Artificial pinning center Nb-Ti superconductors with alloyed Nb pins

A magnetic interaction has been proposed as the dominant fluxon-defect interaction in conventional and artificial pinning center (APC) Nb-Ti, emphasizing the proximity length (xi(N)) of the pinning center as the important parameter for optimizing the high field critical current density. We have characterized APC composites containing 25 vol.% of Nh pins alloyed with 7.5 wt.% Ta and 10 wt.% W to deliberately test the predictions of this model. We found that the bulk flux pinning force of the Nb10W-pin composite (xi(N)(Nb10W)similar to 32 nm) exhibited a magnetic field (H) and pin size (d(p)) dependency that is more consistent with conventionally processed Nb47Ti (xi(N)(alpha-Ti)<32 nm) than with existing pure Nb-pin APC composites (xi(N)(Nb)similar to 83 nm). The Nb7Ta-pin composite (xi(N) similar to 59 nm) had intermediate F-p(H,d(p)) behavior, thus qualitatively supporting the model.