High-Field Superconductivity of Carbides

Abstract

The high-magnetic-field properties of some refractory carbides were investigated at low temperatures. The upper critical fields for NbC, a solid solution of 40% NbC-60% TaC, and TaC are between 4.2 and 21.3 kG; MoC, ${\mathrm{Mo}}_{56}$${\mathrm{C}}_{44}$, and ${\mathrm{Mo}}_{60}$${\mathrm{C}}_{40}$+2% VC have upper critical fields between 80 and 120 kG; and ${\mathrm{Mo}}_{3}$${\mathrm{Al}}_{2}$C has an upper critical field of 156 kG at 1.2\ifmmode^\circ\else\textdegree\fi{}K. ${\mathrm{Mo}}_{3}$${\mathrm{Al}}_{2}$C is the only known superconductor with the $\ensuremath{\beta}\ensuremath{-}\mathrm{M}\mathrm{n}$ crystal structure. From the available data the electronic specific-heat coefficient $\ensuremath{\gamma}$, the thermodynamic critical field ${H}_{c}$, the Ginzburg-Landau parameter $\ensuremath{\kappa}$, and the lower critical field ${H}_{c1}$ were estimated at the experimental temperatures.