Crystal-field interaction in the GdxEu1-xBa2Cu3O7-δ superconductors

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 (x1) indicate the existence of a crystal-field splitting of the S728 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. © 1988 The American Physical Society