Spin-glass transition in a La-doped Sr₂MnWO₆ double perovskite

Polycrystalline Sr₂-xLa_xMnWO₆ (x=0.25 and 0.5) materials have been prepared by a traditional solid state sintering method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature dependent NPD data shows that the compounds crystallize in monoclinic symmetry (space group P2₁/n). The unit cell volume decreases with increasing La³⁺ concentration at the A site. The crystal structure contains alternating MnO₆ and WO₆ octahedra, considerably tilted due to the relative small size of the cations that occupy the A sublattice of the perovskite. ac and dc magnetization measurements show a destruction of the low temperature antiferromagnetic phase by electron doping through substitution of Sr²⁺ for La³⁺. The electron doping creates a mixed tungsten valence (W⁶⁺/W⁵⁺) resulting in a low temperature spin-glass state.