Evidence for O2p Hole-Driven Conductivity in La1–x Srx MnO3 (0 ≤ x ≤ 0.7) and La0.7 Sr0.3 MnOz Thin Films

Oxygen K -edge electron-energy-loss spectra have been measured for La 1– x Sr x MnO 3 (0 ≤ x ≤ 0.7) and La 0.7 Sr 0.3 MnO z thin films as a function of x and z . The spectra show a prepeak at the Fermi level, corresponding to transitions to empty states in the O 2p band, at the threshold of the K edge around 529 eV. This prepeak systematically increases with an increase in conductivity through divalent doping ( x ) or oxygen content ( z ). This confirms that these materials are charge-transfer-type oxides with carriers having significant oxygen 2 p hole character. We argue that, the double exchange mechanism has to include the role of oxygen hole density to satisfactorily describe their transport properties.