Evolution of structure and magnetic properties in electron-doped double perovskites, Sr_2-xLa_xMnWO₆ (0≤x≤1)

Powder neutron and X-ray diffraction studies show that the double perovskites in the region 0≤x≤1 exhibit two crystallographic modifications at room temperature: monoclinic P21/n and tetragonal I4/m, with a boundary at 0.75<x<0.9. Magnetic susceptibility measurements indicate that for x=0 and 0.5 Sr_2-xLa_xMnWO₆ orders antiferromagnetically (AFM) at 15 and 25 K, respectively, for 0.75≤x<1.0, a contribution of weak ferromagnetism (FM), probably due to canted-AFM order, increases with increasing x. The end point compound SrLaMnWO₆ shows the strongest FM cluster effect; however, no clear evidence of magnetic order is discernable down to 4.2 K. X-ray absorption spectroscopy (XAS) confirms Mn ²⁺ and mixed-valent W^6+/5+ formal oxidation states in Sr_2-xLa_xMnWO₆.