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

TL;DR

This study uses X-ray absorption spectroscopy to reveal how spin-orbit coupling and crystal field effects induce a mixed-spin ground state in $R$NiO$_3$ perovskites, shedding light on their metal-insulator transition mechanism.

Contribution

It demonstrates the role of spin-orbit coupling and crystal field modifications in driving the spin transition associated with the metal-insulator transition in $R$NiO$_3$.

Findings

Splitting at Ni L3 edge correlates with insulating state.

Mixed-spin ground state is induced by spin-orbit coupling.

Metal-insulator transition linked to spin state change.

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.