Dependence of critical current density on microstructure in the SnMo6S8 Chevrel phase superconductor

Abstract

Microstructure and superconducting properties of hot isostatic pressed SnMo6S8 were systematically studied. Magnetization was measured in fields up to 30 T at 4.2–14 K. SnMo6S8 exhibits critical current densities limited by flux pinning, not by granularity. Samples exhibited Birr(T)∼Bc2(T), indicative of strong flux pinning. Pinning force curves contained two distinct peaks, indicating that at least two pinning mechanisms are active. The microstructure contained two types of defects which could pin flux: grain boundaries and planar intragranular defects. Lower-field pinning (B/Bc2≤0.3) was directly correlated to the grain boundary density. Higher-field pinning (B/Bc2≥0.5) appeared to be controlled by the intragranular pins. Compared to Nb3Sn, the grain sizes are large and the contribution from grain boundary pinning is small. Inhibiting grain growth through lower-temperature processing and increasing the density of intragranular defects both appear feasible means of further increasing Jc.