Shift of the flux-pinning force curve in Nb3Sn thin films with very fine grain size

Nb3Sn thin films were made by splitter deposition of Nh onto bronze substrates at various temperatures. Deposition at 660 degreesC produced a Nb3Sn reaction immediately, which resulted in films with 20-50 nm grains. The peak of F-p(H) for one of these films was at 0.35 to 0.38H*, higher than the field where the standard flux-shear curve peaks, 0.2H*. Deposition at 400 degreesC produced Nb films that were later reacted to form Nb3Sn films with 50-250 nln grains. These films also exhibited F-p(H) curves with peeks higher than 0.2H*, hut the shift was not as pronounced as for the rapidly formed films. The shift of the pinning forte cur ve to higher fields is discussed in terms of the grain she difference and a recent flux-pinning model. All of the films exhibited an expanded Nb3Sn lattice parameter and degraded superconducting properties, due to disorder and interstitial impurities.