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Nonstoichiometric Sr1-yMn1-zSb2(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 ≈8.5meV at 5 K, and the interlayer magnetic exchange constant only 2.8% of the dominant intralayer magnetic interaction, evidencing a quasi-2D magnetism in Sr1-yMn1-zSb2. 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 Sr1-yMn1-zSb2 and opens pathways to control the relativistic band structure.

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Physical Review B