Magnetization and Re L-III-edge studies of (Hg,Re)Sr2CuO4+delta system

Abstract

Chemically stable nominal compositions of (Hg1-xRex)Sr2CuO4+delta (x = 0.05, 0.10, and 0.20), designated as (Hg, Re)-1201 phase,were synthesized at similar to920degreesC in partial vacuum. The samples with x = 0.05 and 0.10 are superconducting (SC) with T-c(onset) similar to40 and similar to54 K, respectively. On the other hand, for the composition with x = 0.20, the sample is nonsuperconducting down to 5 K. The sample with composition (Hg0.9Re0.1)Sr2CuO4+delta on cooling, below 10 K in dc-fteld of 4 kOe, shows a dramatic decrease (reversal) in diamagnetic signal. Such a reduction in diamagnetic response is also reflected by the sample's supercurrent induced magnetic hysteresis curve generated at 9 K. In the light of the available reports and our Re L-III-edge measurements, we attribute this effect to a field enhanced paramagnetic contribution probably arising mainly from mixed valent (6(+), 7(+) dominant) Re ions. The critical current density (J(c)), calculated using Bean's model, for (Hg0.9Re0.1)Sr2CuO4+delta is similar to6 x 10(3) A/cm(2) (4.5 K, 5 kOe).