Nonlinear susceptibilities of a weakly disordered uniaxial ferromagnet in the critical region

For a weakly disordered three-dimensional Ising model in the critical region, the sixth-order effective coupling constant and the fourth-and sixth-order nonlinear susceptibilities are determined. The values of these quantities are found to differ radically (by a factor of 1.5−3) from the corresponding values in a pure ferromagnet, and their measurement is suggested for the identification of the critical behavior of impure systems.