A study of the new K2NiF4-type solid solutions Sr2FexRu1−xO4 by Mőssbauer spectroscopy and other techniques

The magnetic and structural properties of the solid solutions Sr₂Fe_xRu_1?xO₄ (O ? x ? 0.5) have been studied using ⁵⁷Fe and ⁹⁹Ru Mőssbauer spectroscopy and other techniques. These phases, which are reported for the first time, have the K₂NiF₄-type structure with iron and ruthenium distributed at random on the B-site. As the ruthenium is replaced by iron the weakly-metallic conductivity and Pauli paramagnetism of Sr₂RuO₄ give way to localized-electron behaviour and long-range antiferromagnetic order despite the layer-type structure which is unfavourable for 180° Ru-O-M (M = Fe or Ru) magnetic exchange interactions in three dimensions. For x = 0.1-0.4 the iron is present almost entirely in the +3 oxidation state, but for x = 0.5 appreciable amounts of Fe^IV are also present, in conjunction with Fe^III, Ru^IV, and Ru^V.