Crystal structure and magnetic properties of high-oxygen pressure annealed Sr1−xLaxCo0.5Fe0.5O3−δ (0⩽x⩽0.5)

Structural and magnetic studies are presented for the perovskite type Sr1−xLaxCo0.5Fe0.5O3−δ (0⩽x⩽0.5) materials annealed under moderately high-oxygen pressures of ∼200 atm. A detailed analysis of the room temperature neutron time-of-flight diffraction data reveals that the crystal structure of the sample SrCo0.5Fe0.5O2.89(1), previously described as vacancy-disordered cubic, is similar to the formerly reported, oxygen-vacancy ordered Sr8Fe8O23 compound, i.e. Sr8Co4Fe4O23 is tetragonal with the I4/mmm   symmetry. With an increase of the La content the studied materials become nearly oxygen stoichiometric and a lowering of the crystal symmetry is observed from cubic Pm3¯m (x=0.1 and 0.2) to tetragonal I4/mcm (x=0.3 and 0.4), and finally to monoclinic I12/c1 (x=0.5). Low-temperature structural and magnetic measurements show a ferromagnetic ordering with the maximum Curie temperature near 290 K at x=0.2.

Graphical AbstractRoom temperature Rietveld refinement profile using I4/mmm space group for the oxygen vacancy ordered SrCo0.5Fe0.5O2.89 (Sr8Co4Fe4O23). Top tick-marks denote allowed reflections in I4/mmm  , bottom one emphasize the possibility of inexact indexing using Pm3¯m symmetry. Previous reports indicate that similar ordering is common for SrCo1−xFexO3−δ compounds possibly hindering their applications.Figure optionsDownload as PowerPoint slide