Nonstoichiometric ${\mathrm{Sr}}_{1-y}{\mathrm{Mn}}_{1-z}{\mathrm{Sb}}_2(y,z<0.1)$ is known to exhibit a coexistence of magnetic order and the nontrivial semimetallic behavior. In this paper, we report the magnetism and its strong coupling to the semimetallic behavior, by a combined use of inelastic neutron scattering (INS) and density functional theory (DFT). A phase separation consisting of a majority antiferromagentic phase and a minority ferromagnetic phase is proposed. We found a relatively large spin excitation gap $\approx 8.5\mathrm{meV}$ at 5 K, and the interlayer magnetic exchange constant only 2.8% of the dominant intralayer magnetic interaction, evidencing a quasi-2D magnetism in ${\mathrm{Sr}}_{1-y}{\mathrm{Mn}}_{1-z}{\mathrm{Sb}}_2$. Using DFT, we find a strong influence of magnetic orders on the electronic band structure and the Dirac dispersions near the Fermi level along the Y-S direction in the presence of a ferromagnetic order. Furthermore, we demonstrate that the size of the ferromagnetic ordered moment is an effective strategy to tune Dirac/Weyl dispersions near the Fermi level. Our study unveils novel interplay between the magnetic order, ordered moment, and electronic band topology in ${\mathrm{Sr}}_{1-y}{\mathrm{Mn}}_{1-z}{\mathrm{Sb}}_2$ and opens pathways to control the relativistic band structure.

• Received 6 January 2019
• Revised 15 October 2019

DOI:https://doi.org/10.1103/PhysRevB.100.205105