirena, M.; Guimpel, J. |
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Title |
Substrate effect on the magnetic behavior of manganite films |
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Journal Article |
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Year |
2000 |
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JOURNAL OF APPLIED PHYSICS |
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87 |
Issue |
9 |
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6755-6757 |
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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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0021-8979 |
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ISI:000086728800281 |
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BT @ hernan @ |
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178 |
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Author |
Luzuriaga, J. |
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Title |
Sphere on a vibrating reed for measurements of turbulence in superfluid helium |
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Journal Article |
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Year |
2000 |
Publication |
Journal of Alloys and Compounds |
Abbreviated Journal |
J Alloys Compd |
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265-268 |
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Cantilever beams; Computational methods; Laminar flow; Oscillators (electronic); Phase transitions; Turbulent flow; Vibrations (mechanical); Oscillating spheres; Spherical geometries; Vibrating reeds; Superfluid helium |
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A modification of the vibrating reed, in which a massive sphere is made to oscillate at the end of a cantilevered beam, has been used for measurements in superfluid helium. The apparatus operates in the same way as a conventional vibrating reed with capacitive detection and drive. However, when operating submerged in the liquid, the frequency changes give information on the superfluid fraction, and the dissipation can be used to obtain information on the change of liquid flow, from laminar to turbulent. The spherical geometry allows an exact calculation of all parameters in the laminar regime, so departures due to the turbulence can be better quantified. The method has been found to work well in practice, and some measurements on the turbulent regime in the superfluid are presented. |
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Centro At |
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Elsevier Sequoia SA |
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Buenos Aires, Argent |
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12th International Conference on Internal Friction and Ultrasonic Attenuation in Solids (ICIFUAS-12) |
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Series Volume |
310 |
Series Issue |
1-2 |
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09258388 (ISSN) |
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Conference code: 57483; Export Date: 28 April 2009; Source: Scopus; CODEN: JALCE; doi: 10.1016/S0925-8388(00)00962-2; Language of Original Document: English; Correspondence Address: Luzuriaga, Javier; Centro Atomico Bariloche Bariloche, Argentina; Sponsors: ABDUS SALAM International Centre for Theoretical Physics; Centre for Industrial Research (CINI); Comision Nacional de Actividades Espaciales (CONAE) |
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478 |
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Herbsommer, J.A.; Nieva, G.; Luzuriaga, J. |
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Title |
Reproducibility of the disordered vortex structure in twinned single crystals of YBCO |
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Journal Article |
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2000 |
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Physica C |
Abbreviated Journal |
Physica C |
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341 |
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1087-1088 |
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Bitter decorations of the vortices in twinned single crystal YBCO have been obtained to study the disordered structure formed on successive cooldowns of the sample under the same conditions of field and temperature. Between succesive decorations, the iron dots could be removed completely, giving a surface clean enough for further decoration. It was found that successive realizations of the disordered vortex state were very similar at long range, and differed mostly on short scales, compared to the average vortex separation. We have quantified the correlation between successive structures, and double sided decorations have been also performed to compare with the extent of spatial correlation in the applied field direction. The coincidence of the position of the vortices in successive realizations of the structure, is unexpected, and indicates an unusual behavior for a glassy system. Our technique makes it possible to image the position of the vortices in detail and repeatedly, providing us with a model amorphous system in which to study the reproducibility of the disordered structure. |
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0921-4534 |
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ISI:000165855700143 |
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BT @ hernan @ |
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220 |
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Herbsommer, J.A.; Nieva, G.; Luzuriaga, J. |
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Title |
Repetition of the disordered pattern in successive solidifications of vortex matter observed by Bitter decoration |
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Journal Article |
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Year |
2000 |
Publication |
Physical Review B |
Abbreviated Journal |
Phys. Rev. B |
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Volume |
62 |
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1 |
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678-681 |
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Repeated images of the vortex structure in YBa2Cu3O7-delta Single crystals have been obtained, using the Bitter technique. By removing the iron dots between each decoration experiment, it is possible to image the vortices in different cooldown runs done under the same field and temperature conditions. The images show that these different realizations of a disordered vortex state found in twinned crystals are very similar at long range and differ only in small-scale detail. This is unusual behavior in glassy systems, where expectations are that successive configurations will differ over many scales. In contrast, ordered vortex crystals in clean samples can form with different orientations in different runs, therefore differing at long ranges. Double-sided decorations have been performed in twinned samples, and the correlation between images in both sides of the sample is similar in magnitude but slightly different qualitatively than that found in successive decorations. |
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0163-1829 |
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ISI:000088037000106 |
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BT @ hernan @ |
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225 |
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Author |
Kaul, E.E.; Nieva, G. |
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Title |
Oxygen doping effects on the magnetization of Bi2Sr2CaCu2O8+delta single crystalline system in the mixed state |
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Journal Article |
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Year |
2000 |
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PHYSICA C |
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341 |
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1343-1344 |
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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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0921-4534 |
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ISI:000165855700271 |
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BT @ hernan @ |
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222 |
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