Effect of iron doping on magnetic properties of Sr0.78Y0.22CoO2.625+δ-layered perovskite

The Sr0.78Y0.22Co1-x Fe (x) O2.625+delta (x = 0 and 0.12) system has been studied using neutron diffraction technique, magnetization, and elastic properties measurements. Undoped sample exhibits superstructure with 2ae2a (p) * 2ae2a (p) * 4a (p) metrics and structural phase transition at T = 360 K. Magnetic ordering starts to develop below 360 K. Spontaneous magnetization shows anomalous behavior and reaches maximal value nearly room temperature. A magnetic structure of the both compounds has been described assuming G-type antiferromagnetic ordering. There are two different magnetic moment values for Co ions in CoO6 and CoO4.5 layers. Magnetic moments in CoO4.5 layers are larger than those for octahedrons. The refined values of magnetic moments indicate a mixed low-high spin state of Co3+ for the both layers. There is no evidence for any change of the magnetic structure type with temperature lowering despite the anomalous magnetization behavior. Iron doping (x = 0.12) leads to a suppression of the small ferromagnetic component, disappearance of the 2ae2a (p) * 2ae2a (p) * 4a (p) metrics, and strong increase of the average magnetic moment for Co-4.5 layer. It is suggested that the ferromagnetic component in the undoped samples is a result of non-collinearity of the magnetic moments within CoO4.5 layers.