Breakdown of the Hund's Rule in CuFeAs

TL;DR

This study uses density functional theory to reveal that CuFeAs's magnetic ground state violates Hund's rule due to Coulomb interactions and Cu vacancies, providing insights into its weak antiferromagnetism and reduced magnetism in iron pnictides.

Contribution

It demonstrates that Hund's rule breakdown in CuFeAs is driven by Coulomb interactions and vacancies, offering a new perspective on magnetism in iron-based materials.

Findings

Bicollinear antiferromagnetic state is favored by Coulomb interaction.

Hund's rule is violated in the ground state.

Weak antiferromagnetism explained by magnetic structure.

Abstract

The ground-state properties of CuFeAs were investigated by applying density functional theory calculations within generalized gradient approximation (GGA) and GGA+U. We find that the bicollinear antiferromagnetic state with antiparallel orbital magnetic moments on each iron which violates the Hund's rule is favored by the on-site Coulomb interaction, which is further stabilized by Cu vacancy. The magnetic ground state can be used to understand weak antiferromagnetism in CuFeAs observed experimentally. We argue that breakdown of the Hund's rule may be the possible origin for reduced magnetism in iron pnictides, rather than magnetic fluctuations induced by electronic correlations.