Studies of Nuclear and Magnetic Structures of Y Sr2 Fe3 O7+δ by Neutron-Powder-Diffraction

Neutron diffraction Pattern of Y Sr2 Fe3 O7+δ super-conducting material has been obtained and refined by the Rietveld technique using 'FULLPROF' computer program. The chemical structure resembles that of undoped Y Ba2 Cu3 O7 and may be refined in tetragonal P4/mmm space group. The suitable space group for magnetic structure has found to be I,mmm. The Fe atoms replaced the Cu cations located both in Cu-O chains and in the Cu O2 planes with equal probabilities. The configuration of the unit cell has some dissimilarities with that of the superconductor YBa2 Cu3 O7,Particularly for the iron ions corresponding to the Cu-chain ions have octahedral coordination, rather than square planar. The octahedra thus are arranged in layer rather than in chains. This significant difference is a consequence of the fact that the possible oxygen sites in these layers are eight when fully occupied rather than seven atoms per formula unit.The magnetic structure is based on a unit cell related to that of the nuclear structure by an axis transformation of matrix (110/110/002). The iron moments are coupled antiferromagnetically within each Fe O2 layer , as well as along c axis. The magnetic moments of all the iron ions are the same with a value of ∼3.35μB. 5 tables, 3 figs., 24 refs. (Author)