Decoupling of orbital and spin degrees of freedom in Li1-xNaxNiO2

TL;DR

This study investigates the decoupling of orbital and spin degrees of freedom in Li1-xNaxNiO2, revealing that strong coupling seen in other oxides does not occur in these layered compounds, despite similar magnetic properties.

Contribution

It demonstrates the decoupling of orbital and spin degrees of freedom in Li1-xNaxNiO2, challenging the assumption of strong coupling in layered oxides with 90-degree bonds.

Findings

Intermediate compositions lack cooperative Jahn-Teller transition

Magnetic ordering persists despite absence of orbital order

Trigonal distortion influences in-plane AFM interactions

Abstract

In the Li1-xNaxNiO2 solid solutions three different single phase regions exist: for x > 0.9, forx = 0.7 and for x < 0.3. Although the intermediate compound does not show the cooperative Jahn-Teller transition of NaNiO2, its magnetic properties remain very similar with, in particular, the low temperature 3D magnetic ordering. Therefore, the strong coupling between orbital and spindegrees of freedom, characteristic of other oxides like perovskites, and usually invoked to explainthe absence of both long-range orbital and magnetic ordering in LiNiO2, seems not to take placein these layered compounds with 90-degree bonds. We also discuss the relevance of the O crystal fieldsplitting induced by the trigonal distortion, in generating AFM Ni-Ni in-plane interactions.