Magnetic transformations in the Sr0.78Y0.22Co1 − x Fe x O3 − γ system with a perovskite structure

Abstract

The Sr0.78Y0.22Co1 − xFexO3 − γ cobaltite system is studied by neutron and X-ray diffraction and by measuring the magnetization and elastic properties. The crystal structure of the composition with x = 0 is described in terms of the monoclinic space group A2/m with the unit cell 2 \( \sqrt 2 \)ap × 4ap × 2 \( \sqrt 2 \)ap, and the crystal structure of the composition with x = 0.12 is orthorhombic (space group Imma). The crystal structure of these compounds is characterized by alternating CoO6 and CoO4.5 layers. The magnetic structure is a G-type antiferromagnetic structure. The magnetic moments in the CoO6 layers are significantly higher than those in the CoO4.5 layers. In the compound with x = 0, magnetic measurements reveal a small ferromagnetic component (0.2 μB/Co) below TN ≈ 350 K. Near TN, a phase transformation occurs and lowers the crystallographic symmetry. Doping with iron ions suppresses the ferromagnetic component and sharply increases the average magnetic moments in both layers. The spontaneous magnetization is assumed to result from noncollinear magnetic moments, which can be caused by the competition of exchange interactions of different signs and magnetic anisotropy. The compounds with x = 0.5 and 1.0 are cubic (space group Pm3m) and are characterized by a G-type collinear antiferromagnetic structure.