Influence of fluorine in magnetic properties of Hg-1223 high-temperature superconductors

Abstract

Bulk pure-phase samples of HgBa 2Ca 2Cu 3O y with high quality were prepared using a solid-state reaction with BaF 2 as a part of the starting material. X-ray diffraction data show that the crystal structure is nearly the same as for starting compounds without fluorine with a = 3.85 A ̊ and c = 15.85 A ̊ . The effect of fluorine in the starting material on the magnetic properties was studied by DC susceptibility and hysteresis-loop measurements, and our results revealed a remarkable enhancement of hysteretic magnetization in samples prepared using BaO/BaF 2. Fluorine in Hg-1223 also shows an effect similar to that of oxygenation, which increases T c onset of the as-synthesized samples to 133 K. The asymmetric magnetization-field data indicate the presence of a surface barrier, and the field dependence and time dependence of the magnetization data display an enhancement of hysteresis upon replacement of 10% of BaO by BaF 2 as a result of increased concentration of pinning centers without changing the nature of the individual pinning.