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Causa, M. T., S. M. Dutrús, C. Fainstein, G. Nieva, H. R. Salva, R. D. Sánchez, L. B. Steren, M. Tovar, and Zysler R. "MAGNETIC AND STRUCTURAL PROPERTIES OF SOME ABa2Cu3O7?? SUPERCONDUCTORS." International Journal of Modern Physics B 1, no. 3-4 (1987): 989–992.
Abstract: We report here normal and superconducting properties of ABa2Cu3O7?? (with A=Y, Gd, Dy, and Er) and of Fe doped YBa2Cu3O7??. Results from X-ray powder diffraction, electrical resistivity, magnetic susceptibility, ESR, and specific heat measurements are presented, leading to a characterization of the magnetic properties of these materials. The effect of structural modifications of the lattice on the superconducting properties and the relative insensitivity of Tc to the presence of magnetic moments is discussed.
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Causa, M. T., C. Fainstein, G. Nieva, R. S\'anchez, L. B. Steren, M. Tovar, R. Zysler, D. C. Vier, S. Schultz, S. B. Oseroff et al. "Crystal-field interaction in the GdxEu1-xBa2Cu3O7-? superconductors." Physical Review B 38 (1988): 257–261.
Abstract: We report here experimental data on the crystal-field interaction of gadolinium ions with their environment in GdxEu1-xBa2Cu3O7-?. The ESR spectrum and a Schottky anomaly in the specific heat of dilute samples (x?1) indicate the existence of a crystal-field splitting of the 8S7/2 ground state of Gd3+ ions of about 1.5 K. We discuss the parametrization of the measured splitting in terms of an effective Hamiltonian, and the microscopic origin of the interaction within the framework of a superposition model. Since the single-ion energies involved are of the same order of magnitude as the energies associated with the magnetic ordering of the Gd3+ moments in GdBa2Cu3O7-? (TN?2.24 K), we analyze the effects of the crystal-field interaction on the magnetic transition.
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Causa, M. T., S. M. Dutrus, C. Fainstein, G. Nieva, R. Sanchez, L. B. Steren, M. Tovar, R. Zysler, S. B. Oseroff, D. C. Vier et al. "Magnetic ordering in dilute GdxEu1−xBa2Cu3O7−δ superconductors." Physica C: Superconductivity 153 (1988): 188–189.
Abstract: We have measured the specific heat of GdxEu1−xBa2Cu3O7−δ (0 ≤ × ≤ 1). The data show a λ-type anomaly at high concentrations and a broad Schottky type anomaly at intermediate and low concentrations. We compare this behavior with theoretical predictions for a 2-dimensional Ising system.
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Causa, M. T., C. Fainstein, G. Nieva, R. Sánchez, L. B. Steren, M. Tovar, R. Zysler, D. C. Vier, S. Schultz, S. B. Oseroff et al. "Crystal Field Interaction and Magnetic Order in GdBa2Cu3O7." In Progress in High Temperature Superconductivity, edited by J. L. Heiras. Vol. 5. N.J.: World Scientific, 1988.
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Durán, C., P. Esquinazi, C. Fainstein, and M. Núñez Regueiro. "Anomalies in the internal friction and sound velocity in YBa2Cu3O7-x and EuBa2Cu3O7-x superconductors." Solid State Communications 65, no. 9 (1988): 957–961.
Abstract: Internal friction Q-1 and Young Modulus sound velocity vE measurements at 1 kHz in YBa2Cu3O7?x and EuBa2Cu3O7?x polycrystalline samples reveal anomalies at the superconducting transition and at not, vert, similar37 K. The anomaly in vE at not, vert, similar90 K is accompanied by an absorption peak and is in agreement with published ultrasonic measurements, suggesting a lattice deformation at the superconducting transition.
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Esquinazi, P., C. Durán, C. Fainstein, and M. Núñez Regueiro. "Evidence of low-energy tunneling excitations in the high-Tc superconductor YBa2Cu3O7-x." Physical Review B 37, no. 1 (1988): 545–547.
Abstract: We have measured the internal friction Q-1 and the Young's-modulus sound velocity vE at 1 kHz for YBa2Cu3O7-x. Below 20 K the relative change in the sound velocity and the temperature dependence of the internal friction perfectly resemble the behavior obtained for Suprasil W. Below 1 K we observe a logarithmic temperature dependence for the sound velocity and between 1 and 5 K a well-defined plateau in the internal friction is obtained. We find quantitative agreement with the predictions of the standard tunneling model which is widely used to explain the low-temperature properties of amorphous materials. The implications of the existence of tunneling systems in these materials are discussed.
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Izbizky, M. A., M. Núñez Regueiro, P. Esquinazi, C. Durán, and C. Fainstein. "Phonon transport in superconducting EuBa2Cu3O7-x." Physics Letters A 129, no. 1 (1988): 71–75.
Abstract: We have measured the thermal conductivity, Young modulus sound velocity and internal friction of a polycrystalline sample of the ceramic superconductor EuBa2Cu3O7-x. The low temperature data can be quantitavely understood assuming the interaction of phonons with tunneling systems.
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Izbizky, M. A., M. Núñez Regueiro, P. Esquinazi, and C. Fainstein. "Thermal conductivity and superconductivity in EuBa2Cu3O7-x." Physical Review B 38, no. 13 (1988): 9220–9223.
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Massa, N. E., I. Rasines, G. Nieva, J. A. Campá, and C. Fainstein. "Far infrared transmission spectra of Bi2Sr2Ca1(Cu1−x,Znx)2O8+δ, 0.0≤x≤0.05, crystallites in the normal state: Detection of superconducting gap precursors." Physica C: Superconductivity 235-240, no. 2 (1994): 1065–1066.
Abstract: We report transmission spectra of crystallites, taken from single crystal specimens of two plane Bi2Sr2Ca1(Cu1−x,Znx)2O8+δ, 0.0≤x≤0.05, diluted in CsI or polyethylene matrices In addition to weaker features assigned to unscreened phonons and a continuous background probably due to carriers, we found that the ratios of room temperature spectra to those taken lowering the temperature in 50 degrees intervals signal the presence of superconducting gap behavior with 2Δ/kBTc6. We verified this by down shifting frequency as a function of Zn increment and the lowering of Tc induced by this strong superconductivity suppressor. Our preliminary search for phonons self-energy effects close to the superconducting transition temperature gave negative results.
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Massa, N. E., J. Campa, I. Rasines, C. Fainstein, and G. Nieva. "Superconducting order parameter and the phonon profile in the bismuth family of compounds." Anales de la Asociación Química Argentina 84, no. 1 (1996): 7–12.
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