Spin wave dispersion of 3d ferromagnets based on QSGW calculations

Abstract

We calculate transverse spin susceptibility in the linear response method based on the ground states determined in the quasi-particle self-consistent $GW$ (QSGW) method. Then we extract spin wave (SW) dispersions from the susceptibility. We treat bcc Fe, hcp Co, fcc Ni, and B2-type FeCo. Because of the better description of the independent-particle picture in QSGW, calculated spin stiffness constants for Fe, Co, and Ni give much better agreement with experiments in QSGW than that in the local density approximation (LDA), where the stiffness for Ni in LDA is two times bigger than the experiment. For Co, both acoustic and optical branches of SWs agree with the experiment. As for FeCo, we have some discrrepancy between the spin stiffness in QSGW and that in the experiment. We may need further theoretical and experimental investigations on the discrepancy.