Critical dynamics of an impurity spin in a perromagnet above $T_C$

An approximate expression is obtained for the isothermal Green's function for the magnetic moment of an interstitial impurity in a ferromagnet in the upper kinetic region $(T\gtrsim T_C)$. This expression is used to analyze the behavior of the Green's function in the time representation in three temperature intervals near $T_C$. It is shown that the asymptotic behaviors of the Green's function at large times contain weakly damped power-law “tails” of two types, these being, respectively, the contributions of the hydrodynamic and critical spin modes of the ferromagnet. It is found that in the two regions closest to $T_C$ there does not exist a purely relaxation regime in the behavior of the considered Green's function.