By using photoemission spectroscopy we explore the modifications of $\mathrm{Mo}$ core levels upon electron filling the conduction band in the half-metallic ferromagnetic ${\mathrm{Sr}}_{2-x}{\mathrm{La}}_x{\mathrm{FeMoO}}_6\left(x=0\mathrm{to}0.6\right)$ oxides. The $3d$-core level $\mathrm{Mo}$ spectra of undoped $\left(x=0\right)$ samples reveal the presence of ${\mathrm{Mo}}^{6+}:{\mathrm{Mo}}^{5+}$ states in its ground state. Upon $\mathrm{La}$ doping, it is found that the $3d_{5∕2}–3d_{3∕2}{\mathrm{Mo}}^{5+}$ doublet progressively emerges and grows in intensity. It is interpreted as a signature of the electron injection into $\mathrm{Mo}$-based orbitals. The observation of distinguishable ${\mathrm{Mo}}^{6+}:{\mathrm{Mo}}^{5+}$ 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 $\mathrm{Mo}$ atoms and electronic phase separations.

• Received 9 January 2004

DOI:https://doi.org/10.1103/PhysRevB.70.054423