The crystal structures and magnetic properties of Ba2LaRuO6 and Ca2LaRuO6

Profile analysis of high-resolution, powder neutron-diffraction data was used to refine the previously reported structures of the ordered, distorted perovskites Ba₂LaRuO₆ and Ca₂LaRuO₆. Low-temperature neutron diffraction experiments showed that, at 2K, the former is a Type IIIa antiferromagnet while the latter is Type I. Both compounds have an ordered magnetic moment of $\text{μ}{}_{\mathrm{<mtext>Ru</mtext>}}\text{? 1.95μ}{}_{\mathrm{<mtext>B</mtext>}}$ per Ru⁵⁺ ion. The Néel temperature of Ba₂LaRuO₆ was determined to be 29.5K, and the covalent mixing between the ruthenium and nearest-neighbor anions is described by A²_π = 8.2 ± 1% for Ba₂LaRuO₆ and 8.6 ± 1% for Ca₂LaRuO₆. The ionic radius of a Ru⁵⁺ ion is 0.56 Å. These data are consistently interpreted within the framework of a strongly correlated, half-filled π1 band. Extension of this interpretation to the magnetic data for the perovskites CaRuO₃ and SrRuO₃ leads to a fundamental theoretical prediction.