Promising critical current density characteristics of Ag-sheathed (Sr,Na)Fe₂As₂ tape

Abstract

We report the fabrication of (Sr,Na)Fe2As2 superconducting tapes by the powder-in-tube technique and their characteristics, including the transport critical current density Jc at 4.2 K up to 140 kOe, the magnetic Jc estimated from magnetic hysteresis curves, magneto-optical (MO) images, and scanning electron microscopy images. In a tape sintered at 875 °C for 1 h, the transport Jc reaches 26 kA/cm2 at 4.2 K and 100 kOe for a field perpendicular to the tape surface. When the field is parallel to the tape surface, the magnetic Jc exceeds the practical level of 100 kA/cm2 at 4.2 K below 25 kOe. Analysis of the MO images reveals clear current discontinuity lines in the core, indicating that the current flows homogeneously and the connections between grains are strong in the core.