High‐field properties and scaling in CVD‐prepared Nb3Ge

The upper critical field Hc2 and the field‐dependent critical current density Jc(H) have been determined for high‐Tc Nb3Ge prepared by the chemical vapor deposition (CVD) process. Measurements were performed on short samples taken from long lengths (∼10 m) of Nb3Ge deposited under various conditions onto metallic substrates. Using the theory of Hohenberg and Werthamer for dirty type‐II superconductors, values of Hc2(0) were extrapolated from resistive measurements of Hc2 near Tc. Values of Hc2(0) ranged from 32.2 to 33.1 T, the highest upper critical field reported for bulk Nb3Ge. From measurements of Jc(H), pinning force densities Fp were calculated and compared to the Kramer model of flux pinning which predicts certain scaling laws for Fp. We have tested for these scaling laws and have found qualitative agreement with the model of Kramer. This represents the first demonstration of such scaling in bulk high‐Tc Nb3Ge. In addition, values of the flux line lattice shearing parameter Ks have been extracted f...