Spin reorientation driven by the interplay between spin-orbit coupling and Hund's rule coupling in iron pnictides

TL;DR

This paper investigates the origin of spin reorientation in iron pnictides, showing that the interplay between spin-orbit and Hund's rule couplings explains experimental observations without requiring orbital or nematic order.

Contribution

It introduces a microscopic model that accounts for spin anisotropy and reorientation in iron pnictides, highlighting the roles of spin-orbit and Hund's couplings.

Findings

Spin reorientation explained by spin-orbit and Hund's couplings.

Asymmetry between electron- and hole-doped magnetic states.

Reproduction of experimental magnetic ground states.

Abstract

In most magnetically-ordered iron pnictides, the magnetic moments lie in the FeAs planes, parallel to the modulation direction of the spin stripes. However, recent experiments in hole-doped iron pnictides have observed a reorientation of the magnetic moments from in-plane to out-of-plane. Interestingly, this reorientation is accompanied by a change in the magnetic ground state from a stripe antiferromagnet to a tetragonal non-uniform magnetic configuration. Motivated by these recent observations, here we investigate the origin of the spin anisotropy in iron pnictides using an itinerant microscopic electronic model that respects all the symmetry properties of a single FeAs plane. We find that the interplay between the spin-orbit coupling and the Hund's rule coupling can account for the observed spin anisotropies, including the spin reorientation in hole-doped pnictides, without the need to invoke orbital or nematic order. Our calculations also reveal an asymmetry between the magnetic ground states of electron- and hole-doped compounds, with only the latter displaying tetragonal magnetic states.