The Sr 1-x Y x CoO 2.65 (x=0.2) with layered perovskite structure was studied by neutron diffraction, synchrotron X-ray and magnetometry methods. It is shown that in the 90-375 K temperature range the crystal structure can be described by the monoclinic space group A2/m with the superstructure 4√2a p × 2√2a p × 4a p (a p is a primitive cell) however basic diffraction peaks well indexed in I4/mmm (2a p × 2a p × 4a p) space group. Around theNeel point T N = 375 K there is a doubling of the unit cell parameter along a axis in the framework of the space group A2/m. A basic magnetic structure is G type antiferromagnetic with average magnetic moments of 2.7μ B /Co and 1.7μ B /Co in anion-deficient CoO 4 + γ and stoichiometric CoO 6 layers, respectively. The ferromagnetic component determined from the magnetization measurements is about 0.27μ B /Co at 8 K. Sr 0.8 Y 0.2 CoO 2.65 shows almost standard magnetization vs. temperature dependence whereas Sr 0.75 Y 0.25 CoO 2.65 exhibitsantiferromagnet-ferromagnet transition accompanied by structural transformation. There is practically no spontaneous magnetization in x=0.3.The basic magnetic structure and high T N suggest that Co 3 + ions in both structural layers are predominantly in the low-spin /high-spin states mixture. It is assumed that the ferromagnetic component is due to the orbital ordering occurring at T N in the CoO 5 pyramids and concomitantappearance of ferromagnetic exchange coupling between the Co 3+ (HS)ions located in CoO 5 pyramids in anion-deficientCoO 4 + γ layer.

The properties of Sr1−xYxCoO3−δ layered cobaltites are determined by synchrotron X‐ray and neutron powder diffraction studies, by measurements of magnetic and magnetotransport properties. It is shown that the crystal structure changes from tetragonal P4/mmm (ap × ap × 2ap) to monoclinic A2/m (4√2ap × 2√2ap×4ap up to the magnetic ordering temperature and 2√2ap ×2√2ap × 4ap above) through the intermediate tetragonal I4/mmm (2ap × 2ap × 4ap) with alternating layers of CoO6 and CoO4+δ. The basic magnetic structure is G‐type antiferromagnetic with Co3+ ions in a high spin/low spin (HS/LS) state mixture in both structural layers. The Co3+ magnetic moments in the CoO6 and CoO4+δ layers are 1.5 μB/Co and 2 μB/Co for x = 0.1 and 1.8 μB/Co and 2.7 μB/Co for x = 0.2, respectively. The antiferromagnetic–“ferromagnetic” transition in compounds with x > 0.2 is associated with the structural and orbital disorder. Magnetic transitions are accompanied by structural phase transitions. The presence of the ferromagnetic component is associated with the monoclinic distortions and canting of magnetic moments in anion‐deficient layers due to orbital ordering. A sharp drop of the magnetization for x > 0.2 is caused by the LS Co3+ stabilization and orbital disordering. No spontaneous magnetization is found for compounds with x > 27%.

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