Spin dynamics in itinerant antiferromagnet SrCr${}_2$As${}_2$

Abstract

SrCr${}_2$As${}_2$ is an itinerant antiferromagnet in the same structural family as the SrFe${}_2$As${}_2$ high-temperature superconductors. We report our calculations of exchange-coupling parameters $J_{ij}$ for SrCr${}_2$As${}_2$ using a static linear-response method based on first-principles electronic-structure calculations. We find that the dominant nearest-neighbor exchange coupling $J_1>0$ is antiferromagnetic whereas the next-nearest-neighbor interaction $J_2<0$ is ferromagnetic with $J_2$/$J_1$~=~$-0.68$, 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 SrCr${}_2$As${}_2$, which aligns with experimental findings. Moreover, the orbital resolution of exchange interactions shows that $J_1$ and $J_2$ 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 $\hat{I}“$ 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.

9 pages, 9 figures