High-Field Superconductivity of Carbides

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°K. ${\mathrm{Mo}}_3$ ${\mathrm{Al}}_2$C is the only known superconductor with the $\beta -\mathrm{M}\mathrm{n}$ crystal structure. From the available data the electronic specific-heat coefficient $\gamma$, the thermodynamic critical field $H_c$, the Ginzburg-Landau parameter $\kappa$, and the lower critical field $H_{c1\mathrm{}}$ were estimated at the experimental temperatures.