Polaron-mediated spin correlations in metallic and insulating La$_{1-x}A_{x}$MnO$_{3}$ ($A$=Ca, Sr, or Ba)

TL;DR

This study uses neutron spectroscopy to investigate short-range spin correlations and polaron effects in La$_{1-x}A_{x}$MnO$_{3}$, revealing magnetic scattering linked to polarons in both metallic and insulating phases.

Contribution

It introduces a simple hopping model to explain magnetic scattering and connects it to polaron behavior in manganite materials, across different electronic ground states.

Findings

Short-range spin correlations observed near phase transition.

Magnetic scattering ridges aligned along [100] directions.

Temperature-dependent diffuse scattering linked to polarons.

Abstract

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$_{3}$, 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 physics 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 structural scattering arising from individual polarons.