Spin dynamics in the itinerant antiferromagnet SrCr2As2

Abstract

SrCr2⁢As2 is an itinerant antiferromagnet in the same structural family as the SrFe2⁢As2 high-temperature superconductors. We report our calculations of exchange-coupling parameters 𝐽𝑖⁢𝑗 for SrCr2⁢As2 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 SrCr2⁢As2, 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.