Thermodynamic and Transport Properties of Superconducting ${\mathrm{Mg}}^{10}{B}_2$

Transport and thermodynamic properties of a sintered pellet of the newly discovered ${\mathrm{MgB}}_2$ superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, $H_{c2\mathrm{}}$, with magnetization data giving ${\mathrm{dH}}_{c2\mathrm{}}/dT=0.44\mathrm{}\mathrm{T}/\mathrm{K}$ at the transition temperature of $T_c=40.2\mathrm{}\mathrm{K}$. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of ${\mathrm{dH}}_c/\mathrm{dT}$ at $T_c$ is estimated to be about $12\mathrm{mT}/\mathrm{K}$, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter $\kappa \sim 26$. Estimates of the critical supercurrent density, $J_c$, using hysteresis loops and the Bean model, give critical current densities on the order of ${10}^5\mathrm{A}/{\mathrm{cm}}^2$. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like ${\mathrm{Nb}}_3\mathrm{Sn}$.