Orbital Properties of Sr3Ru2O7 and Related Ruthenates Probed by 17O-NMR

TL;DR

This study uses 17O-NMR to analyze the orbital and spin properties of Sr3Ru2O7 and related ruthenates, revealing large covalent character and the importance of oxygen site densities in their magnetic behavior.

Contribution

It provides detailed site-specific orbital and spin information in layered ruthenates, highlighting the role of oxygen in their complex magnetism, which was not previously well understood.

Findings

Large hole occupancies at oxygen sites due to covalent Ru-O bonding

Spin densities at oxygen sites are significant and vary with dimensionality

Oxygen density-of-states is crucial for understanding ruthenate magnetism

Abstract

We report a site-separated $^{17}$O-NMR study of the layered perovskite ruthenate Sr$_3$Ru$_2$O$_7$, which exhibits nearly two-dimensional transport properties and itinerant metamagnetism at low temperatures. The local hole occupancies and the spin densities in the oxygen $2p$ orbitals are obtained by means of tight-binding analyses of electric field gradients and anisotropic Knight shifts. These quantities are compared with two other layered perovskite ruthenates: the two-dimensional paramagnet Sr$_2$RuO$_4$ and the three-dimensional ferromagnet SrRuO$_3$. The hole occupancies at the oxygen sites are very large, about one hole per ruthenium atom. This is due to the strong covalent character of the Ru-O bonding in this compound. The magnitude of the hole occupancy might be related to the rotation or tilt of the RuO$_6$ octahedra. The spin densities at the oxygen sites are also large, 20-40% of the bulk susceptibilities, but in contrast to the hole occupancies, the spin densities strongly depend on the dimensionality. This result suggests that the density-of-states at the oxygen sites plays an essential role for the understanding of the complex magnetism found in the layered perovskite ruthenates.