Spin wave spectrum of 3d ferromagnet based on QSGW calculations

We have developed spin wave (SW) spectrum calculation code, combining quasi-particle self-consistent GW(QSGW) and maximum localized Wannier function (MLWF). With MLWF, we can overcome time-consuming calculations for large q-point SW spectrum. Since we adopt the linear response method for dynamical susceptibility^[1], our SW spectrum includes Stoner excitation, which causes the damping of spin SW. Stoner excitation is important in weak ferromagnet such as Fe, while not important in strong ferromagnet such as Ni. In the local density approximation (LDA), our SW energy in Fe is smaller than experimental result or other frozen SW calculation. In the QSGW calculations, due to the corrections of exchange splitting, the calculated SW stiffness constant of Ni (481 meV･Å in average) is in good agreement with inelastic neutron scattering experiment (483 meV･Å), while the LDA result (834 meV･Å) is almost twice as large as experimental one. In the fcc Co, our LDA result corresponds to frozen SW calculation because of weak Stoner excitation coupling in this strong ferromagnet. In the case of cubic FeCo in ordered state, we found acoustic and optical mode in the SW spectrum. [1] C. Friedrich, et al., First Principles Approaches to Spectroscopic Properties of Complex Materials pp 259-301 (2014).