Phase transitions for MgB2 granular BCS - superconductor in weak magnetic fields

For the purpose of plotting the H-T diagram for MgB
₂
granular superconductors, the behavior of electrical resistivity-versus-temperature dependences were studied at ~ 35 to ~ 45K in external magnetic fields with magnetic field strengths H
_ext
up to ~ 2kOe. The effect of increasing the superconductivity transition width ΔT
_c
at increased H
_ext
has been revealed. A model has been developed for superconductivity transitions in a two-level system. The data obtained allowed establishing the existence of a weak links system in MgB
₂
granular superconductors.