Allard, D., I. Allekotte, C. Alvarez, H. Asorey, H. Barros, X. Bertou, O. Burgoa, M. G. Berisso, O. Martinez, P. M. Loza et al. "Use of water-Cherenkov detectors to detect Gamma Ray Bursts at the Large Aperture GRB Observatory (LAGO)." NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 595, no. 1 (2008): 70–72.
Abstract: The Large Aperture GRB Observatory (LAGO) project aims at the detection of high energy photons from Gamma Ray Bursts (GRB) using the single particle technique in ground-based water-Cherenkov detectors (WCD). To reach a reasonable sensitivity, high altitude mountain sites have been selected in Mexico (Sierra Negra, 4550 m a.s.l.), Bolivia (Chacaltaya, 5300 m a.s.l.) and Venezuela (Merida, 4765 m a.s.l.). We report on detector calibration and operation at high altitude, search for bursts in 4 months of preliminary data, as well as search for signal at ground level when satellites report a burst. (C) 2008 Elsevier B.V. All rights reserved.
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Braghta, A., G. Schmerber, A. Derory, J. G. Sereni, and J. P. Kappler. "Magnetic and thermal properties of Ce2Pd2Sn." Journal of Magnetism and Magnetic Materials 320, no. 6 (2008): 1141–1145.
Abstract: X-ray diffraction, susceptibility and specific heat studies on ternary Ce2Pd2Sn intermetallic compound and on its isostructural nonmagnetic compound La2Pd2Sn are reported. On Ce2Pd2Sn in absence of magnetic field, we confirm the existence of two magnetic transitions at T-N = 4.8K (antiferromagnetic transition) and T-C = 2.2K (ferromagnetic transition) and the specific heat results, measured down to 0.5 K, allow to recognize the transition at 2.2K as a first-order transition. A description based on molecular field calculations for the S = 1/2 resonant level model leads to a characteristic Kondo T-K of about 3K. (C) 2007 Elsevier B.V. All rights reserved.
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Bridoux, G., G. Nieva, and F. de la Cruz. "Phase-coherence effects in vortex transport entropy." PHYSICAL REVIEW LETTERS 101, no. 11 (2008): 117002.
Abstract: Nernst and electrical resistivity measurements in superconducting YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta with and without columnar defects show a distinctive thermodynamics of the respective liquid vortex matter. At a field-dependent high temperature region in the H-T phase diagram, the Nernst signal is independent of structural defects in both materials. At lower temperatures, in YBa2Cu3O7-delta, defects contribute only to the vortex mobility, and the transport entropy is that of a system of vortex lines. The transition to lower temperatures in Bi2Sr2CaCu2O8+delta has a different origin; the maximum in the Nernst signal when decreasing temperature is not associated with transport properties but with the entropy behavior of pancake vortices in the presence of structural defects.
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D. Antonio, H. Pastoriza, P. Julian, P. Mandolesi. "Cryogenic transimpedance amplifier for micromechanical capacitive sensors." Review of Scientific Instruments 79, no. 8 (2008): 084703.
Abstract: We developed a cryogenic transimpedance amplifier that works at a broad range of temperatures, from room temperature down to 4 K. The device was realized with a standard complementary metal oxide semiconductor 1.5 μm process. Measurements of current-voltage characteristics, open-loop gain, input referred noise current, and power consumption are presented as a function of temperature. The transimpedance amplifier has been successfully applied to sense the motion of a polysilicon micromechanical oscillator at low temperatures. The whole device is intended to serve as a magnetometer for microscopic superconducting samples
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Dolz, M. I., W. Bast, D. Antonio, H. Pastoriza, R. D. J. Sánchez Curiale, and A. G. Leyva. "Magnetic Behavior of Single La0.67Ca0.33MnO$_3$ Nanotubes: Surface and Shape Effects." J. Appl. Phys. 103 (2008): 083909.
Abstract: We report magnetization experiments in two magnetically isolated ferromagnetic nanotubes of perovskite Lai0.67Ca0.33MnO$_3$. The results show that the magnetic anisotropy is determined by the sample shape, although the coercive field is reduced by incoherent magnetization reversal modes. The temperature dependence of the magnetization reveals that the magnetic behavior is dominated by grain surface properties. These measurements were acquired using a silicon micromechanical oscillator working in its resonant mode. The sensitivity was enough to measure the magnetic properties of these two samples with a mass lower than 14 pg and to obtain for the first time the magnetization loop for one isolated nanotube.
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El-Khatib, S., A. M. Alsmadi, V. Correa, A. V. Andreev, A. Lacerda, F. Nasreen, and H. Nakotte. "Electronic properties of single crystalline UNi[sub 0.39]Rh[sub 0.61]Al." Journal of Applied Physics 103, no. 7 (2008): 07B714–3.
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Hartmann, S., M. Deppe, N. Oeschler, N. Caroca-Canales, J. G. Sereni, and C. Geibel. "Ferromagnetism in CePd1-xRhx single crystals." Journal of Optoelectronics and Advanced Materials 10, no. 7 (2008): 1607–1611.
Abstract: The orthorhombic CePd1-xRhx alloy exhibits a continuous evolution from a ferromagnetic ground state at x = 0 to
intermediate-valence behavior for x = 1. Here, we report on specific heat CP(T), resistivity Ï(T) and magnetization M(T)
measurements on single crystals in a Rh concentration range 0.2 < x < 0.65 exploring the ferromagnetic side of the
magnetic phase diagram. The transport and thermodynamic properties of the ferromagnetic phase have been investigated
in the temperature range from 300 K down to 0.35 K and analyzed in terms of a gap in the magnon spectrum and an
underlying Kondo contribution. Crystal electric field parameters are deduced from specific heat measurements well above
Tc- The competition between Kondo effect and ferromagnetism has been studied in dependence of the Rh concentration in
the system. Particularly, the enhanced Sommerfeld coefficient γ(x) indicates strong Kondo interactions when the Curie
temperature is reduced.
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Lora-Serrano, R., V. F. Correa, C. Adriano, C. Giles, J. G. S. Duque, E. Granado, P. G. Pagliuso, T. P. Murphy, E. C. Palm, S. W. Tozer et al. "First order magnetic transition and magnetoelastic effects in Sm2IrIn8." Physica B 403, no. 5-9 (2008): 1365–1367.
Abstract: We report measurements of temperature dependent heat capacity, thermal expansion and high resolution X-ray diffraction (XRD) taken on single crystals of Sm2IrIn8 intermetallic compound. This compound belongs to the RmMnIn3m+2n family (R=rare earth, m=1, 2, n=0, 1 and M=Rh, Ir and Co) which includes a number of heavy fermion superconductors for R=Ce. Particularly, Sm2IrIn8 is the only member of this family to present a first order magnetic phase transition (FOMT). Both thermal expansion and heat capacity data show very pronounced sharps peaks at View the MathML source consistent with an FOMT. The linear thermal-expansion coefficient is anisotropic and both c-axis and basal ab plane coefficients change discontinuously at 14.2 K. This change is negative for both direction in contrast to what was found for other members of family such as Ce2RhIn8 and CeRhIn5. The zero-field high resolution XRD data at 14.2 K shows no evidence for a tetragonal-to-orthorhombic structural phase transition. We discuss our results considering tetragonal crystalline field effects (CEF), quadupolar interactions, antiferromagnetic domains and magnetoelastic effects.
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Lovey, F. C., A. M. Condo, J. Guimpel, and M. J. Yacaman. "Shape memory effect in thin films of a Cu-Al-Ni alloy." MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481 (2008): 426–430.
Abstract: Thin films of Cu-26.9 at.% Al-5.5 at.% Ni were grown by dc magnetron sputtering from the alloy target previously melted in an induction furnace. The films were grown either on glass or (100)Si substrates at room temperature. The films, of approximately 3 μm thickness, were peeled off from the substrate for further studies. The structures and microstructures of the as grown films were analysed by transmission electron microscopy. A nanometric mixture of BCC and 2H phases was found irrespective of the substrate. The shape memory effect was not observed for this structural state. After an annealing at 1023 K for 3600s in He or Ar flux, followed by quenching to room temperature, the films were found to be in a martensitic state. Mainly the 18R structure was observed. At this stage the films were mechanically deformed at room temperature and then heated up to 373 K. A good shape recovery was observed to take place in a temperature range between 334 and 360 K. (C) 2007 Elsevier B.V. All rights reserved.
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Monton, C., F. de la Cruz, and J. Guimpel. "Magnetic state modification induced by superconducting response in ferromagnet/superconductor Nb/Co superlattices." PHYSICAL REVIEW B 77, no. 10 (2008).
Abstract: Magnetization measurements in superconductor/ferromagnet Nb/Co superlattices show a complex behavior as a function of temperature, applied field, and sample history. Based on a simple model, it is shown that this behavior is due to an interplay between the superconductor magnetization temperature dependence, the ferromagnet magnetization time dependence, and the stray fields of both materials. It is also shown that the magnetic state of the Co layers is modified by the Nb superconducting response, implying that the problem of a superconductor/ferromagnetic heterogeneous sample has to be solved in a self-consistent manner.
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Monton, C., C. A. Ramos, J. Guimpel, and R. D. Zysler. "Experimental evidence of magnetic anisotropy induction by superconductivity in superlattices." Applied Physics Letters 92, no. 15 (2008).
Abstract: We present a study of Nb/Co superlattices by ferromagnetic resonance. We find that when the superconductor enters the Meissner state, an anisotropy field around 400 Oe, parallel to the applied field, appears in the ferromagnetic layers, consistent with the superconducting flux expelled from the superconducting layers. This anisotropy field is an important key to understand previous results showing that the superconductor layers modify the magnetic state of the ferromagnetic layers. (c) 2008 American Institute of Physics.
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R. Nath, A. A. Tsirlin, E. E. Kaul, M. Baentiz, N. Buettgen, H. Rosner y C. Geibel. "Strong frustration due to competing ferro- and antiferromagnetic interactions: magnetic properties of M(VO)2(PO4)2 (M = Ca and Sr)." Physical Review B – Condensed Matter and Materials Physics 78 (2008): 024418.
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Sereni, J. G., M. Gomez Berisso, A. Braghta, G. Schmerber, and J. P. Kappler. "Unstable Shastry-Sutherland phase in Ce2Pd2Sn." Physical Review B – Condensed Matter and Materials Physics 80, no. 2 (2008): 022428.
Abstract: Thermal (CP) , magnetic ( M and χac ), and transport (Ï) measurements on Ce2Pd2Sn are reported. High-temperature properties are well described by the presence of two excited crystal-field levels at (65±5)K and (230±20)K , with negligible hybridization (Kondo) effects. According to literature, two transitions were observed at TM=4.8K and TC=2.1K , respectively. The upper transition cannot be considered as a standard antiferromagnetic because of frustration effects in a triangular network of Ce atoms and the positive sign of the paramagnetic temperature θPLT=4.4K . The nature of the intermediated phase is described accounting for the formation of ferromagnetic (F) Ce dimers disposed in a quasi-two-dimensional square lattice, resembling a Shastry-Sutherland pattern. According to hysteretic features in Ï(T) and χac(T) , the lower F transition is of first order, with CP(T<TC) revealing a gap of anisotropy Eg≈7K .
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Sereni, J. G., T. Radu, and A. Pikul. "Analysis of the very low temperature phase diagrams of two Ce compounds." Journal of Optoelectronics and Advanced Materials 10, no. 7 (2008): 1645–1650.
Abstract: A rich variety of behaviours have been found studying the physical properties of Ce-lattice systems tuned around their critical regions, particularly in the few phase boundaries traced along more than a decade of temperature. The phase diagram of two Ce-systems: the antiferromagnetic CeIn3-xSnx and ferromagnetic CePd1-xRhx are analyzed covering the 10K > T > 0.02K range of temperature. Their respective magnetic phase diagrams are described as an interplay between different components determined after analyzing their thermodynamic properties. In the former compound, signs for the formation of a new phase are observed at very low temperature, whereas in the latter a field induced contribution is detected behind the critical point.
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Zapf, V. S., V. F. Correa, P. Sengupta, C. D. Batista, M. Tsukamoto, N. Kawashima, P. Egan, C. Pantea, A. Migliori, J. B. Betts et al. "Direct measurement of spin correlations using magnetostriction." Physical Review B (Condensed Matter and Materials Physics) 77, no. 2 (2008): 020404.
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Zarate, J. J., and H. Pastoriza. "Correction algorithm for the proximity effect in e-beam lithography." In Micro-Nanoelectronics, Technology and Applications, 2008. EAMTA 2008. Argentine School of, 38–42., 2008.
Abstract: e-beam lithography is a technique capable of fabricate sub-micrometer planar structures. The ultimate resolution in this technique is limited mainly by the proximity effect where the dose accumulated in one spacial point is affected by the irradiated dose in its neighborhood. The relevance of this effect in one particular pattern strongly depends on its geometry, the sensitivity of the resist and the physical characteristics of the substrate. In this work we present a numerical algorithm to calculate the nominal dose needed to be applied in each point of the geometry that results in an optimal net dose for an efficient pattern transfer.
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