Structural and Magnetic Characterisation of La1+xSr1–xCo0.5M0.5O4±δ (M = Cr, Mn)

The K 2 NiF 4 phases La 1+ x Sr 1– x Co 0.5 Cr 0.5 O 4± δ ( x = 0, 0.15) and La 1+ x Sr 1– x Co 0.5 Mn 0.5 O 4± δ ( x = 0, 0.2) have been synthesised and examined by X‐ray powder diffraction, thermal analysis, neutron powder diffraction and magnetic susceptibility measurements. Mn 3+ /Co 3+ and Cr 3+ /Co 3+ states predominate in the oxidised forms. Structural stability and crystal symmetry are retained under reducing conditions which cause reduction of Co 3+ into Co 2+ and the creation of oxide ion vacancies within the equatorial planes of the K 2 NiF 4 structure. Excess oxygen in La 1.2 Sr 0.8 Co 0.5 Mn 0.5 O 4.1 is accommodated in the ideal interstitial positions (0, 0.5, 0.25) of the tetragonal structure of these materials in an oxygen/air atmosphere. No long‐range magnetic order has been observed because of competing AFM and FM interactions in these B‐site disordered materials.