Simultaneous development of antiferromagnetism and local symmetry breaking in a kagome magnet (Co$_{0.45}$Fe$_{0.55}$)Sn

TL;DR

This study reveals that Fe-doping in a kagome magnet induces simultaneous antiferromagnetic order and local symmetry breaking, linked to lattice distortions and magnetic interactions, providing new insights into their coupled physical properties.

Contribution

It demonstrates the co-emergence of antiferromagnetism and local symmetry breaking in (Co0.45Fe0.55)Sn, highlighting the interplay between magnetic order and local structural distortions.

Findings

Antiferromagnetic order with moments perpendicular to kagome layers.

Local orthorhombic distortion involving Sn displacements.

Lattice instability below the Néel temperature due to magnetic ordering.

Abstract

CoSn and FeSn, two kagome-lattice metals, have recently attracted significant attention as hosts of electronic flat bands and emergent physical properties. However, current understandings of their physical properties are limited to the knowledge of the average crystal structure. Here, we report the Fe-doping induced co-emergence of the antiferromagentic (AFM) order and local symmetry breaking in (Co0.45Fe0.55)Sn. Rietveld analysis on the neutron and synchrotron x-ray diffraction data indicates A-type antiferromagnetic order with the moment pointing perpendicular to the kagome layers, associated with the anomaly in the MSn(1)2Sn(2)4 (M = Co/Fe) octahedral distortion and the lattice constant c. Reverse Monte Carlo (RMC) modeling of the synchrotron x-ray total scattering results captured the subtle local orthorhombic distortion involving off-axis displacements of Sn2. Our results indicate that the stable hexagonal lattice above TN becomes unstable once the A-type AFM order is formed below TN. We argue that the local symmetry breaking has a magnetic origin and is driven by the out-of-plane magnetic exchange coupling. Our study provides comprehensive information on the crystal structure in both long-range scale and local scale, unveiling unique coupling between AFM order, octahedral distortion, and hidden local symmetry breaking.