We have measured the ratio $\frac{H_{c3\mathrm{}}}{H_{c2\mathrm{}}}$ for tin-rich Sn-In alloys and for indium-rich In-Bi alloys in the immediate vicinity of $T_c$. For the Sn-In system this ratio decreases as $T_c$ is approached. Similar behavior has been recently reported by Ostenson and Finnemore for pure Nb. The In-Bi alloys, however, show a marked increase in $\frac{H_{c3\mathrm{}}}{H_{c2\mathrm{}}}$ as the critical temperature is approached.

• Received 14 May 1969

DOI:https://doi.org/10.1103/PhysRev.187.766