Evidence for a distributed ferromagnetic transition in (La,Ca)MnO3

We report new zero-field μSR measurements in ferromagnetic (FM) (La,Ca)MnO3 which are consistent with two spatially separated regions in close proximity possessing very different Mn-ion spin dynamics. We present a picture in which one region corresponds to an extended spin polaron which displays a peak in the relaxation rate near the Curie temperature TC and an increasing volume fraction below TC. The second region possesses slower fluctuating spins and a decreasing volume fraction below TC. These data suggest a microscopically inhomogeneous FM phase transition resulting from the overlap of spin polarons.