Abstract
The local magnetic, electronic, and structural properties of (RE)Ba2Cu3O7−δ supercondcutors (RE=Gd, Dy, and Eu) were studied by Mossbauer spectroscopy using the resonances of155Gd,161Dy,151Eu, and57Eu. In GdBa2Cu3O7−δ, different magnetic ordering behaviors of the Gd sublattice are found for the orthorhombic (superconducting) and tetragonal (non-superconducting) phases. In DyBa2Cu3O7−δ, the magnetic moments of the respective CEF ground states in the orthorhombic and tetragonal phases are derived from paramagnetic hyperfine splittings at 1.4 K. In both DyBa2Cu3O7−δ and EuBa2Cu3O7−δ, anomalies connected with the superconducting transitions in isomer shift, recoil-free fraction, and relaxation behavior were looked for, but not found. The electric-quadrupole splittings observed for both systems are discussed in connection with the lattice EFGs derived for the Gd system. In GdBa2 (Cu0.995Fe0.005)3O7−δ, the local properties of the various Fe sites are investigated over a wide temperature range in both the orthorhombic and tetragonal phase. The magnetic ordering of the Gd sublattice in the orthorhombic phase and of the Cu(2) sublattice in the tetragonal phase, respectively, is monitored via the magnetic splittings at the various Fe sites. Possible assignments of Cu(1) and Cu(2) sites as well as different oxygen configurations around the substituted Fe ions are discussed.
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