Resonance line shape in a magnetically diluted system of an arbitrary dimensionality

The third ($\propto C^2$) term in the concentration expansion of free induction decay is calculated for a magnetically diluted system of an arbitrary integer dimensionality $d\leq3$ and for different values of parameter a characterizing the relative intensity of flip-flop processes. The concentration expansion was used to generalize, in a natural way, the Anderson-Weiss-Kubo theory that was originally developed to describe magnetic resonance in ordered systems in terms of the second and fourth moments. The results are compared with recent absorption measurements in quasi-two-dimensional media. The possibility of describing the exchange narrowing is discussed.