Polaron-Mediated Spin Correlations in Metallic and Insulating La$_{1-x}A_{x}$MnO$_{3}$

Neutron spectroscopy measurements reveal short-range spin correlations near and above the ferromagnetic-paramagnetic phase transition in manganite materials of the form La$_{1-x}A_{x}$MnO$_{3}$ ($A$=Ca, Sr, or Ba), including samples with an insulating ground state as well as colossal magnetoresistive samples with a metallic ground state. Quasielastic magnetic scattering is revealed that forms clear ridges running along the [100]-type directions in momentum space. A simple model consisting of a conduction electron hopping between spin polarized Mn ions that becomes self-trapped after a few hops captures the essential aspects of this magnetic component of the scattering. We associate this scattering component with the magnetic part of diffuse polarons, as we observe a temperature dependence similar to that of the diffuse nuclear scattering arising from individual polarons.