Behavior of Type II Superconductors in Very High Fields

Abstract

In some preliminary papers¹ we have reported on measurements carried out on some type II superconductors up to very high fields. In the meantime more measurements have been done, and the results on NbN have been published in detail². The details on critical data of A 15 (ß W) compounds are to be published ^3,4. From these data the critical field curves for some compounds are given in Fig. 1. The critical fields up to 150 kOe have been measured directly, but the higher critical fields at 4.2 ^OK for the ß-W compounds have been determined by extrapolation of the quenching curves to currents as low as 5 mA. The quenching curves for V₃Si and V₃Ga with various conditions of preparation are given as examples in Fig. 2 and 3 respectively. The experimental values of the upper critical field H_c2 (4.2) at 4.2 K and the extrapolated values of the upper critical field H_c2(O) at zero temperature are listed in Table 1. All measurements have been done at the MIT Francis Bitter National Magnet Laboratory, Cambridge, Mass., USA, using Bitter type solenoids for the generation of the high fields.