Ferromagnetic Ordering and Unusual Magnetic Ion Dynamics in ${\mathrm{La}}_{0.67}$${\mathrm{Ca}}_{0.33}$Mn${\mathrm{O}}_3$

Zero-field muon spin relaxation and resistivity experiments on ${\mathrm{La}}_{0.67}$ ${\mathrm{Ca}}_{0.33}$Mn${\mathrm{O}}_3$ powder show that the sublattice magnetization ${\nu }_{\mu }\mathrm{}\left(T\right)\mathrm{}$ is well described for $T\le T_c$ by ${(1-\frac{T}{T_c})}^{\beta }$, where $\beta =0.345\mathrm{}\pm 0.015$, characteristic of a second-order phase transition for a 3D spin system, and the ferromagnetic transition temperature ($T_c=274\mathrm{}$ K) and resistivity peak temperature coincide to within 1 K. Below $T_C{\nu }_{\mu }$ and the zero-field resistivity $\rho$ are correlated, with ${\nu }_{\mu }\propto -\ln \rho$. Unusual relaxational dynamics suggest spatially inhomogeneous Mn-ion correlation times. These results are discussed in terms of the possible effects of polarons on the spin and charge dynamics.