Spin-orbit induced mixed-spin ground state in $R$NiO${}_3$ perovskites probed by XAS: new insight into the metal to insulator transition

Abstract

We report on a Ni L${}_{2,3}$ edges x-ray absorption spectroscopy (XAS) study in $R$NiO${}_3$ perovskites. These compounds exhibit a metal to insulator ($MI$) transition as temperature decreases. The L${}_3$ edge presents a clear splitting in the insulating state, associated to a less hybridized ground state. Using charge transfer multiplet calculations, we establish the importance of the crystal field and 3d spin-orbit coupling to create a mixed-spin ground state. We explain the $MI$ transition in $R$NiO${}_3$ perovskites in terms of modifications in the Ni${}^{3+}$ crystal field splitting that induces a spin transition from an essentially low-spin (LS) to a mixed-spin state.

4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 2004