Thermodynamic theory of a specific superconducting phase transition

The phase transition “type I to type II superconductivity” was investigated theoretically by thermodynamic methods in the framework of the GLAG formalism. The conditions of the forming of the vortex lattice structure were determined and the features of the transition described. It was shown that the order parameter becomes space dependent in a periodic way during the phase transition. The critical value of the GL parameter and the range of the wave number belonging to the magnetic vortices which appear at the transition were given.