Unveiling the Origin of the Basal-plane Antiferromagnetism in the Jeff=1/2 Mott Insulator Ba2IrO4: A Density Functional and Model Hamiltonian Study

TL;DR

This study combines density functional theory and a new model Hamiltonian to identify intralayer interactions as the cause of basal-plane antiferromagnetism in Ba2IrO4, highlighting the roles of single ion anisotropy and pseudo-quadrupole interactions.

Contribution

It introduces a novel model Hamiltonian including single ion anisotropy and pseudo-quadrupole interactions to explain antiferromagnetism in Ba2IrO4.

Findings

Intralayer magnetic interactions cause basal-plane antiferromagnetism.

Single ion anisotropy and pseudo-quadrupole interactions are unexpectedly strong.

Magnetism is driven by isotropic Heisenberg, Kitaev, and pseudo-quadrupole interactions.

Abstract

Based on the density functional theory and our new model Hamiltonian, we have studied the basal-plane antiferromagnetism in the novel Jeff=1/2 Mott insulator Ba2IrO4. By comparing the magnetic properties of the bulk Ba2IrO4 with those of the single-layer Ba2IrO4, we demonstrate unambiguously that the basal-plane antiferromagnetism is caused by the intralyer magnetic interactions rather than by the previously proposed interlayer ones. In order to reveal the origin of the basal-plane antiferromagnetism, we propose a new model Hamiltonian by adding the single ion anisotropy and pseudo-quadrupole interactions into the general bilinear pseudo-spin Hamiltonian. The obtained magnetic interaction parameters indicate that the single ion anisotropy and pseudo-quadrupole interactions are unexpectedly strong. Systematical Monte Carlo simulations demonstrate that the basal-plane antiferromagnetism is caused by the isotropic Heisenberg, bond-dependent Kitaev and pseudo-quadrupole interactions. Our results show for the first time that the single ion anisotropy and pseudo-quadrupole interaction can play significant roles in establishing the exotic magnetism in the Jeff=1/2 Mott insulator.