High-temperature spin dynamics in CMR manganites: ESR and magnetization

We have performed electron spin resonance (ESR) and de susceptibility measurements in Mn perovskites up to 1000 K. Assuming an effective Heisenberg-like interaction for Mn3+ - Mn4+ spin pairs, the de susceptibility, chi(dc)(T), is well described in the paramagnetic regime by the constant coupling approximation. Absolute determination of the ESR intensity indicates that all Mn spins contribute to the ESR line in the temperature range studied. The ESR linewidth can be described by Delta H-pp(T)= Delta H-pp(infinity) [C/T chi(dc)(T)], thus presenting a universal behavior in a temperature scale normalized to T-c. A single relaxation mechanism, related to spin-only interactions, explains the T dependence of Delta H-pp(T) for all the compounds studied: La0.67Ca0.33MnO3, La0.67Sr0.33MnO3, Pr0.67Sr0.33MnO3, and La0.67Pb0.33MnO3. The de susceptibility and the ESR linewidth and intensity all reflect the progressive importance of magnetic clustering below approximate to 2 T-c.