Quadrupole moments and their interactions in the triangular lattice antiferromagnet FeI$_2$

TL;DR

This paper investigates the role of quadrupole moments and their interactions in the triangular lattice antiferromagnet FeI$_2$, highlighting their implications for understanding the material's magnetic properties.

Contribution

It introduces the consideration of quadrupole interactions arising from orbital configurations, expanding the theoretical framework for FeI$_2$ and similar systems.

Findings

Quadrupole interactions are significant in FeI$_2$.

Orbital configurations influence quadrupole interactions.

Implications for magnetic behavior in triangular lattice antiferromagnets.

Abstract

Motivated by the recent experiments on the triangular lattice antiferromagnet FeI$_2$, we consider the presence of the quadrupole moments and their interactions between the spin-orbital-entangled local moments. In addition to the anisotropic pairwise interaction between the local moments, the interaction between the quadrupole moment arises from the interaction of the orbital occupation configurations. This is argued primarily from the time reversal symmetry and the different orbital configurations via their exchange paths. We discuss the implication of these interactions and expect this result to be complementary to the existing works in this system and other systems alike.