Magnetic ordering and superconducting in Fe-doped 1-2-3 compounds

Abstract

We have doped Fe into the ground YBa2Cu3O7 and have discovered that the Fe goes primarily into one of the two Cu sites. At least 95% of the Fe substitutes into the Cu(1) site in the Cu-O layers between Ba layers. A high valence state of iron, Fe4+, is found to exist inside this compound. For even small amounts of Fe we see a spin-glass type of magnetic ordering of the Fe spins which we feel is associated with a tendency for antiferromagnetic couplings of the Cu(1) ions. We conclude that the Cu(2)-O2 plane is more important than the Cu(1)-O chain for the superconductivity in the 1-2-3 compounds.