Multiple double-exchange mechanism by Mn2+ doping in manganite compounds

Double-exchange (DE) 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 Mn3+ and Mn4+ 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 Mn2+ ions, in La-deficient LaxMnO3-delta thin films. X-ray absorption spectroscopy demonstrated the relevant presence of Mn2+ ions, which is unambiguously proved to be substituted at La site by resonant inelastic x-ray scattering. Mn2+ is proved to be directly correlated with the enhanced magnetotransport properties because of an additional hopping mechanism trough interfiling Mn2+ ions. Such a scenario has been theoretically confirmed by calculations within the effective single-band model. The use of Mn2+ both as a doping element and an ion electronically involved in the conduction mechanism reveals an unconventional phenomenon in transport properties of manganites. More important, such a strategy might be also pursed in other strongly correlated materials.