Superconductivity and spin-glass ordering in RBa2 (Cu1−xFex)3Oz: R=Y,Gd; 0≤x≤0.12

Abstract

Samples of oxygen deficient perovskites, YBa₂ (Cu_1−x Fe_x )₃O_z and GdBa₂ (Cu_1−x Fe_x )₃ O_z (z≂7) were prepared with up to 12% Fe substituting for Cu. A novel variation of the microwave absorption technique was employed to establish the superconducting transition in these samples and to show that the reduction in the transition temperature with increasing Fe concentration is faster in the Gd samples than in the Y ones. In both series of samples, the room‐temperature Mössbauer spectra reveal two distinct Fe sites corresponding to two local oxygen coordinations, and more significantly the spectra at 4.2 K for specimens with x≥0.03 show that the Fe moments are magnetically ordered, leading to the coexistence of superconductivity and magnetism.