Critical properties of a dense polycrystalline(Ba, K)Fe2As2 superconductor prepared by a combined process of melting and deformation

Abstract

We report the synthesis of a polycrystalline bulk(Ba, K)Fe2As2 superconductor by a combined process of melting and deformation. The samplehas fewer impurity phases and a higher density compared to samples preparedby a conventional sintering process. Magneto-resistance and magnetizationmeasurements were carried out on the sample in order to evaluate superconductingcritical properties. The temperature dependence of the upper critical field, − dHc2(T)/dT, is aslarge as ∼ 9 T K − 1, which corresponds to the value of a single crystal in a magnetic field parallel to thea–b plane. The temperature dependence of irreversibility fields, − dHirr(T)/dT, also has a steep slopeat about 10 K below Hc2(T), suggesting that (Ba, K)Fe2As2 superconductors have a good potential for magnetic applications at medium temperatures, likeMgB2.However, the magnetization hysteresis loop shows a very small dependence on sample size and the globalJc estimated isas low as ∼ 2 × 103 A cm − 2 at 5 K in applied magnetic fields, while the localJc estimated from the powdered sample is about two orders of magnitude higher. Thoseresults indicate that the current path is still largely limited in the bulk sample despite itshigh density, and a weak link at the grain boundary is the most plausible origin of thecurrent limitation in the bulk sample.