Abstract
Crystal and magnetic structures of complex manganese oxides and were studied by neutron powder diffraction (ND) and technique in the temperature range 2–300 K. The crystal structures contain single layers separated by three nonmagnetic cation-oxygen layers. The principal difference between the and compounds is the Mn valence: or and the structure of the buffer layer, which is formed by tetrahedra or partially filled octahedra, respectively. The magnetic moments of the manganese ions are coupled antiferromagnetically in the plane, but antiferromagnetically type) or ferromagnetically type) between the planes for the reduced and oxidized compositions, respectively. The transition from the G- to C-type magnetic structure by oxygen doping is explained by strong diagonal superexchange antiferromagnetic interaction between -ions in the adjacent layers through additional oxygen atoms in the GaO buffer layer. The magnetic moments in Sr-based samples are appreciably reduced in comparison with the spin-only values of the corresponding Mn ion. By using complementary information on local magnetic field distribution from we show that the reduced magnetic moments seen by ND are caused by the presence of locally flipped Mn spins and a short-ranged antiferromagnetic phase. The magnetic disorder can be caused by the disorder observed in the oxygen positions of the layer, because the coupling between the layers is mediated by the geometry of the superexchange path through these oxygen atoms.
- Received 17 June 2002
DOI:https://doi.org/10.1103/PhysRevB.66.184412
©2002 American Physical Society