Superconductivity in magnetically ordered Ru1-xIr xSr2GdCu2O8 compounds

Abstract

We have performed a systematic study of the structural, transport, and magnetic properties of polycrystalline samples of the magnetic superconductors Ru1−xIrxSr2GdCu2O8; x = 0, 0.02, 0.05, 0.10, and 0.15. The samples were prepared by solid state reaction and sintered at 1060 • C for 72 h under O 2 flow. X-ray diffraction analysis shows that all samples are nearly single phase and that the lattice parameters are independent of Ir content. Transport properties measurements revealed that the Ru substitution by Ir results in a decrease of Tc,onset from ∼ 50 K (x = 0) to ∼ 30 K (x = 0.10). Further addition of Ir (x > 0.10) causes an evolution from metallic to nonmetallic behavior of ρ(T). We have also found that magnetic order develops in the undoped Ru-1212 materials near T M ∼ 130 K. This temperature decreases linearly with increasing Ir content at the rate of ∼ -1.6 K / Ir at.%, suggesting that Ir effectively substitutes Ru in the RuO planes. A subtle drop in ρ(T) is observed close to T M , probably due to the suppression of the spin-flip scattering. The magnetoresistivity measurements revealed that the temperature T c,zero , in which ρ(T) ∼ 0, decreases rapidly for low applied magnetic fields (H < 2 T), and that this drop becomes much less pronounced in higher magnetic fields (2 ≤ H ≤ 18 T). The appreciable broadening of ρ(T) curves at low magnetic fields is reminiscent of the behavior in high-T c materials showing granular behavior, as for example in Sm1.85Ce0.15CuO4−y.

Effect of Ir substitution in the ferromagnetic superconductor RuSr2GdCu2O8

“…15 The two-step synthesis minimizes the formation of the SrRuO 3 phase, yielding samples with better quality. 16 Initially, the Sr 2 GdRu 1−x Ir x O 6 (Sr-2116) precursor was prepared by mixing stoichiometric quantities of high purity Ru, Ir, SrCO 3 , and Gd 2 O 3 , grinding together and heating in air at 1250 • C for 12 h. Then, CuO was mixed to the Sr-2116 powders, ground together, pressed into pellets, and sintered at 1060…”