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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