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

摘要: We have performed electron spin resonance (ESR) and dc susceptibility measurements in Mn perovskites up to 1000 K. Assuming an effective Heisenberg-like interaction for ${\mathrm{Mn}}^{3+}\mathrm{\ensuremath{-}}{\mathrm{Mn}}^{4+}$ pairs, the susceptibility, ${\ensuremath{\chi}}_{\mathrm{dc}}(T),$ is well described paramagnetic regime by constant coupling approximation. Absolute determination of ESR intensity indicates that all spins contribute line temperature range studied. The linewidth can be $\ensuremath{\Delta}{H}_{\mathrm{pp}}(T)=\ensuremath{\Delta}{H}_{\mathrm{pp}}(\ensuremath{\infty})[C/T{\ensuremath{\chi}}_{\mathrm{dc}}(T)],$ thus presenting a universal behavior scale normalized ${T}_{c}.$ A single relaxation mechanism, related spin-only interactions, explains $T$ dependence $\ensuremath{\Delta}{H}_{\mathrm{pp}}(T)$ compounds studied: ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3},$ ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3},$ ${\mathrm{Pr}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3},$ ${\mathrm{La}}_{0.67}{\mathrm{Pb}}_{0.33}{\mathrm{MnO}}_{3}.$ reflect progressive importance magnetic clustering below $\ensuremath{\approx}{2T}_{c}.$