FeGe1−xSbx : A series of kagome metals with noncollinear antiferromagnetism

Kagome metals are important for exploring emergent phenomena due to the interplay between band topology and electron correlation. Motivated by the recent discovery of charge density waves in the kagome lattice antiferromagnet FeGe, we investigate the impact of Sb doping on the structural, charge, and magnetic order of FeGe. The superlattice distortion induced by charge order disappears with only slight Sb doping ($\ensuremath{\sim}1.5$%) down to 80 K. The antiferromagnetic ordering temperature gradually shifts to 280 K for ${\mathrm{FeGe}}_0.7{\mathrm{Sb}}_0.3$. For ${\mathrm{FeGe}}_{1\ensuremath{-}x}{\mathrm{Sb}}_x$ with $x\ensuremath{\geqslant}0.1$, crystal structures with a slightly distorted Fe kagome lattice are formed. A significant change in magnetic anisotropy from easy axis to easy plane with increasing $x$ is identified from magnetization measurements. Interestingly, neutron diffraction reveals noncollinear antiferromagnetic structures widely exist below ${T}_N$ for all samples with $x\ensuremath{\geqslant}0.1$. These noncollinear magnetic orders could possibly be unconventional and result from on-site repulsion and filling conditions of the kagome flat band, as predicted by a recent theoretical work.