Influence of Spin Paramagnetism on Superconductivity

The Ginsburg-Landau equations are modified to include a magnetic permeability which varies with the order parameter $\psi$ according to the relation: $\mu ={\mu }_s{\psi }^2+{\mu }_n(1-{\psi }^2)$. The influence of this on the predicted behavior of a superconducting film in a tangential magnetic field is investigated theoretically. A new value is derived for the upper limit of the critical field for a bulk superconductor and a thin film.