Spin dynamics in the 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 exchange coupling J2<0 is ferromagnetic with J2/J1 = -0.68, reinforcing the checkerboard in-plane magnetic 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.