Isothermal magnetization data were obtained for an annealed single crystal of vanadium (resistivity ratio p273K/p4K --450) in prolate spheroidal form in the temperature interval from T =1.4K to T~(=5. 43 K), which was measured to be 5.43 +0. 02 K. To minimize surface pinning and increase the reversibility of the bulk magnetization, the sample surface was subjected to an oxidation treatment. Values of the thermodynamic critical field H, (t) determined from the data are in good accord with ihe earlier results of Radebaugh and Keesom, and the Ginzburg-Landau parameter was deduced from the measurements to be y(1) =0.85+0.02. In the limit of infinite electronic mean free path it is found that f(;p=0 82 for this sample. The temperature variations of K f (t) K2(t), and the parameter 0* (t) = H~2(t) /( -d&,2/dt) t & are discussed and compared with previous work. The results tend to confirm the importance of Fermi-surface anisotropy effects in type-II superconductors in the clean limit.

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Isothermal magnetization measurements are reported for technetium in the superconducting state from 1.5°K to the transition temperature after various stages of heat treatment up to 2000°C. The purer sample studied (r = 120, where r is the ratio of resistance at 295°K to the resistance at 9°K) was found to have a transition temperature of 7.73±0.02°K, and was destroyed in an early attempt at annealing, while the second sample (r = 97), which had a transition temperature of 7.77±0.02°K, was studied more thoroughly. The magnetic behavior of this material is characteristic of a type-II superconductor, and the experimental temperature dependence of H C 2, the upper critical field, is compared with existing theories. Upper limits to the thermodynamic critical field H c (t), which have been obtained by integrating under the nonreversible magnetization curves observed after the 2000°C heat treatment, lead to an extrapolated value of H c (0) = 1410 Oe, and a Ginzburg-Landau parameter of KI(1) =0.92. The data suggest that technetium is a weakcoupling superconductor of the BCS type, and the results are examined for self-consistency.