Annealing-tunable charge density wave in the kagome antiferromagnet FeGe

TL;DR

This study demonstrates that annealing treatments can tune the charge density wave and magnetic properties in FeGe, revealing an unconventional CDW mechanism linked to disorder on the Ge1 site in kagome antiferromagnets.

Contribution

It shows that annealing can induce a long-range CDW in FeGe and links this to disorder on the Ge1 site, offering new insights into CDW mechanisms in kagome materials.

Findings

Long-range CDW realized below 110 K after annealing at 320°C

CDW and AFM transition temperatures are inversely correlated

Disorder on Ge1 site modulates CDW and magnetic orders

Abstract

The unprecedented phenomenon that a charge density wave (CDW) emerges inside the antiferromagnetic (AFM) phase indicates an unusual CDW mechanism associated with magnetism in FeGe. Here, we demonstrate that both the CDW and magnetism of FeGe can be effectively tuned through post-growth annealing treatments. Instead of the short-range CDW reported earlier, a long-range CDW order is realized below 110 K in single crystals annealed at \SI{320}{\degreeCelsius} for over 48 h. The CDW and AFM transition temperatures appear to be inversely correlated with each other. The entrance of the CDW phase significantly reduces the critical field of the spin-flop transition, whereas the CDW transition remains stable against minor variations in magnetic orders such as annealing-induced magnetic clusters and spin-canting transitions. Single-crystal x-ray diffraction measurements reveal substantial disorder on the Ge1 site, which is characterized by displacement of the Ge1 atom from Fe$_3$Ge layer along the $c$ axis and can be reversibly modified by the annealing process. The observed annealing-tunable CDW and magnetic orders can be well understood in terms of disorder on the Ge1 site. Our study provides a vital starting point for the exploration of the unconventional CDW mechanism in FeGe and of kagome materials in general.