“Mixed” state in type II ferromagnetic superconductor

We have studied a ferromagnetic superconductor having both a magnetic domain structure of the Kittel-type and a laminar structure of the normal regions. Our phenomenological approach is a combination of Ginzburg-Landau theory for superconductivity and the microscopic theory of ferromagnetism. Calculations of the thermodynamical potential and a comparison with Meissner and normal states offer the possibility to predict conditions for the crystal thickness and/or the absolute value of the magnetization vector at which the “mixed” state can exist.