Anomalous spin density distribution on oxygen and Ru in Ca$_{1.5}$Sr$_{0.5}$RuO$_4$: A polarised neutron diffraction study

TL;DR

This study uses polarized neutron diffraction to reveal an unexpected large magnetization density on oxygen in Ca$_{1.5}$Sr$_{0.5}$RuO$_4$, highlighting strong Ru-O hybridization and anisotropic orbital distribution.

Contribution

It provides the first direct measurement of anomalous oxygen magnetization and detailed orbital hybridization in Ca$_{1.5}$Sr$_{0.5}$RuO$_4$ using polarized neutron diffraction.

Findings

Large oxygen magnetization density observed

Quantified magnetic moments on Ru and O ions

Anisotropic magnetization density consistent with xy orbitals

Abstract

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 Ca$_{1.5}$Sr$_{0.5}$RuO$_4$. Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding $\mu$$_{Ru}$ = 0.346(11) $\mu$$_B$, $\mu_{O1}$ = 0.076(6) $\mu$$_B$ and $\mu_{O2}$ = 0.009(6) $\mu$$_B$. The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. %The maximum entropy method is used for the %reconstruction of the magnetization density and reveals a strongly anisotropic The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the {\it xy} ($t_{2g}$ band) {\it d}-orbitals.