ALaMnBO<SUB>6</SUB> (A=Ca, Sr, Ba; B=Fe, Ru) double perovskites

We report the synthesis and investigation of electrical and magnetic properties of double perovskites of the formula ALaMnBO6 for A = Ca, Sr, Ba and B = Fe, Ru. Powder X-ray diffraction (XRD) shows formation of cubic/pseudocubic perovskite structure for all the phases, with no obvious long-range ordering of B-site cations. Electron diffraction, however, reveals an ordering of Mn and Ru in ALaMnRuO6, showing a doubling of the primitive cubic perovskite cell. While the B = Fe phases are paramagnetic insulators, the B = Ru phases are ferrimagnetic semiconductors. It is likely that in the B = Ru phases, a valence equilibrium exists between MnIII/RuIV and MnII/RuV states that is biased toward the latter