Probing Mo core valence on Sr2FeMoO6 half-metallic ferromagnets and their electron-doped derivative compounds by photoelectron spectroscopy -: art. no. 054423

By using photoemission spectroscopy we explore the modifications of Mo core levels upon electron filling the conduction band in the half-metallic ferromagnetic Sr2-xLaxFeMoO6 (x=0 to 0.6) oxides. The 3d-core level Mo spectra of undoped (x=0) samples reveal the presence of Mo6+:Mo5+ states in its ground state. Upon La doping, it is found that the 3d(5/2)-3d(3/2)Mo(5+) doublet progressively emerges and grows in intensity. It is interpreted as a signature of the electron injection into Mo-based orbitals. The observation of distinguishable Mo6+:Mo5+ states may have severe implications on current understanding of the microscopic origin of the ferromagnetic coupling in these oxides and on suggestions of a negative effective Coulomb interaction at Mo atoms and electronic phase separations.