Decoupling of orbital and spin degrees of freedom in Li 1-xNaxNiO2

Abstract

In the Li1-xNaxNiO2 solid solutions, three different single-phase regions exist: for x≥0.9, for x≈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, particularly with respect to the low-temperature three-dimensional magnetic ordering. Therefore, the strong coupling between orbital and spin degrees of freedom, characteristic of other oxides like perovskites, and usually invoked to explain the absence of both long-range orbital and magnetic ordering in LiNiO2, does not take place in these layered compounds with ∼90° super-exchange bonds. We also discuss the relevance of the O crystal-field splitting induced by the trigonal distortion in generating antiferromagnetic in-plane Ni-Ni interactions.