Anomalous anisotropy of critical currents in (Sr, K)Fe₂As₂tapes

Abstract

We measured critical currents and irreversibility fields of Ag-sheath (Sr, K)Fe2As2 tapes at various temperatures, magnetic fields and magnetic field directions. The sample tapes were made by a powder-in-tube with a hot-press process in the final heat treatments. The inverse anisotropy in Jc in comparison with the effective mass anisotropy can be found in the hot-pressed (Sr, K)Fe2As2 tapes. We found that the broad c-axis peak in angular dependence of Jc appears in a low field region and it decreases with increasing field and temperature. In addition, the crossover of Jc anisotropy appears around 10 T at 4.2 K and the crossover field decreases with increasing temperature. It is considered that these unusual anisotropic Jc behaviors may be originated by the strong random pinning center which is larger than the coherence length,