Temperature dependence of the ESR linewidth in the paramagnetic phase (T>T-C) of R(1-x)B(x)MnO(3+delta) (R=La,Pr; B=Ca,Sr)

Electron spin resonance (ESR) experiments in the paramagnetic phase of R(1-x)B(x)MnO(3+delta) (R=La,Pr; B=Ca,Sr) show, for 1.1 T-C less than or similar to T less than or similar to 2T(C), a linear T increase of the resonance linewidth, Delta H, in powders, ceramic pellets, and single crystals. Above similar to 2T(C) a slowdown in the T increase of Delta H is observed. The data resemble the results found in other ferromagnetic insulators where the spin-lattice relaxation involves a single-phonon process. We find that the one-phonon process may account for the linear T dependence of the linewidth observed up to similar to 2T(C). A large T dependence of the resonance intensity above T-C was found in all the samples studied, suggesting the existence of spin clusters in these compounds over a wide range of temperature.