Thermodynamic and Transport Properties of Superconducting Mg¹⁰B₂

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB₂ 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, with magnetization data giving dH_c2/dT  =  0.44 T/K at the transition temperature of T_c  =  40.2 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 dH_c/dT at T_c is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter κ∼26. Estimates of the critical supercurrent density, J_c, using hysteresis loops and the Bean model, give critical current densities on the order of 10⁵ A/cm². Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb₃Sn.