Valence and spin states, and the metal-insulator transition in ferromagnetic La2-xSrxMnNiO6 (x=0,0.2)

Electronic structures of a ferromagnetic insulator La2MnNiO6 and Sr-doped La1.8Sr0.2MnNiO6 have been investigated by employing soft x-ray synchrotron-radiation spectroscopies, first-principles band-structure calculations, and ligand-field multiplet calculations. Our study provides evidence that La2MnNiO6 has the [high-spin (HS) Mn4+-(3)A(2) Ni2+] configuration while La1.8Sr0.2MnNiO6 has [HS Mn4+-(3)A(2) Ni2+ low-spin Ni3+]. It is directly observed that the spin moments of Mn and Ni ions are coupled ferromagnetically. The metallic spectral weight is observed for x=0.2 in O 1s x-ray absorption spectroscopy, which is consistent with the half-metallic ground state predicted by band-structure calculations.