Electronic structures and magnetic orders of Fe-vacancies ordered ternary iron selenides TlFe$_{1.5}$Se$_2$ and AFe$_{1.5}$Se$_2$ (A=K, Rb, or Cs)

TL;DR

This study uses first-principles calculations to reveal that Fe-vacancy ordered TlFe$_{1.5}$Se$_2$ and AFe$_{1.5}$Se$_2$ (A=K, Rb, Cs) are antiferromagnetic semiconductors with distinct electronic properties, highlighting complex phase behaviors.

Contribution

First-principles calculations identify the magnetic and electronic structures of Fe-vacancy ordered ternary iron selenides, revealing their antiferromagnetic semiconducting nature and near-degenerate states.

Findings

TlFe$_{1.5}$Se$_2$ is a collinear antiferromagnetic semiconductor with a 94 meV gap.

AFe$_{1.5}$Se$_2$ compounds are antiferromagnetic semiconductors with zero-gap or semimetallic states.

Rich phase diagrams are expected due to the near-degenerate electronic states.

Abstract

By the first-principles electronic structure calculations, we find that the ground state of the Fe-vacancies ordered TlFe$_{1.5}$Se$_2$ is a quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy gap of 94 meV, in agreement with experimental measurements. This antiferromagnetic order is driven by the Se-bridged antiferromagnetic superexchange interactions between Fe moments. Similarly, we find that crystals AFe$_{1.5}$Se$_2$ (A=K, Rb, or Cs) are also antiferromagnetic semiconductors but with a zero-gap semiconducting state or semimetallic state nearly degenerated with the ground states. Thus rich physical properties and phase diagrams are expected.