Alejandro, G., L. B. Steren, H. Pastoriza, D. Vega, M. Granada, J. C. Rojas Sánchez, M. Sirena, and B. Alascio. "Magnetoresistance effect in (La, Sr)MnO_3 bicrystalline films." Journal of Physics: Condensed Matter 22, no. 34 (2010): 346007.
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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Antonio, D., M. I. Dolz, and H. Pastoriza. "Magnetization measurement of single La0.67Ca0.33MnO3 nanotubes in perpendicular magnetic fields using a micromechanical torsional oscillator." Journal of Magnetism and Magnetic Materials 322, no. 5 (2010): 488–493.
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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Conte, V., J. L. Giordano, J. J. Zarate, and J. Luzuriaga. "Superconducting Devices for Radioastronomy; First Steps in Chile: SNS-junction Fabrication.", 424–427. Vol. 1., 2010.
Abstract: We present results of the microfabrication of Josephson Junctions (JJs) of Superconductor-Normal-superconductor (SNS) type, as a first step in the acquisition of the know-how of superconducting devices applied to radioastronomy. A twojunction SQUID was built using a Nb/Al bilayer deposited on a Si wafer. The procedure needs only one mask and a single UV exposure (i.e., one photolithography step). We show the micrograph and the observed non linear characteristic I-V curve at 4K of the first device fabricated in the framework of ALMA Grant 31090010.
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Deppe, M., N. Caroca-Canales, J. G. Sereni, and C. Geibel. "Evidence for a metamagnetic transition in the heavy Fermion system CeTiGe." In Journal of Physics: Conference Series, 012026. Vol. 200. International Conference on Magnetism, ICM 2009 200, no. SECTION 1. Karlsruhe, 2010.
Abstract: A recent study of CeTiGe identified this compound as a paramagnetic heavy Fermion system where the full J = 5/2 multiplet is involved in the formation of the ground state. Here we present a preliminary investigation of the dc-magnetization Mdc(H) and of the magnetoresistance Ï(H) of polycrystalline CeTiGe samples in applied magnetic fields up to μ0H = 14 T. The results reveal a pronounced metamagnetic transition at a critical field μ0Hc ≈ 13.5 T at low temperatures, with a step like increase in Mdc(H) of at least 0.6 μB/Ce. The metamagnetic transition leads to a strong decrease in Ï(H). A clear hysteresis in Mdc(H) and Ï(H) indicate that in CeTiGe these metamagnetic features correspond to a true thermodynamic, first order type transition in contrast to the critical behavior observed in the canonical system CeRu2Si2. Measurements at higher temperatures showed a continuous suppression of the metamagnetic transition with increasing T, which vanishes at T ∼ 30 K. © 2010 IOP Publishing Ltd.
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Dolz, M. I., A. B. Kolton, and H. Pastoriza. "Direct determination of the collective pinning radius in the cuprate superconductor Bi2 Sr2 CaCu2 O8+ delta." Physical Review B 81, no. 9 (2010): 092502.
Abstract: We study the onset of the irreversible magnetic behavior of vortex matter in micron-sized Bi2Sr2CaCu2O8+δ single crystals by using silicon micro-oscillators. We find an irreversibility line appearing well below the thermodynamic Bragg-glass melting line at a magnetic field which increases both with increasing the sample radius and with decreasing the temperature, paradoxically implying the existence of a reversible vortex solid. We show that at this irreversibility line, the sample radius can be identified with the crossover length between the Larkin and the random-manifold regimes of the vortex-lattice transverse roughness. Our method thus allows to determine, as a function of temperature and applied magnetic field, the minimum size of a vortex system that can be collectively pinned, or the so-called three-dimensional weak collective pinning Larkin radius, in a direct way.
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Fasano, Y., I. Maggio-Aprile, N. D. Zhigadlo, S. Katrych, J. Karpinski, and Ã. ˜. Fischer. "Local quasiparticle density of states of superconducting SmFeAsO1 − xFx single crystals: Evidence for spin-mediated pairing." Physical Review Letters 105 (2010): 167005–167008.
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Gil, D. M., M. C. Navarro, M. C. Lagarrigue, J. Guimpel, R. E. Carbonio, and M. I. Gómez. "Synthesis and structural characterization of perovskite YFeO3 by thermal decomposition of a cyano complex precursor, Y[Fe(CN)6]·4H2O}." Journal of Thermal Analysis and Calorimetry (2010): 1–8.
Abstract: The thermal decomposition of Y[Fe(CN)6]·4H2O has been studied in order to investigate the formation of the multi-ferroic oxide YFeO3. The starting material (Y[Fe(CN)6]·4H2O) and the decomposition products were characterized by IR spectroscopy, thermal analysis, X-ray powder diffraction (PXRD), and scanning electron microscopy. Metastable YFeO3 with hexagonal structure, space group P63/mmc, was obtained by thermal decomposition of Y[Fe(CN)6]·4H2O at 600 °C in air. Orthorhombic YFeO3 was obtained by the same method at T ≥ 800 °C in air. The crystal structure of orthorhombic YFeO3 was refined by Rietveld analysis using PXRD data. We found that it was slightly deficient in Y3+, which is in agreement with the small amount of Y2O3 found as impurity in the sample. The formula of the orthorhombic phase is Y0.986FeO3
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Haberkorn, N., F. C. Lovey, A. M. Condó, and J. Guimpel. "Development and characterization of shape memory Cu-Zn-Al thin films." Materials Science and Engineering B: Solid-State Materials for Advanced Technology 170, no. 1-3 (2010): 5–8.
Abstract: Ternary Cu-Zn-Al alloys show good shape memory properties with narrow hysteresis and a wide range of martensitic transformation temperature (Ms), depending on the alloy composition. Thin films of Cu-Zn-Al with shape memory effect were grown for the first time using a new procedure. First Cu-Al thin films were obtained by DC sputtering on Si (1 0 0) substrates at room temperature, and second, the Cu-Al films were encapsulated and annealed in the presence of a Cu-Zn-Al bulk reference in order to fix a Zn vapour pressure. In this way a controlled amount of Zn is transported from the bulk reference into the film, in such a way that the Ms of the film becomes nearly the same as the bulk reference. The structures and microstructures of the as grown films were analysed by X-ray diffraction and transmission electron microscopy. The martensitic transformation temperature was determined by resistivity measurements.
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Luzuriaga, J. "Mean free path in soccer and gases." European Journal of Physics 31, no. 5 (2010): 1071–1076.
Abstract: The trajectories of the molecules in an ideal gas and of the ball in a soccer game are compared. The great difference between these motions and some similarities are discussed. This example could be suitable for discussing many concepts in kinetic theory in a way that can be pictured by students for getting a more intuitive understanding. It could be suitable for an introductory course in vacuum techniques or undergraduate courses in kinetic theory of gases. Without going into the slightly harder quantitative results, the analysis presented might be used for introducing some ideas of kinetic theory qualitatively to high school students. © 2010 IOP Publishing Ltd.
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M. Sirena, A. Zimmers, N. Haberkorn, E. E. Kaul, L. B. Steren, J. Lesueur, T. Wolf, Y. Le Gall, J.-J. Grob y G. Faini. "nfluence of ion implantation on the magnetic and transport properties of manganite Films." Physical Review B (Condensed Matter and Materials Physics) 81 (2010): 134439.
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Niebieskikwiat, D., N. Haberkorn, R. Guitarra, and J. Guimpel. "Magnetic properties of SrTiO3/Pr2/3Ca 1/3MnO3 multilayers." In Journal of Physics: Conference Series, 072069. Vol. 200., 2010.
Abstract: Nanoscale ferromagnetic (FM) clusters embedded within insulating (I) layers of the antiferromagnetic Pr2/3Ca1/3MnO3 (PCMO) are known to improve the magnetoresistance ratio of FM-I magnetoresistive multilayers. Here, we study the magnetic properties of perovskite superlattices comprised of five PCMO layers of variable thickness t separated by 5nm-thick spacers of SrTiO3 (STO). Several multilayers (1.5 nm ≤ t ≤ 8 nm) were grown on (001) STO substrates by magnetron sputtering. We show that the magnetic moment of PCMO due to the FM inclusions presents a maximum for t ∼ 3 nm, accompanied by an abrupt increase of coercivity and exchange bias field. The nonmagnetic nature of the neighboring STO layers demonstrates that the observed behavior is not related to any interlayer exchange coupling, but the geometrical matching between layer thickness and FM domain size is the key driver for the enhancement of the FM moment and anisotropy energy. These results open a new door for the optimization of perovskite based spintronic devices.
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Piriou, A., E. Giannini, Y. Fasano, C. Senatore, and O. Fischer. "Vortex phase diagram and temperature-dependent second-peak effect in overdoped Bi2Sr2CuO6+d crystals." Physical Review B 81 (2010): 144517–144524.
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Sarkar, R., M. Baenitz, J. G. Sereni, and C. Geibel. "29Si NMR study of the heavy fermion system CeRuSi." Journal of Physics: Conference Series 200 (2010): 012173.
Abstract: A recent investigation of the low temperature properties of the paramagnetic heavy fermion system CeRuSi revealed an anomalous decrease of the coefficient C/T below 6 K, indicating a second low energy scale well below the Kondo temperature of about 50 K. We started an investigation of this unusual behavior using the local probe 29Si-NMR. Here a preliminary 29Si field sweep NMR study in the temperature 4.2-200 K is reported. 29Si-NMR powder spectra obtained at 72.9 MHz could be simulated and shift components 29Kab(T) and 29K c(T) were determined. The shift along the basal plane 29Kab(T) shows the expected behavior with a Curie-Weiss dependence at high T merging in a constant value below 15 K. In contrast the shift along the tetragonal axis reveals an anomalous T dependence below 15 K where 29Kc(T) drops by a factor of 2, confirming the presence of a further low T energy scale. We suspect this drop to be related to the anomalous decrease of C/T below 6 K and discuss possible mechanism. © 2010 IOP Publishing Ltd.
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Sereni, J. G., N. Caroca-Canales, M. Kumar, N. Oeschler, M. Gómez Berisso, and C. Geibel. "CeRuGe and CeRuSi: Heavy fermion systems with some unusual features." Journal of Physics: Conference Series 200, no. 1 (2010): 012181.
Abstract: We have investigated the physical properties of CeRuSi, its homologue CeRuGe and some doped La alloys. All of them present similar properties: large paramagnetic temperatures θp ##IMG## [http://ej.iop.org/icons/Entities/approx.gif] {approx} −100 K and the level off of χ( T ) below ##IMG## [http://ej.iop.org/icons/Entities/approx.gif] {approx} 10 K in coincidence with the maximum decrease of p ( T ), which starts to drop below 25 K. The respective γ ( CeRuSi ) ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 0.18 and γ ( CeRuGe ) ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 0.15 J/molK 2 coefficients reveal a heavy fermion character, with a Kondo temperature T K ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 50 K comparable to the crystal field splitting. In both compounds a broad maximum in C P ( T )/ T is observed around 5 K, whose origin is yet not clear. In contrast to the usual behavior observed in Kondo lattice systems, when Si is replaced by Ge T K ##IMG## [http://ej.iop.org/icons/Entities/propto.gif] {propto} θ p and 1/γ practically does not decreases despite the unit cell volume of CeRuGe is about 3% larger than that of CeRuSi. We discuss possible origins for these unusual features.
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Sereni, J. G., M. Gomez Berisso, N. C. Canales, M. Deppe, and C. Geibel. "Tuning ground state degeneracy and quantum criticality in Ce1-xLaxTiGe." Physica Status Solidi (B) Basic Research 247, no. 3 (2010): 707–709.
Abstract: We have tuned the paramagnetic heavy Fermion (HF) system CeTiGe to a more magnetic state and toward quantum criticality (QC) by partially substituting La for Ce. The induced volume expansion leads to a pronounced decrease of the Kondo temperature (TK), from ≈50 K in pure CeTiGe to less than 4 K at large La content. Since the former value is of the order of the crystal field splitting, while the latter is well below, the systems evolves from a large degeneracy N = 6 Kondo system at x = 0 to a conventional N = 2 Kondo system at x ≥ 0:8. There, the first excited crystal field doublets become apparent in the T dependence of the specific heat CP(T) at an excitation energy DCF ≈ 30 K. The reduction of the degeneracy is expected to enhance the decrease of TK, explaining the strong reduction by more than one order of magnitude observed in this system. The decrease of TK drives the system toward QC as evidenced by a divergence of CP(T)/T and x(T) toward low temperatures in the x = 0:8 sample. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Sereni, J. G., M. Gómez Berisso, G. Schmerber, and J. P. Kappler. "Suppression of the Shastry-Sutherland phase in Ce2 Pd 2 Sn at a field-induced critical point." Physical Review B – Condensed Matter and Materials Physics 81, no. 18 (2010): 184429.
Abstract: The magnetic phase diagram of Ce2 Pd2 Sn is investigated through the field dependence of thermal, transport, and magnetic properties at low temperature. The upper transition, TM =4.8 K is slightly affected by magnetic field up to B=1 T whereas the lower one T C (B) rapidly increases from 2.1 K joining TM in a critical point at Tcr = (4.1±0.2) K for Bcr = (0.11±0.01) T. At that point, the intermediate phase, previously described as an unstable Shastry-Sutherland lattice, is suppressed. A detailed analysis around the critical point reveals a structure in the maximum of the ∂ M/∂ B (B) derivative, which may be related to a step in magnetization predicted by theory for the mentioned lattice. © 2010 The American Physical Society.
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Sirena, M., A. Zimmers, N. Haberkorn, E. E. Kaul, L. B. Steren, J. Lesueur, T. Wolf, Y. Le Gall, J. - J. Grob, and G. Faini. "Direct observation of electronic inhomogeneities induced by point defect disorder in manganite films." Journal of Applied Physics 107 (2010): 113903.
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