Critical dynamics of an impurity spin in the Heisenberg ferromagnet below $T_C$

The results of an earlier paper of the authors are used to analyze the isothermal Green's functions of the magnetic moment of an impurity or nucleus in a Heisenberg ferromagnet at $T\lesssim T_C$. An investigation is made into the possible occurrence of a dip in the magnetic resonance line near the absorption maximum due to the interaction of the impurity spin with critical spin waves in the ferromagnet.