Vortex Crystals with Chiral Stripes in Itinerant Magnets

TL;DR

This paper investigates noncoplanar magnetic orderings in frustrated itinerant magnets, revealing that vortex crystal states are energetically favored due to Fermi surface instabilities, especially under specific lattice symmetries and electron fillings.

Contribution

It demonstrates that vortex crystal magnetic states are energetically favored over helical orders in certain Kondo lattice models due to Fermi surface instabilities, expanding understanding of magnetic orderings.

Findings

Vortex crystal states have lower energy than helical orders under specific conditions.

Noncoplanar states arise from Fermi surface instabilities.

The phenomenon is generic across various electron fillings and lattice symmetries.

Abstract

We study noncoplanar magnetic ordering in frustrated itinerant magnets. For a family of Kondo square lattice models with classical local moments, we find that a double-$Q$ noncoplanar vortex crystal has lower energy than the single-$Q$ helical order expected from the Ruderman-Kittel-Kasuya-Yosida interaction whenever the lattice symmetry dictates four global maxima in the bare magnetic susceptibility. By expanding in the small Kondo exchange and the degree of noncoplanarity, we demonstrate that this noncoplanar state arises from a Fermi surface instability, and it is generic for a wide range of electron filling fractions whenever the two ordering wave vectors connect independent sections of the Fermi surface.