Magnetic structures of Y2SrCu0.6Co1.4O6.5 and Y2SrCuFeO6.5

The nuclear and magnetic structures of two layered mixed copper transition- metal oxides Y2SrCU0.6Co1.4O6.5 and Y2SrCuFeO6.5 have been determined from time-of-flight neutron powder diffraction. Both compounds consist of apex-l inked pyramidal Cu/M-O-5 double layers,which alternate with oxygen defectiv e Y2O1.5 fluorite layers. The Go-containing compound has a simple magnetic structure with a Shubnikov group Ib'a'm. The magnetic moments (2.2 mu (B)) of this compound are aligned along the crystallographic b axis with antifer romagnetic order between neighboring Cu/Co ions. In contrast, the Fe-analog possesses a complicated noncolinear magnetic structure (Pc'c'n, with momen ts m perpendicular toc), which can also be considered as comprising two com ponents with I'bam' and Ib'a'm symmetry. The combination of the two compone nts results in an 82 degrees angle between the spins of Cu/Fe ions in neigh boring Cu/Fe-O-5 planes within a given double layer. The approximate 90 deg rees rotation of the moments results from a ferromagnetic interaction betwe en the neighboring Cu/Fe ions along the c axis through the apical oxygen at oms. The ferromagnetic component may originate from the Cu-z2(2)-O2p-Fed(z2 )(1) type exchange interaction. The implication of such an interaction to r elated layered cuprates is also discussed. By symmetry analysis, the magnet ic structure of the Co compound can be classified as a G(y)g type and the a ppearance of weak ferromagnetism can be attributed to the Dzyaloshinsky-Mor ia interaction which couples the G(y)g mode and F(z)f mode in the same repr esentation of the Ibam space group.