Boundaries of the critical state stability in a hard superconductor Nb3Al in the H–T plane

The instability of the critical state in a type-II superconductor Nb3Al is studied for the first time for simultaneous consideration of real dependences of thermal and conductive properties of the material on temperature T and magnetic field H-e. To do this the dependences of specific heat C(T,H), magnetization M(T,H-e) and magnetostriction Delta L(T,H-e) of the superconductor were investigated experimentally in a strong magnetic field (up to 12 T). The gap width, the coefficient of the linear term, which determines the electronic contribution to the specific heat, the Debye temperature, and other parameters were found using experimental data on the heat capacity in a wide range of temperatures and magnetic fields H-c1 <= H-e <= H-c2. From experimental studies of magnetization the dependences of the critical current of the superconductor, J(c)(T,H-e), were reconstructed. The hysteresis loops of magnetization and magnetostriction were calculated using experimental data for temperature and field dependences of the thermal and conductive properties. (C) 2013 AIP Publishing LLC.