Pressure-driven magnetic moment collapse in the ground state of MnO

TL;DR

This study uses correlated band theory to investigate pressure-induced magnetic moment collapse in MnO, revealing an unexpected spin-flip transition that impacts its electronic and magnetic properties.

Contribution

It uncovers a novel insulator-insulator transition involving a Hund's rule violating spin-flip in MnO under pressure, expanding understanding of Mott transitions.

Findings

Identification of a pressure-induced insulator-insulator transition

Discovery of a Hund's rule violating spin-flip moment collapse

Robustness of the spin-flip state across interaction strengths and structures

Abstract

The zero temperature Mott transition region in antiferromagnetic, spin S=5/2 MnO is probed using the correlated band theory LSDA+U method. The first transition encountered is an insulator-insulator volume collapse within the rocksalt structure that is characterized by an unexpected Hund's rule violating `spin-flip' moment collapse. This spin-flip to S=1/2 takes fullest advantage of the anisotropy of the Coulomb repulsion, allowing gain in the kinetic energy (which increases with decreasing volume) while retaining a sizable amount of the magnetic exchange energy. While transition pressures vary with the interaction strength, the spin-flip state is robust over a range of interaction strengths and for both B1 and B8 structures.