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

The Sr 0.78 Y 0.22 Co 1− x Fe x O 2.625+δ ( x = 0 and 0.12) system has been studied using neutron diffraction technique, magnetization, and elastic properties measurements. Undoped sample exhibits superstructure with 2√2a p * 2√2a 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 CoO 6 and CoO 4.5 layers. Magnetic moments in CoO 4.5 layers are larger than those for octahedrons. The refined values of magnetic moments indicate a mixed low–high spin state of Co 3+ 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 2√2a p * 2√2a 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 CoO 4.5 layers.