Cation order imaging and magnetic properties in the Ca2Fe2-xGaxO5 brownmillerite (0 ≤ x ≤ 1)

Polycrystalline Ca2Fe2-xGaxO5 brownmillerite samples of nominal x = 0.5, 0.7, 0.9 and 1 compositions have been synthesized by solid state reaction under normal pressure conditions. Whatever x is, room temperature structural analyses by Rietveld refinements and electron microscopy techniques highlight a centrosymmetric Pnma space group. Furthermore, STEM-HAADF observations point towards a preferential Ga occupation at the tetrahedral sites of the structure in agreement with the Rietveld analyses. The magnetic dilution by a diamagnetic cation is responsible for the TN decrease revealed by magnetization measurements and allows a spin flop transition to be observed.128