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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Morhell, N., and H. Pastoriza. "A single channel capillary microviscometer." Microfluidics and Nanofluidics 15, no. 4 (2013): 475–479. http://dx.doi.org/10.1007/s10404-013-1162-4 (accessed October 31, 2020).
Abstract: We have developed a microviscometer analyzing the fluid dynamics in a single
channel glass microfluidic chip with a closed end. The device is able to test sample
volumes of a few microliters by inserting one drop in the inlet. The fluid enters the
channel driven by capillary pressure and an optical sensor registers the motion. The
equation that describes the fluid dynamics is function of the channel geometry,
atmospheric pressure, fluid viscosity and capillary pressure. Knowing the first two the
last parameters can be obtained as fitting parameters from the meniscus position as a
function of time plot. We have successfully tested Newtonian fluids with different
viscosities and capillary pressure.
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Osquiguil, E., L. Tosi, E. E. Kaul, and C. A. Balseiro. "On the origin of the low temperatures resistivity minimum in Cr thin films." Journal Of Applied Physics 114, no. 24 (2013): 7 pp.
Abstract: We present measurements of the electrical resistivity and Hall coefficient, p and R-H, in Cr films of different thicknesses grown on MgO (100) substrates, as a function of temperature T and applied magnetic field H. The results show a low temperature minimum in rho(T), which is thickness dependent. From 40K to 2K, the Hall coefficient is a monotonous increasing function as T is reduced with no particular signature at the temperature T-min, where the minimum develops. We explain the resistivity minimum assuming an imperfect nesting of the Fermi surface leading to small electron and hole pockets. We introduce a phenomenological model which supports this simple physical picture. (C) 2013 AI Publishing LLC.
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S. Demirdis, Y. Fasano, S. Kasahara, T. Terashima, T. Shibauchi, Y. Matsuda, M. Konczykowski, H. Pastoriza and C. J.Van Der Beek. "Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe2(As1-xPx)2." Physical Review B 87, no. 9 (2013): 094506–11.
Abstract: We present a comprehensive overview of vortex pinning in single crystals of the isovalently substituted iron-based superconductor BaFe2(As1−xPx)2, a material that qualifies as an archetypical clean superconductor, containing only sparse strong pointlike pins [ C. J. van der Beek et al. Phys. Rev. B 66 024523 (2002)]. Widely varying critical current values for nominally similar compositions show that flux pinning is of extrinsic origin. Vortex configurations, imaged using the Bitter decoration method, show less density fluctuations than those previously observed in charge-doped Ba(Fe1−xCox)2As2 single crystals. Analysis reveals that the pinning force and energy distributions depend on the P content x. However, they are always much narrower than in Ba(Fe1−xCox)2As2, a result that is attributed to the weaker temperature dependence of the superfluid density on approaching Tc in BaFe2(As1−xPx)2. Critical current density measurements and pinning force distributions independently yield a mean distance between effective pinning centers LÌ… ∼90 nm, increasing with increasing P content x. This evolution can be understood as being the consequence of the P dependence of the London penetration depth. Further salient features are a wide vortex free “Meissner beltâ€, observed at the edge of overdoped crystals, and characteristic chainlike vortex arrangements, observed at all levels of P substitution.
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Sereni, J. G. "Thermodynamic analysis of the quantum critical behavior of Ce-lattice compounds." Philosophical Magazine 93, no. 4 (2013): 409–433.
Abstract: A systematic analysis of low-temperature magnetic phase diagrams of Ce compounds is performed in order to recognize the thermodynamic conditions to be fulfilled by those systems to reach a quantum critical regime or, alternatively, to identify other kinds of low-temperature behavior. Based on specific heat (C m ) and entropy results, three different types of phase diagrams are recognized: (i) with the entropy involved in the ordered phase (S MO) decreasing proportionally to the ordering temperature (T MO); (ii) those showing a transference of degrees of freedom from the ordered phase to a non-magnetic component, with their C m (T MO) jumps (ΔC m ) vanishing at finite temperature; and (iii) those ending at a critical point at finite temperature because their ΔC m do not decrease sufficiently with T MO, producing an entropy accumulation at low temperature. Only those systems belonging to the first case, i.e. with S MO → 0 as T MO → 0, can be regarded as candidates for quantum critical behavior. Their magnetic phase boundaries deviate from the classical negative curvature below T ≈ 2.5 K, denouncing monotonic misleading extrapolations down to T = 0. Different characteristic concentrations are recognized and analyzed for Ce-ligand alloyed systems. In particular, a pre-critical region is identified where the nature of the magnetic transition undergoes significant modifications, with its ∂C m /∂T discontinuity strongly affected by the magnetic field and showing an increasing remnant entropy at T → 0. Physical constraints arising from the third law at T → 0 are discussed and recognized from experimental results.
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Sereni, J. G., G. Schmerber, and J. P. Kappler. "Thermodynamic Behavior of Ce Compounds Close to a T->0 Critical Point." IEEE Transactions on Magnetics 49, no. 8 (2013): 4647–4651.
Abstract: There is a reduced group of Ce very heavy Fermions (VHF) which do not order magnetically down to at least T ≈ 500 mK because they are very close to a Tord = 0 critical point. These compounds are at the top of the limT→ 0 Cm/T specific heat values because they collect very high density of low energy excitations. From the analysis of Cm(T)/T and entropy Sm(T) dependencies performed on selected CePd3Mx ternaries (where M = B and Be) a quantitative evaluation of an upper limit for the density of excitations can be proposed. These observations exclude any evidence of Cm(T)/T divergency as T→ 0 in agreement with thermodynamic laws. A comparison with selected Yb-base VHF supports these features.
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van der Beek, C. J., S. Demirdis, D. Colson, F. Rullier-Albenque, Y. Fasano, T. Shibauchi, Y. Matsuda, S. Kasahara, P. Gierlowski, and M. Konczykowski. "Electron irradiation of Co, Ni, and P-doped BaFe2As2–type iron-based superconductors." In Journal of Physics: Conference Series, 012023. Vol. 449., 2013.
Abstract: High energy electron irradiation is used to controllably introduce atomic-scale point defects into single crystalline Ba(Fe1−xCox)2As2, Ba(Fe1−xNix)2As2, and BaFe2(As1−xPx)2. The appearance of the collective pinning contribution to the critical current density in BaFe2(As1−xPx)2, and the magnitude of its enhancement in Ba(Fe1−xCox)2As2, conform with the hypothesis of quasi-particle scattering by Fe vacancies created by the irradiation. Whereas the insignificant modification of the temperature dependence of the superfluid density in Ba(Fe1−xCox)2As2 and Ba(Fe1−xNix)2As2 points to important native disorder present before the irradiation, the critical temperatures of these materials undergo a suppression equivalent to that observed in the much cleaner BaFe2(As1−xPx)2. This lends credence to the hypothesis of line nodes of the order parameter (at finite kz) in the former two materials.
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Yadav, C. S., G. Seyfarth, P. Pedrazzini, H. Wilhelm, R. Cerný, and D. Jaccard. "Effect of pressure cycling on Iron: Signatures of an electronic instability and unconventional superconductivity." Physical Review B 88, no. 5 (2013): 054110–7.
Abstract: High pressure electrical resistivity and x-ray diffraction experiments have been performed on Fe single crystals. The crystallographic investigation provides direct evidence that in the martensitic $bcc \rightarrow hcp$ transition at 14 GPa the $\lbrace 110\rbrace{bcc}$ become the $\lbrace 002\rbrace{hcp}$ directions. During a pressure cycle, resistivity shows a broad hysteresis of 6.5 GPa, whereas superconductivity, observed between 13 and 31 GPa, remains unaffected. Upon increasing pressure an electronic instability, probably a quantum critical point, is observed at around 19 GPa and, close to this pressure, the superconducting $T{c}$ and the isothermal resistivity ($0<T<300\,$K) attain maximum values. In the superconducting pressure domain, the exponent $n = 5/3$ of the temperature power law of resistivity and its prefactor, which mimics $T{c}$, indicate that ferromagnetic fluctuations may provide the glue for the Cooper pairs, yielding unconventional superconductivity.
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Zemma, E., and J. Luzuriaga. "Anomalous Trajectories of H2 Solid Particles Observed Near a Sphere Oscillating in Superfluid Turbulent 4He." Journal of Low Temperature Physics 173, no. 1-2 (2013): 71–79.
Abstract: Using a relatively low cost apparatus, consisting of a glass dewar and a digital camera capable of taking images at 240 frames per second we have observed trajectories of frozen H2 particles which follow the flow of liquid helium below 2 K, around a sphere oscillating at 38 Hz. In some of the images the motion is compatible with laminar flow, while at high amplitudes, where we can reach Reynolds numbers of a few thousand in the normal component, the flow is clearly turbulent. In some of the videos taken we find particles being suddenly accelerated to several times the velocity of the oscillating sphere.
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Zemma, E., and J. Luzuriaga. "Turbulent Flow Around an Oscillating Body in Superfluid Helium: Dissipation Characteristics of the Nonlinear Regime." Journal of Low Temperature Physics 172, no. 3-4 (2013): 256–265.
Abstract: By examining the resonance curves of an oscillator submerged in superfluid liquid helium, it is found that their shape is affected by two distinct dissipation regimes when the amplitude is large enough to generate turbulence in the liquid. In a resonance curve, the central part close to resonance, may be in a turbulent regime, but the response is of much lower amplitude away from the resonance frequency, so that the oscillation can still be in the linear regime for frequencies not exactly at resonance. This introduces an ambiguity in estimating the inverse quality factor Q −1 of the oscillator. By analyzing experimental data we consider a way of matching the two ways of estimating Q −1 and use the information to evaluate the frictional force as a function of velocity in a silicon paddle oscillator generating turbulence in the superfluid.
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