Electronic correlations and long-range magnetic ordering in NiO tuned by pressure
G. M. Gaifutdinov, I. Leonov
Abstract
Using the density functional theory plus 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 (AFM) phase of NiO. We calculate the ordered magnetic moments and static magnetic 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 correlation effects to explain the insulating state of NiO. Upon compression, we observe a crossover from a charge transfer to the Mott-Hubbard insulating character of the insulating gap, with a predominant contribution from the majority Ni ${e}_{g}$ states near the Fermi level. The insulating state of AFM NiO is found to be stable up to a high compression $\ensuremath{\sim}0.4{V}_{0}$ (assuming the cubic $B1$ crystal structure of NiO). It is categorized as a correlation-assisted Slater-type insulator, implying the importance of long-range magnetic ordering. In fact, the paramagnetic phase of NiO at such high compression is found to be metallic, characterized by strong delocalization of the Ni $3d$ states. The calculated ${T}_{N}$ exhibits a nonmonotonic 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 nonlocal correlation effects to explain the magnetic properties of NiO.