Measurements of the critical magnetic field slope near the superconducting transition temperature Tc are reported for samples of and (Nbo.99Zro.ol)l-xGex for 0.15<-x<-0.25. The samples investigated were produced by trisputtering onto heated polycrystalline alumina substrates. The critical magnetic field slope near Tc for substituted samples is comparable to that of Nb3Ge alone. The highest T~ values, the highest resistance ratios, and the narrowest transitions, however, occur for samples with excess transition metal component.
We have previously reported the variation in the parallel critical field slopes dHez/dT near the zero-field, superconducting transition temperature Tc for (Nbo.99Ti0.01)l-xGex and (Nb0.99Zr0.ol)l_xGex. 1-3 The slopes previously reported were calculated using the onset transition temperature (the temperature that shows a change in slope from the normal state resistance versus temperature variation). The transition widths for these systems vary from -2 K at zero field to 4-6 K at 10 T. The slow variation of the resistance at the onset significantly contributes to the problems of determining the onset temperature. In Figs. 1-3 we present data to further characterize the variation of dHe2/dT near Tc in parallel field. The variation of dHc2/dT is given for five points along the superconducting transition: (1) the onset, (2) R =0.9RN, (3) R =0.5RN (midpoint), (4), R =0.1RN, (5) R =0 (zero electrical resistance), where RN is normal state electrical resistance.