Irreversibility temperatures ofNb3Sn and Nb-Ti

Abstract

For fine multifilamentary ${\mathrm{Nb}}_3$Sn and Nb-Ti wires, it was found that there exists a surprisingly large temperature region (e.g., ∼1 and 0.5 K at 2 T for a ${\mathrm{Nb}}_3$Sn and Nb-Ti wire, respectively) below the mean-field critical-magnetic-field line ${\mathit{H}}_{\mathit{c}2}$(T) where the magnetization is reversible during a cycle of warming and cooling. The magnetic-field dependence of the lower boundary of this temperature region, i.e., the irreversibility temperature ${\mathit{T}}_{\mathit{r}}$(H), was shown to follow theoretical predictions for flux-lattice melting based on an analysis of thermally induced flux-line fluctuations calculated with nonlocal lattice elasticity and the Lindemann melting criterion.