Theory of the magnetic and metal-insulator transitions in RNiO3 bulk and layered structures

TL;DR

This paper develops a theoretical framework using slave rotor-Hartree Fock formalism to study magnetic and metal-insulator transitions in RNiO3 compounds, capturing phase diagram features and effects of thin-film morphology and strain.

Contribution

It introduces a unified numerical formalism for the p-d model that accurately describes phase transitions and magnetic order in rare earth nickelates, including thin-film effects.

Findings

Reproduces the paramagnetic metal state of LaNiO3.

Correctly predicts magnetic order of insulating nickelates.

Shows epitaxial strain and charge transfer significantly affect phase diagrams.

Abstract

A slave rotor-Hartree Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within an unified formulation, the significant aspects of the rare earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and un-strained thin-film form. For ultrathin films, epitaxial strain and charge-transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram.