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

Electron spin resonance (ESR) experiments in the paramagnetic phase of ${\mathrm{R}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{B}}_{\mathrm{x}}$ ${\mathrm{MnO}}_{3+\mathrm{\delta }}$n(R=La,Pr; B=Ca,Sr) show, for 1.1 ${\mathrm{T}}_{\mathrm{C}}$≲T≲${2\mathrm{T}}_{\mathrm{C}}$, a linear T increase of the resonance linewidth, ΔH, in powders, ceramic pellets, and single crystals. Above ∼${2\mathrm{T}}_{\mathrm{C}}$ a slowdown in the T increase of ΔH 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 ∼${2\mathrm{T}}_{\mathrm{C}}$. A large T dependence of the resonance intensity above ${\mathrm{T}}_{\mathrm{C}}$ was found in all the samples studied, suggesting the existence of spin clusters in these compounds over a wide range of temperature.