First-Principles Study Of Magnon-Phonon Interactions In Gadolinium Iron Garnet

We obtained the spin-wave spectrum based on a first-principles method of exchange constants, calculated the phonon spectrum by the first-principles phonon calculation method, and extracted the broadening of the magnon spectrum Delta omega, induced by magnon-phonon interactions in gadolinium iron garnet (GdIG). Using the obtained exchange constants, we reproduce the experimental Curie temperature and the compensation temperature from spin models using METROPOLIS Monte Carlo (MC) simulations. In the lower-frequency regime, the fitted positions of the magnon-phonon dispersion crossing points are consistent with the inelastic neutron scattering experiment. We found that the Delta omega and magnon wave vector k have a similar relationship in YIG. The broadening of the acoustic spin-wave branch (alpha mode) is proportional to k(2), while that of the optical branch (beta and gamma modes) is a constant. At a specific k, the magnon-phonon thermalization times of tau(mp) are approximately 10(-9), 10(-13), and 10(-14) s for alpha, beta, and gamma modes, respectively. The results show the importance of the higher frequency modes at room temperature. This research provides specific and effective information for developing a clear understanding of the spin-wave mediated spin Seebeck effect and complements the lack of lattice dynamics calculations of GdIG.