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−x Lax Co0.5Fe0.5O3−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 I 4/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 View the MathML sourcePm3¯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.