Effect of Temperature and of Substitutional Mo on the Magnetic Behavior of Superconducting Nb

The temperature and mean-free-path dependence of the magnetic properties of highly reversible samples of Nb and some of its alloys with Mo are compared with recent generalizations of the Ginzburg-Landau-Abrikosov-Gor'kov theory. The temperature dependence of ${\kappa }_1$ and ${\kappa }_2$ in pure Nb is much more rapid than the theoretical predictions, as in the measurements of Finnemore et al. The disparity between theory and experiment decreases with increasing Mo content. The temperature dependence of the lower critical field of pure Nb is in violent disagreement with theory, while at least qualitative agreement is found in the case of the alloy samples.