Magnetic Orientation of Superconductors With Layered Crystal Structures

Tri-axial orientation of twin-free powder of Y₂Ba₄Cu₇O_15-δ (Y247) and uni-axial orientation of various FeAs-based compounds were attempted using modulated rotating and rotating magnetic fields, respectively. Tri-axial orientation with high degrees of inplane and c -axis orientation of Y247 was achieved under magnetic fields above 5 T, while magnetic fields at which reduction of the degrees began were different. We found from these crossover fields that quantitative magnetic anisotropy could be obtained. This determination method is particularly useful in that single crystalline samples are not required. From the magnetic orientation using the rotating field, all the obtained FeAs-based compounds showed a hard axis of magnetization parallel to the c-axis direction. On the other hand, the degrees of c-axis orientation were dependant on the types of ions in the blocking layers, and almost complete c-axis orientation was achieved for the compounds with transition-metal ions containing 3d electrons. Magnetic orientation using powder samples is a strong tool for the clarification of physical properties of Cooper pairs and critical current properties in FeAs-based superconductors.