Critical magnetic field of disordered Zr-Cu alloys: density of states and spin-orbit scattering time

The critical magnetic field {ital H}{sub {ital c}2} is measured for disordered Zr{sub {ital x}}Cu{sub 1{minus}{ital x}} for 0.36{lt}{ital x}{lt}0.65 in magnetic fields up to 3.5 T and temperatures down to 30 mK. Werthamer-Helfand-Hohenberg theory is found to describe the data well. The density of states {ital N}(0) and the spin-orbit relaxation time {tau}{sub so} are determined by fitting to the whole critical-field curve. We investigate how accurately these parameters can be obtained from critical-field measurements. {tau}{sub so}{sup {minus}1} is found to depend weakly on the Zr ionic mass. It is suggested that accurate critical-field data can give supplementing information in the study of weak localization and interaction effects. Evidence is found for some enhancement of {ital N}(0) obtained from the critical field as compared to results from the specific heat, thus confirming an earlier conjecture by Poon. Comparison with several published results suggests that this enhancement is small and only about 5--10 %.