The Bloch-Hasegawa theory for the ESR of magnetic alloys is adapted and extended to spin glasses in the paramagnetic regime, that is, for temperatures T>TG, the cusp temperature. Negative residual widths, reduced thermal broadening, and a possible critical divergence of the residual width are all explained in terms of minor extensions of the standard theory.
Barnes, S. E., "ESR Relaxation in Spin Glasses" (1984). Physics Articles and Papers. 55.