Evidence of magnetization-dependent polaron formation in La$_{1-x}A_x$MnO$_3$, $A$=Ca, Pb

TL;DR

This study uses X-ray absorption measurements to investigate how magnetization influences polaron formation in La$_{1-x}A_x$MnO$_3$ compounds, revealing a link between magnetic order and local lattice distortions.

Contribution

It provides experimental evidence that magnetization affects polaron formation in manganites, highlighting the role of magnetic order in local lattice distortions.

Findings

Debye-Waller factor increases near $T_c$ in MI samples

Non-thermal disorder aligns with oxygen atom directions

Magnetization delocalizes small polarons

Abstract

X-ray-absorption fine-structure measurements at the Mn $K$-edge as a function of temperature were performed on samples of La$_{1-x}$Ca$_x$MnO$_3$ and La$_{0.67}$Pb$_{0.33}$MnO$_3$. All samples have a metal-insulator (MI) transition near the ferromagnetic transition, except the Ca$_{0.5}$ sample, which does not have a MI transition. Near $T_c$ for the MI samples, the Debye-Waller $\sigma^2$ for the Mn-O atom-pair increases rapidly with temperature. This non-thermal disorder is mostly along the direction of the neighboring oxygens. These results strongly suggest small polarons which are delocalized by a finite magnetization.