Crystal Structure and Ferromagnetic Component in Layered Perovskite Sr0.8Y0.2CoO2.65

Resumo

The crystal structure and magnetic state of Sr_0.8Y_0.2CoO_2.65 layered perovskite have been studied using neutron diffraction and synchrotron radiation diffraction and measuring the magnetization. It is shown that the crystal structure in the temperature range of 90–375 K can be described within the framework of the monoclinic sp. gr. A2/m with a cell 4√2a_p × 2√2a_p × 4a_p. The unit-cell parameter a is doubled (sp. gr. A2/m) below T_N ≈ 375 K. The basic magnetic structure can be described as G-type antiferromagnetic ordering with cobalt ion magnetic moments of 2.7 µ_B and 1.7 µ_B in the anion-deficient CoO_4+γ and stoichiometric CoO₆ layers, respectively. Based on the magnetization measurements, the ferromagnetic component of cobalt ion magnetic moment amounts to 0.27 µ_B at 8 K. In both layers, the Co³⁺ ions are predominantly in the mixed low/high-spin state. The ferromagnetic component is assumed to be due to the orbital ordering in the CoO₅ pyramids at T_N and the ferromagnetic exchange coupling between CoO₅ pyramids in anion-deficient layers.