Multiple double-exchange mechanism by Mn$^{2+}$-doping in manganite compounds

TL;DR

This paper uncovers a new double-exchange mechanism in manganites by doping with Mn$^{2+}$ ions, which enhances magneto-transport properties through an additional hopping pathway, a novel approach in strongly correlated materials.

Contribution

It introduces a novel doping strategy using Mn$^{2+}$ ions in manganites, revealing a new conduction mechanism and improving magnetic and transport properties.

Findings

Mn$^{2+}$ ions are incorporated at La sites in La$_{x}$MnO$_{3- ext{delta}}$ thin films.

The presence of Mn$^{2+}$ correlates with enhanced magneto-transport properties.

The new hopping mechanism via Mn$^{2+}$ ions is confirmed by theoretical calculations.

Abstract

Double-exchange mechanisms in RE$_{1-x}$AE$_{x}$MnO$_{3}$ manganites (where RE is a trivalent rare-earth ion and AE is a divalent alkali-earth ion) relies on the strong exchange interaction between two Mn$^{3+}$ and Mn$^{4+}$ ions through interfiling oxygen 2p states. Nevertheless, the role of RE and AE ions has ever been considered "silent" with respect to the DE conducting mechanisms. Here we show that a new path for DE-mechanism is indeed possible by partially replacing the RE-AE elements by Mn$^{2+}$-ions, in La-deficient La$_{x}$MnO$_{3-\delta}$ thin films. X-ray absorption spectroscopy demonstrated the relevant presence of Mn$^{2+}$ ions, which is unambiguously proved to be substituted at La-site by Resonant Inelastic X-ray Scattering. Mn$^{2+}$ is proved to be directly correlated to the enhanced magneto-transport properties because of an additional hopping mechanism trough interfiling Mn$^{2+}$-ions, theoretically confirmed by calculations within the effective single band model. The very idea to use Mn$^{2+}$ both as a doping element and an ions electronically involved in the conduction mechanism, has never been foreseen, revealing a new phenomena in transport properties of manganites. More important, such a strategy might be also pursed in other strongly correlated materials.