Upper critical fields and superconducting transition temperatures of some zirconium-base amorphous transition-metal alloys

Superconducting upper critical fields $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$, transition temperatures $T_c$ and normal-state electrical resistivities ${\rho }_n$ have been measured in the amorphous transition-metal alloy series ${\mathrm{Zr}}_{1-x}{\mathrm{Co}}_x$, ${\mathrm{Zr}}_{1-x}{\mathrm{Ni}}_x$, ${\left({\mathrm{Zr}}_{1-x}{\mathrm{Ti}}_x\right)}_{0.78}{\mathrm{Ni}}_{0.22}$, and ${\left({\mathrm{Zr}}_{1-x}{\mathrm{Nb}}_x\right)}_{0.78}{\mathrm{Ni}}_{0.22}$. Structural integrity of these melt-spun alloys is indicated by x-ray, density, bend-ductility, normal-state electrical resistivity, superconducting transition width, and mixed-state flux-pinning measurements. The specimens display $T_c=2.1-3.8\mathrm{}$ K, ${\rho }_n=159-190\mathrm{}$ μΩ cm, and $\left|{\left(\frac{d{H}_{c2\mathrm{}}}{\mathrm{dT}}\right)}_{T_c}\right|=28-36\mathrm{}$ kG/K. These imply electron mean free paths $l\approx 2-6$ Å, zero-temperature Ginzburg-Landau coherence distances ${\xi }_{G0\mathrm{}}\approx 50-70$ Å, penetration depths ${\lambda }_{G0\mathrm{}}\approx \mathrm{}(7-10)\mathrm{}\times {10}^3$ Å, and extremely high dirtiness parameters $\frac{{\xi }_0}{l}\approx 300-1300$. All alloys display $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ curves with negative curvature and (with two exceptions) fair agreement with the standard dirty-limit theory of Werthamer, Helfand, Hohenberg, and Maki (WHHM) for physically reasonable values of spin-orbit-coupling induced, electron-spin-flip scattering time ${\tau }_{\mathrm{so}}$. This is in contrast to the anomalously elevated $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ behavior which is nearly linear in $T$ that is observed by some, and the unphysically low-${\tau }_{\mathrm{so}}$ fits to WHHM theory obtained by others, for various amorphous alloys. Current ideas that such anomalies may be due to alloy inhomogeneity are supported by present results on two specimens for which relatively low-