Spin dynamics in itinerant antiferromagnet SrCr₂As₂

SrCr₂As₂ is an itinerant antiferromagnet in the same structural family as the SrFe2As2 high-temperature superconductors. We report our calculations of exchange coupling parameters Jᵢⱼ for SrCr₂As₂ using a static linear-response method based on first-principles electronic structure calculations. We find that the dominant nearest neighbor exchange coupling J₁ > 0 is antiferromagnetic whereas the next-nearest neighbor interaction J₂ < 0 is ferromagnetic with J₂/J₁~=~$-0.68$, reinforcing the checkerboard in-plane structure. Thus, unlike other transition-metal arsenides based on Mn, Fe, or Co, we find no competing magnetic interactions in SrCr₂As₂, which aligns with experimental findings. Moreover, the orbital resolution of exchange interactions shows that J₁ and J₂ are dominated by direct exchange mediated by the Cr d orbitals. To validate the calculations we conduct inelastic neutron-scattering measurements on powder samples that show steeply dispersive magnetic excitations arising from the magnetic Γ points and persisting up to energies of at least 175 meV. The spin-wave spectra are then modeled using the Heisenberg Hamiltonian with the theoretically calculated exchange couplings. The calculated neutron scattering spectra are in good agreement with the experimental data.