Some Properties of Superconductors below 1°K. III. Zr, Hf, Cd, and Ti

Using techniques for the measurement of the magnetic threshold curves of superconductors below 1°K previously employed, investigations have been made on cadmium, zirconium, hafnium, and titanium, both before and after heat treatment. It was found that, in zirconium and hafnium, the magnetic superconducting properties were profoundly affected by heat treatment and that only after suitable annealing did these properties approach those of an ideal superconductor. The results for the annealed metals were as follows: the transition temperature, $T_c$ in zero magnetic field was 0.602°K for cadmium, 0.546°K for zirconium, 0.374°K for hafnium, 0.558°K for titanium and the slope of the magnetic threshold curves at $T=T_c$ in gauss/degree was 112 for cadmium, 170 for zirconium, 230 for hafnium, and 450 for titanium. The magnetic threshold curves for cadmium and zirconium were parabolic with $H_0=33.8\mathrm{}$ gauss for cadmium and 46.4 gauss for zirconium. The thermodynamically computed specific heat of the normal electrons was $1.54\times {10}^{-4\mathrm{}}T$ cal/mole-deg for cadmium and $3.92\times {10}^{-4\mathrm{}}T$ mole-deg for zirconium. No thermodynamic computations were made for hafnium and titanium owing to the irreversibility of their superconducting transitions.