Electronic correlations and long-range magnetic ordering in NiO tuned by pressure

TL;DR

This study uses advanced computational methods to explore how pressure affects the electronic and magnetic properties of NiO, revealing a transition from insulating to metallic states and complex magnetic behavior.

Contribution

It provides a detailed pressure-temperature phase diagram of NiO using DFT+DMFT, highlighting the role of correlations and long-range magnetic order in its electronic structure.

Findings

NiO remains antiferromagnetic insulator up to high compression (~0.4 V0)

The Néel temperature shows non-monotonic behavior under pressure

High compression leads to a metallic paramagnetic phase

Abstract

Using the DFT+dynamical mean-field theory method we revisit the pressure-temperature phase diagram of the prototypical correlated insulator NiO. We study the pressure-induced evolution of the electronic structure, magnetic state, and exchange couplings of the antiferromagnetic phase of NiO. We calculate the ordered magnetic moments and uniform spin susceptibility of the Ni $3d$ states of NiO, which allow us to determine the pressure-dependence of the N\'eel temperature $T_N$. We note that the long-range magnetism has no significant effects on the valence band photoemission spectra of NiO under moderate compressions, implying the importance of correlations effects to explain the insulating state of NiO. The antiferromagnetic insulating state is found to be stable up to the high compression value $\sim$0.4 $V_0$ (assuming the cubic $B1$ crystal structure of NiO), and is associated with a (correlated-assisted) Slater insulating state driven by the long-range magnetic ordering. In fact, the paramagnetic phase of NiO at such high compression is found to be metallic, implying delocalization of the Ni $3d$ states. The calculated $T_N$ exhibits a non-monotonic behavior upon compression, with a maximum associated with the crossover from Mott localized (strong coupling) to itinerant moment regimes, in qualitative agreement with the phase diagram of the half-filled single-band Hubbard model. We point out the importance of the non-local correlation effects to explain the magnetic properties of NiO.