The effect of titanium content on the pinning force in Nb44wt.%Ti to Nb62wt.%Ti

The authors have been studying high Ti alloys to establish whether they offer higher low-field J_c values than Nb46.5wt.%Ti and find that they do, with values, as high as 7500 A/mm ² at 2 T, 4.2K. They have established that the pinning centers are α-Ti precipitates for all alloys from Nb44wt.%Ti to Nb62wt.%Ti, but find a steady shift in the pinning curve peak to lower reduced fields at 4.2 K. Recently, it was shown that both ΔH _c and Δκ pinning can be recognized in Nb47wt.%Ti. Since T_c and H_c vary rapidly in the high Ti alloys, ΔH_c pinning should be proportionately stronger in the high Ti alloys, leading to a displacement of the peak in the pinning force curves to lower fields. The authors present pinning force data at 1.8 K and 4.2 K across the alloy range and find that while lower Ti alloys do exhibit b(1- b) behavior, the higher Ti alloys never realize b^1/2(1-b)² behavior