Orbital Angular Momentum of Magnons in Collinear Magnets

TL;DR

This paper investigates how the orbital angular momentum of magnons in collinear ferromagnetic and antiferromagnetic systems is influenced by lattice structure and exchange interactions, revealing new mechanisms beyond spin-orbit coupling.

Contribution

It demonstrates that the lattice arrangement of exchange interactions can induce nonzero magnon orbital angular momentum in collinear magnets, independent of spin-orbit effects.

Findings

Orbital angular momentum of magnons is nonzero in certain lattice geometries.

Maximum orbital angular momentum occurs at band extremum or avoided crossings.

Lattice structure influences magnon orbital angular momentum more than spin-orbit coupling.

Abstract

We study the orbital angular momentum of magnons for collinear ferromagnet (FM) and antiferromagnetic (AF) systems with nontrivial networks of exchange interactions. The orbital angular momentum of magnons for AF and FM zig-zag and honeycomb lattices becomes nonzero when the lattice contains two inequivalent sites and is largest at the avoided-crossing points or extremum of the frequency bands. Hence, the arrangement of exchange interactions may play a more important role at producing the orbital angular momentum of magnons than the spin-orbit coupling energy and the resulting non-collinear arrangement of spins.