La₂MnVO₆ double perovskite: A structural, magnetic and X-ray absorption investigation

The synthesis, electron diffraction (ED), synchrotron X-ray and neutron structure, X-ray absorption spectroscopy (XAS) and magnetic property studies of La₂MnVO₆ double perovskite are described. Analysis of the synchrotron powder X-ray diffraction data for La₂MnVO₆ indicates a disordered arrangement of Mn and V at the B-site of the perovskite structure. Absence of super-lattice reflections in the ED patterns for La ₂MnVO₆ supports the disordered cation arrangement. Room temperature time-of-flight (TOF) neutron powder diffraction (NPD) data show no evidence of cation ordering, in corroboration with the ED and synchrotron studies (orthorhombic Pnma, a = 5.6097(3), b = 7.8837(5) and c = 5.5668(3) ; 295 K, NPD). A comparison of XAS analyses of La₂TVO₆ with T = Ni and Co shows T²⁺ formal oxidation state while the T = Mn material evidences a Mn³⁺ admixture into a dominantly Mn²⁺ ground state. V-K edge measurements manifest a mirror image behavior with a V ⁴⁺ state for T = Ni and Co with a V³⁺ admixture arising in the T = Mn material. The magnetic susceptibility data for La ₂MnVO₆ show ferromagnetic correlations; the observed effective moment, _eff (5.72 _B) is much smaller than the calculated moment (6.16 _B) based on the spin-only formula for Mn ²⁺ (d⁵, HS) /V⁴⁺ (d¹), supportive of the partly oxidized Mn and reduced V scenario (Mn³⁺/V³⁺).