Anomalous Spin-Density Distribution on Oxygen and Ru inCa1.5Sr0.5RuO4: Polarized Neutron Diffraction Study

By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in ${\mathrm{C}\mathrm{a}}_{1.5}{\mathrm{S}\mathrm{r}}_{0.5}{\mathrm{R}\mathrm{u}\mathrm{O}}_4$. Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding ${\mu }_{\mathrm{R}\mathrm{u}}=0.346(11){\mu }_B$, ${\mu }_{\mathrm{O}1}=0.076(6){\mu }_B$, and ${\mu }_{\mathrm{O}2}=0.009(6){\mu }_B$. The moment on the oxygen arises from the strong hybridization between the $\mathrm{R}\mathrm{u}-4d$ and $\mathrm{O}-2p$ orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the $xy$ ($t_{2g}$ band) $d$ orbitals.