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Belussi, C. H., M. G. Berisso, and Y. Fasano. "Note: Single-polarity high-voltage amplifier to drive coarse-approach slip-stick piezoelectric motors." Review of Scientific Instruments 84, no. 5 (2013): 056104–3.
Abstract: Scanning probe microscopies typically rely on coarse-approach slip-stick piezoelectric motors that work by exciting piezoelectric stacks with sawtooth signals of hundreds of V and some kHz. For this application, we introduce a single-polarity high-voltage amplifier based on discrete MOSFET-technology components with improved output current desirable for low-temperature actuation. The amplifier has an output signal of 600 V, 100 mA output current, noise level below 2 μV/math, 4 kHz high-voltage bandwidth, 2 V/μs slew-rate, and rise and fall times of 80 μs (when loaded with 30 nF). The circuit was successfully applied to drive a home-made scanning tunnelling microscope.
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Encina, S., and P. Pedrazzini. "Poder termoeléctrico del Ce(Pd1-xCux)2Si2." In Anales de la Asociacion Fisica Argentina, 43–46. Vol. 24., 2013.
Abstract: Se presenta un estudio del poder termoeléctrico, S(T), a bajas temperaturas de la aleación Ce(Pd1-xCux)2Si2. Las curvas deS(T) tienen una dependencia similar en todo el rango de sustitución, con tres anomalÃas: un máximo positivo de altatemperatura, un mÃnimo negativo y un máximo de bajas temperaturas. Se discute brevemente el origen de las anomalÃas,para lo cual se compara S(T) con datos de resistividad eléctrica provenientes de la literatura. Para realizar las medicionesde poder termoeléctrico se diseñó y construyó un dispositivo que puede ser montado en diversos crióstatos.
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Facio, J. I., A. Abate, J. Guimpel, and P. S. Cornaglia. "Vortex kinks in superconducting films with periodically modulated thickness." Journal of Physics: Condensed Matter 25, no. 24 (2013): 245701.
Abstract: We report magnetoresistance measurements in Nb films having a periodic thickness modulation. The cylinder shaped thicker regions of the sample, which form a square lattice, act as repulsive centers for the superconducting vortices. For low driving currents along one of the axes of the square lattice, the resistivity Ï increases monotonously with increasing magnetic field B and the Ï– B characteristics are approximately piecewise linear. The linear Ï versus B segments change their slope at matching fields where the number of vortices is an integer or a half integer times the number of protruding cylinders in the sample. Numerical simulations allow us to associate the different segments of linear magnetoresistance to different vortex-flow regimes, some of which are dominated by the propagation of discommensurations (kinks).
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Franco, D. G., R. E. Carbonio, E. E. Kaul, and G. Nieva. "Tailoring the ground state of the ferrimagnet La2Ni(Ni1/3Sb2/3)O6." Journal of Magnetism and Magnetic Materials 346 (2013): 196–202.
Abstract: We report on the magnetic and structural properties of La2Ni(Ni1/3Sb2/3)O6 in polycrystal, single crystal and thin film samples. We found that this material is a ferrimagnet ( T c ≈ 100 K ) which possesses a very distinctive and uncommon feature in its virgin curve of the hysteresis loops. We observe that bellow 20 K it lies outside the hysteresis cycle, and this feature was found to be an indication of a microscopically irreversible process possibly involving the interplay of competing antiferromagnetic interactions that hinder the initial movement of domain walls. This initial magnetic state is overcome by applying a temperature dependent characteristic field. Above this field, an isothermal magnetic demagnetization of the samples yield a ground state different from the initial thermally demagnetized one.
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Franco, D. G., R. E. Carbonio, and G. Nieva. "Change in the Magnetic Domain Alignment Process at the Onset of a Frustrated Magnetic State in Ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 Double Perovskite." IEEE Transactions on Magnetics 49, no. 8 (2013): 4656–4659.
Abstract: We have performed a combined study of magnetization hysteresis loops and time dependence of the magnetization in a broad temperature range for the ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 double perovskite. This material has a ferrimagnetic order transition at ~100 K and at lower temperatures (~20 K) shows the signature of a frustrated state due to the presence of two competing magnetic exchange interactions. The temperature dependence of the coercive field shows an important upturn below the point where the frustrated state sets in. The use of hysteresis data, magnetization versus applied magnetic field, together with the magnetization versus time data provides a unique opportunity to distinguish between different scenarios for the low temperature regime. From our analysis, a strong domain wall pinning results in the best scenario for the low temperature regime. For temperatures larger than 20 K, the adequate scenario seems to correspond to a weak domain wall pinning.
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Franco, D. G., R. E. Carbonio, and G. Nieva. "Magnetic Properties of the Double Perovskites LaPbMSbO6 (M = Mn, Co, and Ni)." IEEE Transactions on Magnetics 49, no. 8 (2013): 4594–4597.
Abstract: New double perovskites LaPbMSbO6, where M2+ = Mn2+, Co2+, and Ni2+, were synthesized as polycrystals by an aqueous synthetic route at temperatures below 1000 °C. All samples are monoclinic, space group P21/n, as it is observed from Rietveld analysis of X-ray powder diffraction patterns. The distribution of M2+ and Sb5+ among the two octahedral sites have 3% of disorder for M2+ = Ni2+, whereas for M2+ = Mn2+ and Co2+ less disorder is found. The three samples have an antiferromagnetic transition, due to the antiferromagnetic coupling between M2 + through super-superexchange paths M2+-O2--Sb5+-O2--M2+. Transition temperatures are low: 8, 10 and 17 K for Mn2+, Co2+, and Ni2 + respectively, as a consequence of the relatively long distances between the magnetic ions M2+. Besides, for LaPbMnSbO6 a small transition at 45 K was found, with ferrimagnetic characteristics, possibly as a consequence of a small disorder between Mn2+ and Sb5+. This disorder would give additional and shorter interaction paths: superexchange Mn2+-O2--Mn2+.
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Franco, D. G., R. E. Carbonio, and G. Nieva. "Synthesis and structural and magnetic characterization of the frustrated magnetic system La2Ni4/3−xCoxSb2/3O6." Journal of Solid State Chemistry 207 (2013): 69–79.
Abstract: We report the synthesis of double perovskites La2Ni4/3−xCoxSb2/3O6 with x=0, 1/3, 2/3 and 1 by a solid state method. Rietveld refinements of X-ray and neutron powder diffraction data show that all samples crystallize in space group P21/n, with almost perfect occupation of the 2d octahedral site with the transition metals, while all Sb5+ are randomly distributed in a 2c octahedral site. The saturation magnetization in hysteresis loops indicates that the samples are ferrimagnetic throughout all the series. Virgin magnetization curves lie outside hysteresis loops at low temperatures and thermal evolution of Hm – defined as the inflection point of these curves – follows the de Almeida–Thouless dependence for x ≠0 . This spin glass like behavior below 30 K is also supported by thermal evolution of the coercivity, which follows an exponential law typical of magnetic clusters, not found in the pure Ni2+ perovskite, x=0 extreme.
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Gil, D. M., G. Nieva, D. G. Franco, M. I. Gómez, and R. E. Carbonio. "Lead nitroprusside: A new precursor for the synthesis of the multiferroic Pb2Fe2O5, an anion-deficient perovskite." Materials Chemistry and Physics 141, no. 1 (2013): 355–361.
Abstract: In order to investigate the formation of multiferroic oxide Pb2Fe2O5, the thermal decomposition of Pb[Fe(CN)5NO] has been studied. The complex precursor and the thermal decomposition products were characterized by IR and Raman spectroscopy, thermal analysis, powder X-ray diffraction (PXRD), scanning electron microscopy and magnetic measurements. The crystal structure of Pb[Fe(CN)5NO] was refined by Rietveld analysis. It crystallizes in the orthorhombic system, space group Pnma. The thermal decomposition in air produces highly pure Pb2Fe2O5 as final product. This oxide is an anion deficient perovskite with an incommensurate superstructure. The magnetic measurements confirm that Pb2Fe2O5 shows a weak ferromagnetic signal probably due to disorder in the perfect antiferromagnetic structure or spin canting. The estimated ordering temperature from the fit of a phenomenological model was 520Â K. The SEM images reveal that the thermal decomposition of Pb[Fe(CN)5NO] produces Pb2Fe2O5 with small particle size.
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Kneidinger, F., H. Michor, E. Bauer, A. Gribanov, A. Lipatov, Y. Seropegin, J. Sereni, and P. Rogl. "Superconductivity and non-Fermi-liquid behavior of La3Pd4Si4 and Ce3Pd4Si4." Physical Review B 88, no. 2 (2013): 024423.
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M. Grisolia, C. J. Van Der Beek, Y. Fasano, A. Forget, D. Colson. "Multifractal scaling of flux penetration in the Iron-based Superconductor Ba(Fe0.925Co0.075)2As2." Physical Review B 87, no. 10 (2013): 104517–8.
Abstract: The penetration of magnetic flux fronts in the optimally doped iron-based superconductor Ba(Fe1−xCox)2As2 (x=0.07±0.005) is studied by means of magneto-optical imaging and Bitter decoration. The higher-order analysis of roughening and growth of the magnetic flux front reveals anomalous scaling properties, indicative of non-Gaussian correlations of the disorder potential. While higher-order spatial correlation functions reveal multifractal behavior for the roughening, the usual Kardar-Parisi-Zhang growth exponent is found. Both exponents are found to be independent of temperature. The scaling behavior is manifestly different from that found for other modes of flux penetration, such as that mediated by avalanches, suggesting that multiscaling is a powerful tool for the characterization of roughened interfaces. We propose a scenario for vortex penetration based on two-dimensional percolation and cluster aggregation for an inhomogeneously disordered superconductor.
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