Exchange-mediated magnon-phonon scattering in monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">CrI</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>
Andi Cong, Jie Liu, Weishan Xue, Huicong Liu, Yi Liu, Ka Shen
Abstract
The interplay between magnons and phonons and its influences on magnon dissipation have attracted widespread attentions. Whereas the previous theoretical works were usually restricted to the interactions between low-frequency magnons and acoustic phonons in the long-wavelength region, in the present work we go beyond this limit and investigate the magnon relaxation in a two-dimensional ferromagnet, a monolayer ${\mathrm{CrI}}_{3}$, through magnon-phonon scattering channels mediated by the variation of the exchange strength resulting from all-wavelength acoustic phonons as well as the optical ones. With a precise description of the magnon and phonon Bloch states from first principles, we evaluate the magnon relaxation rate due to these exchange-mediated magnon-phonon scatterings and reveal rich features in its momentum dependence, which reflects nicely the role of the associated phonons with in-plane atomic vibrations. The magnon-number-conserving scattering is found to be orders of magnitude stronger than the magnon-number-nonconserving scattering due to the weak anisotropic exchange coupling or dipole-dipole interaction. Our first-principles-based approach provides a better solution for the quantitative evaluation of the magnon dissipation by phonons.