First Observation of MCD at O and Ru sites in Sr$_{4}$Ru$_{3}$O$_{10}$

Perovskite strontium ruthenates of the Ruddlesden-Popper (RP) series Sr $_{n+1}$Ru$_{n }$O$_{3n+1 }$show a variety of complex behavior including superconductivity and metamagnetism. Sr$_{4}$Ru$_{3}$O$_{10}$ is a trilayer member of the RP series with n=3 that is metamagnetic and shows an electronic phase separation$^{1}$. We wanted to test if this material showed magnetic behavior at low fields and performed magnetic circular dichroism measurements (MCD) at the O K and Ru L edges. The measurements were carried out at the Sector 4 polarization beam line of the Advanced Photon Source at grazing (10\r{ }) and normal incidence angles at the characteristic temperature 50K ~below which ~metamagnetic behavior occurs$^{2}$ and above the ordering temperature (150K). We observed dichroic behavior at both temperatures although the dichroism was reduced by a factor of 10 at 150K relative to the measurements at 50K. It is significant to note that only the lowest unoccupied orbital (LUMO) associated with the planar O site showed dichroic behavior. This research was supported in part by DOE grant No. DE-FG02-05ER-46183, and the Advanced Photon Source is supported by DOE grant W-31-109-ENG-38. \begin{enumerate} \item Z.Q. Mao et al, submitted to Physical Review Letter. \item G. Cao et al, Phys. Rev. B \textbf{68}, 174409 (2003) \end{enumerate}