Nano-scale collinear multi-Q states driven by higher-order interactions

TL;DR

This paper demonstrates that higher-order interactions can stabilize collinear multi-Q magnetic states at the nano-scale in two-dimensional itinerant magnets, expanding understanding of complex magnetic orders beyond Dzyaloshinskii-Moriya interactions.

Contribution

It introduces a new mechanism for stabilizing collinear nano-scale multi-Q states via higher-order interactions in 2D itinerant magnets, supported by experimental and theoretical analysis.

Findings

Observation of zero-field nano-scale magnetic states via STM

Identification of higher-order interactions as key stabilizers

Discovery of collinear multi-Q states driven by these interactions

Abstract

Complex magnetic order arises due to the competition of different interactions between the magnetic moments. Recently, there has been an increased interest in such states not only to unravel the fundamental physics involved, but also with regards to applications exploiting their unique interplay with moving electrons. Whereas it is the Dzyaloshinskii-Moriya interaction (DMI) that has attracted much attention because of its nature to induce non-collinear magnetic order including magnetic-field stabilized skyrmions, it is the frustration of exchange interactions that can drive magnetic order down to the nano-scale. On top of that, interactions between multiple spins can stabilize two-dimensional magnetic textures as zero-field ground states, known as multi-Q states. Here, we introduce a two-dimensional itinerant magnet with various competing atomic-scale magnetic phases. Using spin-polarized scanning tunneling microscopy we observe several zero-field uniaxial or hexagonal nano-scale magnetic states. First-principles calculations together with an atomistic spin model reveal that these states are stabilized by the interplay of frustrated exchange and higher-order interactions while the DMI is weak. Unexpectedly, it is found that not only non-collinear magnetic states arise, but that higher-order interactions can also lead to collinear nano-scale multi-Q states.