Electronic and magnetic structures of ternary iron selenides AFe$_2$Se$_2$ (A=K, Cs, or Tl)

TL;DR

This study uses first-principles calculations to reveal that ternary iron selenides AFe₂Se₂ (A=K, Cs, Tl) have a bi-collinear antiferromagnetic ground state driven by complex superexchange interactions.

Contribution

It is the first to identify the bi-collinear antiferromagnetic order as the ground state in these materials through electronic structure calculations.

Findings

Bi-collinear antiferromagnetic order found as ground state

Fe local moments approximately 2.8μ_B

Magnetic order driven by superexchange interactions

Abstract

By the first-principles electronic structure calculations, we find that the ground state of ternary iron selenides AFe$_2$Se$_2$ (A=K, Cs, or Tl) is in a bi-collinear antiferromagnetic order, in which the Fe local moments ($\sim2.8\mu_B$) align ferromagnetically along a diagonal direction and antiferromagnetically along the other diagonal direction on the Fe-Fe square lattice. This bi-collinear antiferromagnetic order results from the interplay among the nearest, the next nearest, and the next next nearest neighbor superexchange interactions, mediated by Se $4p$-orbitals.