Magnetic interactions and excitations in SrMnSb2

The magnetic interactions in the antiferromagnetic (AFM) Dirac semimetal candidate SrMnSb2 are investigated using ab initio linear response theory and inelastic neutron scattering (INS). Our calculations reveal that the first two nearest in-plane couplings (J1 and J2) are both AFM in nature, indicating a significant degree of spin frustration, which aligns with experimental observations. The orbital resolution of exchange interactions shows that J1 and J2 are dominated by direct and superexchange, respectively. In a broader context, a rigid-band model suggests that electron doping fills the minority spin channel and results in a decrease in the AFM coupling strength for both J1 and J2. To better compare with INS measurements, we calculate the spin-wave spectra within a linear spin-wave theory, utilizing the computed exchange parameters. Although the calculated spin-wave spectra somewhat overestimate the magnon bandwidth, they exhibit overall good agreement with measurements from INS experiments.