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Ćtem Acceso Abierto Longitudinal Magnetomorphic Effect in Indium Films(American Physical Society, 1967-11-15) de la Cruz, F.; de la Cruz, M.E.; Cotignola, J.M.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasMeasurements of magnetomorphic effects in indium films of thickness between 0.003 and 0.01 cm have been made at 4.2 and 1.5Ā°K. The results were compared with theoretical calculations based on the free-electron model. To make these comparisons, it was necessary to discount the bulk magnetoresistance by means of a modified Kohler's rule suggested by Olsen. From the comparison of the data with the theory, it was possible to deduce the values of the electronic momentum mv and the product of the bulk resistivity with the bulk mean free path Ļbl. Data previously obtained by Olsen in wires have been analyzed with the use of measurements of Kohler's rule and of a criterion for the comparison different from the one used by Olsen. The experimental value of Ļbl is discussed on the basis of an analysis made by Bate et al., in which the anisotropy of the mean free path is taken into account.Ćtem Acceso Abierto Thermal and Electrical Conductivities of Very-High-Purity Indium(American Physical Society, 1968-12-00) de la Cruz, M.E.; Cotignola, J.M.; Bressan, O.J.; Luengo, C.A.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasMeasurements of the thermal and electrical conductivities of a polycrystalline indium sample of very high purity have been performed between 1.5 and 4.2Ā°K and in the presence of longitudinal magnetic fields up to 15 000 Oe. It was found that, within the experimental error, the electrical and thermal Kohler's rules were satisfied, the functional forms for the two being quite similar. The expression for the resistivity as a function of T for the normal state and in zero magnetic field are in good agreement with theory. The Lorenz number obtained by extrapolating to T=0 gives a very high value compared with the theoretical one. Measurements of the thermal conductivity for the superconducting state, in the same temperature range, have been made. The thermal-resistivity ratio WnWs as a function of the reduced temperature does not agree with the results of Kadanoff and Martin.Ćtem Acceso Abierto Experimental Heat Capacity of Pure Liquid He3(American Physical Society, 1969-09-00) Mota, A.C.; Platzeck, R.P.; Rapp, R.; Wheatley, J.C.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasMeasurements of the heat capacity of pure He3 at 0.24 atm obtained by a differencing method are presented for the temperature range from 20-150 mĀ°K. The temperature scale Tā used is that valid for powdered cerium magnesium nitrate in the form of a right circular cylinder with diameter equal to height. There is excellent agreement between the present and earlier measurements. Considering all low-pressure difference data we find that from 6-125 mĀ°K the ratio of heat capacity to magnetic temperature decreases linearly with increasing temperature. The relationship of the measurements to the temperature scale and to theories of spin fluctuations in He3 is also discussed.Ćtem Acceso Abierto Variation of the Ratio Hc3/Hc2 in the Immediate Vicinity of Tc(American Physical Society, 1969-11-10) de la Cruz, F.; Maloney, M.D.; Cardona, M.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasWe have measured the ratio Hc3Hc2 for tin-rich Sn-In alloys and for indium-rich In-Bi alloys in the immediate vicinity of Tc. For the Sn-In system this ratio decreases as Tc is approached. Similar behavior has been recently reported by Ostenson and Finnemore for pure Nb. The In-Bi alloys, however, show a marked increase in Hc3Hc2 as the critical temperature is approached.Ćtem Acceso Abierto Low-Temperature Specific Heats of the beta and zeta Phases in Equiatomic AgZn(American Physical Society, 1970-09-15) Abriata, J. P.; Bressan, O. J.; Luengo, C. A.; Thoulouze, D.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasHeat-capacity measurements between 1.3 and 4.2Ā°K have been made on equiatomic AgZn in both the Ī²ā² and Ī¶0 phases. Significant differences were found in the Debye temperature and the electronic specific-heat coefficient, the latter data being discussed in terms of Fermi-surface-Brillouin-zone interactions. Furthermore, it is concluded that Ī²ā² is the stable phase at 0Ā°K, and that in this particular alloy, vibrational properties are of major importance in controlling phase stability near 0Ā°K.Ćtem Acceso Abierto Anomalous Behavior of Hc3/Hc2 near Tc for Sn-In and In-Bi Alloy Systems(American Physical Society, 1970-10-01) Maloney, M.D.; de la Cruz, F.; Cardona, M.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasPreviously reported measurements of the ratio Hc3Hc2 for tin-rich Sn-In alloys and indium-rich In-Bi alloys have been extended in further detail, and include variations in foil thickness (6 - 300 Ī¼). The anomalous behavior in the ratio very near Tc is found to be dependent on foil thickness. Each alloy system is characterized by a certain thickness, above which Hc3Hc2 decreases markedly as Tc is approached, and below which the opposite behavior takes place. The results can be interpreted qualitatively in terms of a sandwich model in which the strength of the pairing interaction is depressed in a layer at the surface of the sample. For the thickest samples (most nearly "semi-infinite"), there is good quantitative agreement with the recent theory of this proximity effect given by Fink and Presson.Ćtem Acceso Abierto Superconductive Supercooling and Superheating of Small Cadmium Spheres: Size Effects(American Physical Society, 1971-06-01) de la Cruz, F.; Maloney, M.D.; Cardona, M.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasSupercooling and superheating have been observed for samples composed of small cadmium spheres of uniform well-defined sizes. The data obtained for large sphere diameters are independent of size and represent, by all indications, ideal bulk properties. The supercooling data for such spheres have been used to obtain the Ginsburg-Landau parameter Īŗ and, in conjunction with BCS expressions, the penetration depth Ī» and the coherence length Ī¾0. The temperature dependence of the supercooling field Hsc shows an anomaly for tā¼0.8, very similar to that previously reported for Al and Zn. The superheating field of these "bulk" spheres shows strong effects of the nonlocal electrodynamics below Tc. Spheres of diamters equal to or smaller than 10 Ī¼ show strong size effects in the supercooling and superheating fields, especially near Tc. The results are examined in the light of existing theories of critical fields for small spheres. A systematic decrease of the critical temperature with sphere size has also been observed. It seems related to a decrease in the gap anisotropy, produced by boundary scattering. These results are analyzed in terms of the theory of Markowitz and Kadanoff.Ćtem Acceso Abierto Superconducting Parameters and Size Effects of Aluminum Films and Foils(American Physical Society, 1972-05-01) Maloney, M.D.; de la Cruz, F.; Cardona, M.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasIn this paper we present the experimental results and analysis of the critical-field determination of aluminum films and foils. We studied the thermodynamic parallel and perpendicular critical fields as a function of thickness and temperature. The measurement of the critical fields together with suitable theories allows the determination of the penetration depth Ī», the coherence length Ī¾, and the surface-energy parameter Ī. The thermodynamic transition of all films studied was of second order. Measurement in both magnetic field orientations offers a check on the consistency of the methods used to analyze the data. The value of the Ginzburg-Landau parameter Īŗ obtained from these measurements is six times larger than the value obtained from supercooling experiments. This phenomenon has been observed previously by other authors in different metals. The superconducting transition of all foil samples was of first order. In perpendicular fields the transition to the intermediate state was analyzed by means of an interpolation formula having the correct theoretical behavior in the limits of both large and small thicknesses. The value of the surface-energy parameter so obtained is in agreement with the supercooling result.Ćtem Acceso Abierto Low angle electron scattering in thermal resistivity(IOP Publishing, 1975-00-00) Bressan, O.J.; Ridner, A.E.; de la Cruz, F.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasElectrical ( rho ) and thermal (W) resistivity measurements in very dilute In alloys between 1K and 4K show a temperature dependence expressed by rho = rho 0+ beta T5 and WT=(WT)0+AT3+BT5. The BT5 term in the thermal resistivity is due to a contribution from a 'diffusion-like process' of electrons over the Fermi surface, as is the one that describes the temperature dependence of the electrical resistivity. This claim is supported by the experimental fact that the Lorenz number defined as L= beta /B coincides with the value given by L= rho 0/(WT)0 which in turn agrees with the free electron value within 15%.Ćtem Acceso Abierto T5 law and Matthiessen's rule(IOP Publishing, 1975-00-00) Bressan, O.J.; Ridner, A.E.; de la Cruz, F.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasPrecise electrical resistivity measurements on very dilute non magnetic indium alloys show no doubt in a T5 dependence on temperature between 1-4K and strong deviations from Matthiessen rule. Measurements of thermal resistivity show that the extrapolation method to obtain the data to H=0 is correct. Comparison of the results with recent theories is discussed.Ćtem Acceso Abierto Surface-Temperature Determination in the Kapitza Problem(American Physical Society, 1975-09-29) Ridner, A.; MartĆnez, E. N.; de la Cruz, F.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasIt is shown that surface superconductivity can be used as a localized thermometer. Its application to the study of the thermal boundary resistance at a Pb-4He interface provides the first experimental evidence for the existence of a rapid temperature variation within microscopic distances from the surface.Ćtem Acceso Abierto Low temperature specific heat of Th-Gd spin glass(Elsevier, 1979-03-00) Sereni, J.G.; Huber, T.E.; Luengo, C.A.The specific heat measurements of T-Gd alloys, with Gd concentration ranging from 0.15% to 10.8% and temperatures between 0.4 and 8 K, are reported. The characteristic spin glass specific heat enhancement and its maximum was found linearly proportional to Gd concentration. At low temperatures a T2 dependence of the specific heat was observed and the entropy associated with the magnetic ordering was the 70% of the expected value for the spin S=72.Ćtem Acceso Abierto Interconfigurational fluctuations in Ce cubic compounds(EDP Sciences, 1979-05-00) Sereni, J.G.; Olcese, G.L.; Rizzuto, C.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasThe magnetic susceptibility of thirty Ce cubic compounds is analyzed, assuming a temperature dependence of the valence fluctuations. The energy level scheme, obtained by fitting the measured susceptibility is used to calculate other physical properties. A correlation between the Ce ionic radius and the interconfigurational excitation energy has been found.Ćtem Acceso Abierto Temperature dependence of the superconducting giant-vortex state. Theory and Experiment(American Physical Society, 1979-09-01) de la Cruz, F.; Fink, H.J.; Luzuriaga, J.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasWhen a type-I superconductor with a surface nucleation field Hc3(T)>Hc(T) (thermodynamic critical field) is thermally cycled in an axially applied magnetic field H0 between the temperatures T(Hc3) and about T(Hc), experiments show that the magnetization changes reversibly. The latter is diamagnetic near T(Hc3) but can be paramagnetic just above T(Hc). This behavior is explained by assuming that the fluxoid quantum number b is fixed at the transition from the normal to the superconducting state and retained at lower temperatures. The value of b is determined almost entirely by the flux at the transition which is enclosed by a contour located at a distance Ī¾1.7 from the surface inside the cylinder (Ī¾ is the coherence length). The temperature variation of the order parameter f at the surface of the cylinder, the magnetization m, and the temperature at which m=0 for fā 0 are calculated for Rā«Ī¾. Conservation of the fluxoid quantum number, while T is varied causes the two opposing surface currents to become imbalanced. This is the source of the observed para- and diamagnetism.Ćtem Acceso Abierto Evidence for valence fluctuation in the CeSn3 compound(IOP Publishing, 1980-00-00) Sereni, J.G.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasPresents the experimental results of magnetisation, magnetic susceptibility (at normal pressure and under a pressure of 6 kbar), electrical resistivity and thermal expansion performed on a single sample of CeSn3. These measurements were done over the temperature range of 1.4Ćtem Acceso Abierto Phase diagram and superconductive properties of splat-cooled CuxLa1-x(American Physical Society, 1980-04-01) Favaron, J.; de la Cruz, M.E.; Esquinazi, P.; de la Cruz, F.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasThe phase diagram of nonequilibrium, splat-cooled CuxLa1āx is interpreted by means of superconductive-transition and x-ray measurements. At the eutectic composition the material is shown to be in a highly disordered state. Measurements of dc resistance and ac susceptibility show that there are two different critical fields at the disordered concentration although there is a unique critical temperature.Ćtem Acceso Abierto Superconducting penetration depth in amorphous La70Cu30(Elsevier, 1981-00-00) Arce, R.; de la Cruz, F.; Esquinazi, P.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasIt is shown that weak field penetration depth measurements can be used to determine the change in the normal and superconducting behaviour of amorphous samples, when heat-treated below the crystallization temperature. The results are used to discuss the validity of BCS-Gorkov relations, when applied to these materials.Ćtem Acceso Abierto Superconducting penetration depth in amorphous metals(Elsevier, 1981-06-00) Arce, R.; de la Cruz, F.; Esquinazi, P.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasWe show that temperature dependent penetration depth measurements can be used to characterize the superconductive behaviour of amorphous metals.Ćtem Acceso Abierto Model relating superconductive penetration depth and metallurgical phase separation in amorphous La70Cu30(Elsevier, 1982-05-00) Arce, R.; de la Cruz, F.; Fink, H.J.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasA model is proposed to account for the large increase in the measured penetration depth of superconducting, amorphous La70Cu30 when the specimens are annealed sufficiently long near, but below, the crystallization temperature. It is suggested that a metallurgical phase separation occurs with domain dimensions in the submicrometer range. Penetration depth measurements as a function of temperature in a weak magnetic field are a useful tool to detect changes in phase separation in high-K materials.Ćtem Acceso Abierto Phonon thermal conductivity limited by electron scattering in amorphous Zr70Cu30(American Physical Society, 1983-03-01) Esquinazi, P.; de la Cruz, F.; Gerencia FĆsica. Departamento Materia Condensada. DivisiĆ³n Bajas TemperaturasThe low-temperature thermal conductivity of amorphous Zr70Cu30 is investigated. The lattice thermal conductivity as limited by electrons in the superconducting state has been obtained at temperatures close to Tc. This has allowed for the first time the verification of the temperature dependence of the phonon conductivity as predicted by Bardeen, Rickayzen, and Tewordt. The analysis of the data in the normal and superconducting state shows that Matthiessen's rule can be used in amorphous metals to separate the different scattering processes.