Magnetic Properties of HTSC with a Weak Interlayer Coupling

Magnetic properties of layered high temperature superconductors with a weak interlayer coupling in the region of the critical fluctuations are investigated in the framework of the Ginzburg--Landau approach. The sample magnetization is calculated within a perturbative approach to the second order in the interlayer coupling constant. The first order correction can be incorporated into the non-interacting expression for the magnetization with the corresponding shift of the critical temperature. Only the second order contribution modifies the thermodynamics, leading to violation of the one-parameter 2D scaling low and to disappearance of the magnetization crossing point.