Flux-pinning behavior and the interlayer coupling of the superconductor

Previously the compound of (Formula presented) was believed to exhibit an enhanced flux-pinning behavior compared to the pristine (Formula presented) As candidates for its origin, possible extended defects of a superlattice in the (Formula presented) direction or a strong coupling deduced from a reduced distance between (Formula presented) planes have been proposed. To clarify these, we extensively measured the magnetization of the (Formula presented)-axis aligned grains of this compound. Contrary to previous belief, the irreversibility line and magnetic hysteresis show reduced pinning properties. From the analysis of the reversible magnetizations based on the vortex fluctuation model, the high-field scaling analysis, and the Hao-Clem model, the interlayer coupling was also confirmed to be weak. The proposed extended defects seem not to be effective in pinning vortices in (Formula presented).