Superconductivity and Magnetic Properties of YBa2(Cu1-xFex)3O7-y

Superconductivity and magnetic properties of YBa 2 (Cu 1- x Fe x ) 3 O 7- y with x =0-0.1 are investigated by the measurements of static magnetic susceptibility, electrical resistance, weight change and lattice parameters. Substitution of Fe atoms for Cu atoms causes orthorhombic to tetragonal phase transition at about x =0.035 and depresses critical temperature T c from 95 K to 32 K at x =0.1. The effective magnetic moment per Fe, about 5.5 µ B below x =0.01 decreases to 3.6 µ B at x =0.1. The removal of oxygen atoms in the specimens of superconducting tetragonal phase with x =0.04 by quenching brings about remarkable expansion of c -axis and decreases T c from 74 K to below 4.2 K. The effective moment per Fe was found to decrease from 4.4 µ B to 3.3 µ B with increase of oxygen deficiency due to quenching. Causes of reduced iron effective moments due to increase of iron concentration and oxygen deficiency are discussed in consideration of superexchange interaction between Fe and Cu spins.