Superconducting Properties of Technetium

Abstract

Isothermal magnetization measurements are reported for technetium in the superconducting state from 1.5\ifmmode^\circ\else\textdegree\fi{}K to the transition temperature after various stages of heat treatment up to 2000\ifmmode^\circ\else\textdegree\fi{}C. The purer sample studied ($\ensuremath{\Gamma}=120$, where $\ensuremath{\Gamma}$ is the ratio of resistance at 295\ifmmode^\circ\else\textdegree\fi{}K to the resistance at 9\ifmmode^\circ\else\textdegree\fi{}K) was found to have a transition temperature of 7.73\ifmmode\pm\else\textpm\fi{}0.02\ifmmode^\circ\else\textdegree\fi{}K, and was destroyed in an early attempt at annealing, while the second sample ($\ensuremath{\Gamma}=97$), which had a transition temperature of 7.77\ifmmode\pm\else\textpm\fi{}0.02\ifmmode^\circ\else\textdegree\fi{}K, was studied more thoroughly. The magnetic behavior of this material is characteristic of a type-II superconductor, and the experimental temperature dependence of ${H}_{c2}$, 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\ifmmode^\circ\else\textdegree\fi{}C heat treatment, lead to an extrapolated value of ${H}_{c}(0)$ =1410 Oe, and a Ginzburg-Landau parameter of ${\ensuremath{\kappa}}_{1}(1)=0.92$. The data suggest that technetium is a weak-coupling superconductor of the BCS type, and the results are examined for self-consistency.