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 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 with the enhanced magnetotransport properties because of an additional hopping mechanism trough interfiling Mn(2+) ions. Such a scenario has been theoretically confirmed by calculations within the effective single-band model. The use of Mn(2+) 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.