Structural and magnetic transitions in YBa2(Cu1-xFex)(3)O-y

The structural, electronic, and magnetic transitions induced by oxygen reduction in the YBa2(Cu1-xFex)(3)O-y superconductors (SC) have been studied by the neutron diffraction and Mossbauer spectroscopy on the same Fe-57 isotope enriched samples. It was found that the local crystal structure, charge and spin states of all ions in the Cu1 layers change remarkably upon the reduction. Magnetic ordering of Fe ions, existing at low temperature in both Cu1 and Cu2 sites of the SC samples, is a short-range or spin-glass order. In the reduced non-SC samples, the long-range AF order exists in both Cu1 and Cu2 sublattices, and a crossover of dimensionality of the magnetic order in the Cu1 lattice is observed at intermediate temperatures.