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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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Chan, I. N., D. C. Vier, O. Nakamura, J. Hasen, J. Guimpel, S. Schultz, and I. K. Schuller. "Thickness dependence of the superconducting transition temperature of YBCO." Physics Letters A 175, no. 3-4 (1993): 241–245.
Abstract: We have performed detailed structural and superconducting studies of YBCO single layers, YBCO/PrBCO/YBCO tri-layers, and YBCO/PrBCO superlattices. The results for single layers indicate that a nominally one unit cell thick YBCO film sandwiched between PrBCO layers is not superconducting. However, a superlattice with nominally one unit cell thick YBCO layers has a measurable superconducting temperature onset (Tco). These apparently contradictory results are reconciled by experiments on YBCO/PrBCO/YBCO tri-layers which, due to coupling across the PrBCO insulating layer, exhibit superconductivity for PrBCO thicknesses below 200 Ã…. Structural studies show that the length scale of the superconductive coupling is much larger than the length scale of the step disorder and interdiffusion present in the film.
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