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Author (up) Affolter, J.; Tesei, M.; Pastoriza, H.; Leemann, C.; Martinoli, P. doi  openurl
  Title Observation of Ising-like critical fluctuations in frustrated Josephson junction arrays with modulated coupling energies Type Journal Article
  Year 2002 Publication Physica C Abbreviated Journal  
  Volume 369 Issue Pages 313-316  
  Keywords  
  Abstract We report the results of ac sheet conductance measurements performed on fully frustrated square arrays of Josephson junctions whose coupling energy is periodically modulated in one of the principal lattice directions. Such systems are predicted to exhibit two distinct transitions: a low-temperature Ising-like transition triggered by the proliferation of domain walls and a high-temperature transition driven by the vortex unbinding mechanism of the Beresinskii-Kosterlitz-Thouless (BKT) theory. Both the superfluid and dissipative components of the conductance are found to exhibit features which unambiguously demonstrate the existence of a double transition whose properties are consistent with the Ising-BKT scenario.  
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  Notes Approved no  
  Call Number BT @ hernan @ affolter02 Serial 1  
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Author (up) Alejandro, G.; Steren, L. B.; Pastoriza, H.; Vega, D.; Granada, M.; Rojas Sánchez, J. C.; Sirena, M.; Alascio, B. url  doi
openurl 
  Title Magnetoresistance effect in (La, Sr)MnO_3 bicrystalline films Type Journal Article
  Year 2010 Publication Journal of Physics: Condensed Matter Abbreviated Journal  
  Volume 22 Issue 34 Pages 346007  
  Keywords  
  Abstract The angular dependence of the magnetoresistance effect has been measured on bicrystalline La 0.75 Sr 0.25 MnO 3 films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin–orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.  
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  Series Volume Series Issue Edition  
  ISSN 0953-8984 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ hernan @ Serial 596  
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Author (up) 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  
  Keywords  
  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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  Notes Approved no  
  Call Number BT @ hernan @ andre99 Serial 2  
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Author (up) Antonio, D.; Pastoriza, H. doi  openurl
  Title Nonlinear Dynamics of a Micromechanical Torsional Resonator: Analytical Model and Experiments Type Journal Article
  Year 2009 Publication Journal of Microelectromechanical Systems Abbreviated Journal J. Microelectromechanical Sys.  
  Volume 18 Issue 6 Pages 1396-1400  
  Keywords  
  Abstract Mechanical microoscillators have been valuable tools for magnetic measurements of microscopic samples. This paper presents an analytical model for the dynamics of an electrostatically actuated torsional oscillator and validates it experimentally. While, at low excitations, the system is well described by a damped linear oscillator, at higher oscillation amplitudes, a nonlinear regime is observed. Nonlinearity is originated exclusively by the electrostatic driving and detection and can be tuned by modifying the excitation or detection bias voltages. The parameters of the analytical model are obtained from the device dimensions and material properties. No empirical or fitting parameters are needed except for the quality factor, which is extracted from the linear resonance curve. The proposed model can be a valuable and straightforward tool for the design and analysis of many other similar devices based on electrostatically actuated mechanical resonators.  
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  Notes Approved no  
  Call Number BT @ hernan @ Serial 586  
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Author (up) Antonio, D.; Dolz, M.I.; Pastoriza, H. url  doi
openurl 
  Title Magnetization measurement of single La0.67Ca0.33MnO3 nanotubes in perpendicular magnetic fields using a micromechanical torsional oscillator Type Journal Article
  Year 2010 Publication Journal of Magnetism and Magnetic Materials Abbreviated Journal  
  Volume 322 Issue 5 Pages 488-493  
  Keywords Manganite nanotubes; Micromachined magnetometers; Shape anisotropy  
  Abstract Using a silicon micromechanical resonator as a sensitive magnetometer, the authors have studied both experimentally and theoretically the magnetic behavior of two isolated ferromagnetic nanotubes of perovskite La0.67Ca0.33MnO3. The article investigates the specific configuration where a magnetic field H is applied perpendicular to the magnetic easy axis of an isolated nanotube characterized by an uniaxial anisotropy constant K. In this situation, the magnetization M reduces the effective elastic constant kM of the resonator. This softening of the mechanical system is opposed to the hardening effect of M observed in a previous work, where H was applied parallel to the easy axis. Moreover, in this magnetic field configuration two distinct magnetization regimes are manifested, depending on the magnitude of H. For H[not double greater-than sign]2K/M the magnetization is almost parallel to the applied magnetic field and for H[double less-than sign]2K/M it is almost parallel to the easy axis of the nanotube. At a certain value of H there is a sharp transition  
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  Series Volume Series Issue Edition  
  ISSN 0304-8853 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ hernan @ 13272 Serial 585  
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Author (up) Antonio, D.; Dolz, M.I.; Pastoriza, H. url  openurl
  Title Micromechanical magnetometer using an all-silicon nonlinear torsional resonator Type Journal Article
  Year 2009 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.  
  Volume 95 Issue 13 Pages 133505-3  
  Keywords damping; eddy currents; elemental semiconductors; magnetometers; micromechanical devices; nonlinear dynamical systems; oscillations; Q-factor; resonators; silicon  
  Abstract In this work, a micromagnetometer employing a nonlinear torsional resonator with a high quality factor Q is presented experimentally. Oscillatory rotation of a conducting plate in the sensed magnetic field H induces eddy currents that dissipate energy. Due to the nonlinear response of the oscillator, the resulting mechanical damping originates frequency shifts in the resonance curve that depend on H. Nonlinearity results from the electrostatic detection, which introduces high order electrical spring constants. The device is fabricated with a standard silicon process and does not incorporate ferromagnetic materials. An analytical nonlinear model that correctly describes the device is also introduced.  
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  Publisher AIP Place of Publication Editor  
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  Notes Approved no  
  Call Number BT @ hernan @ Serial 564  
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Author (up) Antonio, D.; Julian, P.; Mandolesi, P.; Pastoriza, H. openurl 
  Title Amplificador de transimpedancia criogénico para detección capacitiva de MEMS Type Conference Article
  Year 2007 Publication Actas de la Escuela Argentina de Microelectrónica, Tecnología y Aplicaciones: Trabajos Breves Abbreviated Journal  
  Volume 1 Issue 1 Pages 49-51  
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  Notes Brief Paper Approved no  
  Call Number BT @ hernan @ antonio07 Serial 3  
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Author (up) Bolecek, N.R.C.; Dolz, M.I.; Pastoriza, H.; Konczykowski, M.; van der Beek, C.J.; Kolton, A.B.; Fasano, Y. url  doi
openurl 
  Title Excess of topological defects induced by confinement in vortex nanocrystals Type Journal Article
  Year 2017 Publication Physical Review B Abbreviated Journal PRB  
  Volume 96 Issue 2 Pages 024507  
  Keywords  
  Abstract We directly image individual vortex positions in nanocrystals in order to unveil the structural property that contributes to the depletion of the entropy jump entailed at the first-order transition. On reducing the nanocrystal size, the density of topological defects increases near the edges over a characteristic length. Within this “healing-length” distance from the sample edge, vortex rows tend to bend, while towards the center of the sample, the positional order of the vortex structure is what is expected for the Bragg-glass phase. This suggests that the healing length may be a key quantity to model confinement effects in the first-order transition of extremely layered vortex nanocrystals.  
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  Publisher American Physical Society Place of Publication Editor  
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  Notes Approved no  
  Call Number BT @ hernan @ 10.1103/PhysRevB.96.024507 Serial 762  
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Author (up) Cejas Bolecek, N.R.; Kolton, A.B.; Konczykowski, M.; Pastoriza, H.; Dominguez, D.; Fasano, Y. url  doi
openurl 
  Title Vortex matter freezing in Bi2Sr2CaCu28 samples with a very dense distribution of columnar defects Type Journal Article
  Year 2016 Publication Physical Review B Abbreviated Journal Phys. Rev. B  
  Volume 93 Issue 5 Pages 054505  
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  Abstract We show that the dynamical freezing of vortex structures nucleated at diluted densities in Bi2Sr2CaCu2O8 samples with a dense distribution of columnar defects, B∼10−2BΦ with BΦ=5kG, results in configurations with liquidlike correlations. We propose a freezing model considering a relaxation dynamics dominated by double-kink excitations driven by the local stresses obtained directly from experimental images. With this model we estimate the relaxation barrier and the freezing temperature. We argue that the low-field frozen vortex structures nucleated in a dense distribution of columnar defects thus correspond to an out-of-equilibrium nonentangled liquid with strongly reduced mobility rather than to a snapshot of a metastable state with divergent activation barriers as, for instance, expected for the Bose-glass phase at equilibrium.  
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  Publisher American Physical Society Place of Publication Editor  
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  Notes Approved no  
  Call Number BT @ pedrazp @ 10.1103/PhysRevB.93.054505 Serial 738  
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Author (up) Cejas Bolecek, N.R.; Dolz, M.I.; Kolton, A.; Pastoriza, H.; Beek, C.Jvander; Konczykowski, M.; Menghini, M.; Nieva, G.; Fasano, Y. doi  openurl
  Title Geometrical Confinement Effects in Layered Mesoscopic Vortex Matter Type Journal Article
  Year 2015 Publication Journal of Low Temperature Physics Abbreviated Journal J. Low Temp. Phys.  
  Volume 179 Issue 1-2 Pages 35-41  
  Keywords Vortex matter; Mesoscopic physics; Layered superconductors  
  Abstract We study the geometrical confinement effect in Bi 2 Sr 2 CaCu 2 O 8+δ mesoscopic vortex matter with edge-to-surface ratio of 7–12 %. Samples have in-plane square and circular edges, 30 μ m widths, and ∼ 2 μ m thickness. Direct vortex imaging reveals the compact planes of the structure align with the sample edge by introducing topological defects. The defect density is larger for circular than for square edges. Molecular dynamics simulations suggest that this density is not an out-of-equilibrium property but rather determined by the geometrical confinement.  
  Address  
  Corporate Author Thesis  
  Publisher Springer US Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0022-2291 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 711  
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