Valence electronic states related to Mn2+ ions at La0.7Sr0.3MnO3 surfaces characterized by resonant photoemission

Nonferromagnetic Mn2+ ions can be readily formed at the surface of half metallic La0.7Sr0.3MnO3 manganite as demonstrated by deoxygenating surface treatments. The 3d(5) contribution of these Mn2+ ions to the valence-band electronic structure has been characterized using Mn(2p) to 3d resonant photoemission measurements. The Mn2+ related 3d electrons were found to be stabilized by about 2 eV with respect to the mixed-valence 3d states, indicating their strong localization. Active participation of Mn2+ states in both spin and charge conductivity processes is therefore excluded. A two-channel picture, including independent Mn3+/Mn4+ and Mn2+ channels, emerges from detailed data analysis. Reversible Mn2+ formation and straightforward oxygen annealing effects point to a direct bonding between Mn2+ and oxygen vacancies that are most probably created at preexisting structural defects. The t(2g) and e(g) states of the mixed valence Mn3+/Mn4+ ions remain unaffected as the Mn2+ content increases, indicating a robust Mn3+/Mn4+ channel independent of structural defects.