X-ray absorption study of the electronic structures of quasi-one-dimensional Co oxides Ca$_3$Co$Y$O$_6$ ($Y$ = Co, Rh, Ir, Mn)

Crystal structures of Sr$_{3}$NiIrO$_{6}$-type Ca$_{3}$Co$Y$O$_{6}$ ($Y$=Co, Rh, Ir, Mn) are characterized by the chains of alternating CoO$_{6}$ trigonal prisms and $Y$O$_{6}$ octahedra along $c$-axis. Since these chains form a triangular lattice in \textit{ab}-plane and interaction between chains is generally anti-ferromagnetic, magnetic frustration is expected to be observed in these compounds. Ca$_{3}$Co$_{2}$O$_{6}$ shows ferromagnetic-intrachain ordering and anti-ferromagnteic interchain coupling at 24 K and shows magnetic frustration between chains at 10-24 K. Ca$_{3}$CoRhO$_{6}$ also shows the same magnetic frustration at 30-90 K. But this magnetic frustration is not observed in Ca$_{3}$CoIrO$_{6}$ and Ca$_{3}$CoMnO$_{6}$. Direct information about their electronic structures is necessary to understand the mechanism of their interesting magnetic behavior. We have measured Co $2p$ and O $1s$ x-ray absorption spectra (XAS) of Ca$_{3}$Co$Y$O$_{6}$ ($Y$=Co, Rh, Ir, Mn) to study their electronic structures. In the O $1s $XAS spectra large spectral change has been observed in region of 526-528 eV. We will discuss the influence of the trigonal-prism-site Co $3d$ states on the magnetic interaction of Ca$_{3}$Co$Y$O$_{6}$.