Structural and magnetic properties of Y_0.33Sr _0.67CoO_2.79

The perovskite-based oxide Y_0.33Sr_0.67CoO _2.79 has been magnetically and structurally characterized. The material shows a unit cell of 2 × 2 × 4 simple perovskite cubes with space group 14/mmm. This is a different structure to that observed in the much-studied (La,Sr)CoO₃ oxides. Oxygen stoichiometry is established through thermogravimetric analysis and correlated with ac and dc magnetic measurements and magnetic neutron diffraction. Hysteresis with field and temperature is observed in the dc magnetization measurements, yet the absence of an imaginary component in the ac susceptibility suggests a time-independent cause for these effects such as the presence of independently ordering ferromagnetic regions due to compositional inhomogeneities within the (single-phase) sample. Rietveld magnetic refinements suggest that the Co moments are arranged antiferromagnetically below 320 K, with the ferromagnetic regions existing within the long-range ordered antiferromagnetic matrix. The staggered moments are (anti)parallel with the c axis and of magnitude 2 μ_B, a moment most typical of intermediate spin Co³⁺. The material does not enter a spin glass or cluster glass phase, but appears to undergo a broad spin-state transition below 100 K.