Nonlinear Magnetization in Superconductors with s + d Ordering.

The nonlinear magnetization in the Meissner regime is considered within the Ginzburg-Landau theoretical framework. A calculational method in the case of conventional superconductors (one order parameter) is developed and this method is extended for the case of two order parameters (s+d mixing). In the mean field analysis, corrections to the penetration depth are of order H-02 where H-0 is the applied field. The anisotropy in the penetration depth is calculated and the temperature dependence of the magnetization is extracted. Signatures of the different ordering possibilities are derived. We discuss the relevant experimental results in the light of these calculations.