Effect of Sn, Nb, and La substitution on superconductivity and magnetic order in RuSr2RCu2O8 (R=Eu,Gd)

Abstract

We report the results from a resistance, and magnetization study on Ru1−xAxSr2−zBzRCu2O8 (A=Sn,Nb,B=La,R=Eu,Gd) where the parent compound has previously been reported to display superconductivity and predominately low field antiferromagnetic order. We show that, contrary to a study on Ru1−xSnxSr2GdCu2O8, there is no significant change in the superconducting transition temperature when Sn is substituted for Ru, implying that there is no significant Sn-induced charge transfer to the CuO2 planes. Furthermore, increasing the Sn concentration has the effect of increasing the temperature where zero resistance and the onset of bulk ac diamagnetic shielding occurs, which we interpret in terms of a decreasing ferromagnetic component leading to an increase in the temperature where the spontaneous vortex phase occurs. Contrary to previous studies on the pure compounds, we find an initial negative dM/dB at low temperatures in magnetically ordered Ru1−xSnxSr2RCu2O8 for Sn concentrations at, and greater than, 0.1. The substitution of Ru by nuclei that have a larger (Nb5+) or smaller (Sn4+) valence results in a similar decrease in the magnetic ordering temperature and an increase in the average Ru valence. La substitution for Sr causes charge transfer to the CuO2 planes and an increase in the magnetic ordering temperature that is not expected.

Source-reported materials — not catalogue approval

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