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)

摘要

By the first-principles electronic structure calculations, we find that theground state of the Fe-vacancies ordered TlFe$_{1.5}$Se$_2$ is aquasi-two-dimensional collinear antiferromagnetic semiconductor with an energygap of 94 meV, in agreement with experimental measurements. Thisantiferromagnetic order is driven by the Se-bridged antiferromagneticsuperexchange interactions between Fe moments. Similarly, we find that crystalsAFe$_{1.5}$Se$_2$ (A=K, Rb, or Cs) are also antiferromagnetic semiconductorsbut with a zero-gap semiconducting state or semimetallic state nearlydegenerated with the ground states. Thus rich physical properties and phasediagrams are expected.