  Recent measurements of fluctuation diamagnetism in high temperature
superconductors show distinct features above and below Tc, which can not be
explained by simple gaussian fluctuation theory. Self consistent calculation of
magnetization in layered high temperature superconductors, based on the
Ginzburg-Landau-Lawrence-Doniach model and including all Landau levels is
presented. The results agree well with the experimental data in wide region
around Tc, including both the vortex liquid below Tc and the normal state above
Tc. The gaussian fluctuation theory significantly over estimates the
diamagnetism for strong fluctuations. It is demonstrated that the intersection
point of magnetization curves appears in the region where the lowest Landau
level contribution dominates.
