Ferro-Orbital Order and Strong Magnetic Anisotropy in the Parent Compounds of Iron-Pnictide Superconductors

TL;DR

This study reveals ferro-orbital ordering as the key driver of magnetic anisotropy and phase transitions in iron pnictides, highlighting the importance of orbital physics in their electronic structure and spin dynamics.

Contribution

It uncovers ferro-orbital order as the origin of magnetic anisotropy and phase transitions in iron pnictides, challenging previous frustration-based explanations.

Findings

Ferro-orbital ordering causes magnetic anisotropy.

Orbital physics is essential for understanding phase transitions.

Strong magnon coupling suggests active orbital roles in spin dynamics.

Abstract

The puzzling nature of magnetic and lattice phase transitions of iron pnictides is investigated via a first-principles Wannier function analysis of representative parent compound LaOFeAs. A rare ferro-orbital ordering is found to give rise to the recently observed highly anisotropic magnetic coupling, and drive the phase transitions--without resorting to widely employed frustration or nesting picture. The revealed necessity of the additional orbital physics leads to a correlated electronic structure fundamentally distinct from that of the cuprates. In particular, the strong coupling to the magnons advocates active roles of light orbitons in spin dynamics and electron pairing in iron pnictides.