Magnetic interactions and possible structural distortion in kagome FeGe from first-principles calculations and symmetry analysis

Abstract

Recently, charge density wave (CDW) order has been discovered in a magnetic kagome metal FeGe, providing a platform to explore the possible connection between magnetism and CDW in a kagome lattice. Based on density functional theory and symmetry analysis, we present a comprehensive investigation of electronic structure, magnetic properties, and possible structural distortion of FeGe. We estimate the magnetic parameters including Heisenberg and Dzyaloshinskii-Moriya (DM) interactions, and find that the ferromagnetic nearest-neighbor ${J}_{1}$ dominates over the others, while the magnetic interactions between nearest kagome layers favors antiferromagnetic. The N\'eel temperature ${T}_{N}$ and Curie-Weiss temperature ${\ensuremath{\theta}}_{\text{CW}}$ are successfully reproduced, and the calculated magnetic anisotropy energy is also consistent with the experimental results. However, these reasonable Heisenberg interactions and magnetic anisotropy cannot explain the double cone magnetic transition, and the DM interactions, which even exist in the centrosymmetric materials, can result in this small magnetic cone angle. Unfortunately, due to the crystal symmetry of the high-temperature structure, the net contribution of DM interactions to double cone magnetic structure is absent. Based on the experimental $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2$ supercell, we thus explore the subgroups of the parent phase. Group theoretical analysis reveals that there are 68 different distortions, and only four of them (space group $P622$ or $P{6}_{3}22$) without inversion and mirror symmetry thus can explain the low-temperature magnetic structure. Furthermore, we suggest that these four proposed CDW phases can be identified by using Raman spectroscopy. Since DM interactions are very sensitive to small atomic displacements and symmetry restrictions, we believe that symmetry analysis is a useful method to reveal the interplay of delicate structural distortions and complex magnetic configurations.