A Dirac semimetal with magnetic atoms as constituents delivers an interesting platform to investigate the interplay of Fermi surface (FS) topology, electron correlation, and magnetism. One such family of semimetals is $\mathrm{YbMn}P{n}_2$ ($Pn=\text{Sb},\text{Bi}$), which is being actively studied due to the intertwined spin and charge degrees of freedom. Here, we investigate the relationship between the magnetic/crystal structures and FS topology of ${\mathrm{YbMnSb}}_2$ using single crystal x-ray diffraction, neutron scattering, magnetic susceptibility, magnetotransport measurements, and complimentary density functional theory (DFT) calculations. Contrary to previous reports, the x-ray and neutron diffraction reveal that ${\mathrm{YbMnSb}}_2$ crystallizes in an orthorhombic $Pnma$ structure with a notable antiphase displacement of the magnetic Mn ions that increases in magnitude upon cooling. As a result of this orthorhombicity, first-principles DFT calculation reveals a reduced Brillouin zone and more anisotropic FS of ${\mathrm{YbMnSb}}_2$ compared to ${\mathrm{YbMnBi}}_2$. Moreover, the hole-type carrier density drops by two orders of magnitude as ${\mathrm{YbMnSb}}_2$ orders antiferromagnetically, indicating band folding in a magnetic ordered state. In addition, the Landau level fan diagram yields a nontrivial nature of the Shubnikov–de Haas quantum oscillation frequency arising from the Dirac-like Fermi pocket. These results imply that ${\mathrm{YbMnSb}}_2$ is an ideal platform to explore the interplay of subtle lattice distortion, magnetic order, and topological transport arising from relativistic quasiparticles.

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• Antiferromagnetism
• Electronic structure
• Fermi surface
• Magnetism
• Magnetotransport
• Topological materials
• Crystal structures
• Magnetization measurements
• Neutron diffraction
• Resistivity measurements
• Shubnikov-de Haas effect
• X-ray diffraction