Magnon-magnon interaction and magnon relaxation time in ferromagnetic Cr2Ge2Te6 monolayer

TL;DR

This paper introduces a first-principles method to analyze finite-temperature magnon-magnon interactions in 2D ferromagnetic materials, specifically applied to Cr2Ge2Te6 monolayer, revealing how magnon relaxation times vary with temperature, wavevector, and magnetic field.

Contribution

The paper develops a novel theoretical approach to incorporate finite-temperature magnon-magnon interactions into the Heisenberg Hamiltonian for 2D magnets.

Findings

Magnon relaxation time increases with temperature due to reduced magnon energy.

Magnon relaxation time decreases with wavevector and external magnetic field.

The method provides new insights into magnon damping in 2D ferromagnetic materials.

Abstract

Despite the intense amount of attention and huge potential of two-dimensional (2D) magnets for applications in novel magnetic, magneto-optical, magneto-thermal and magneto-electronic devices, there has yet to be a robust strategy developed to systematically understand magnon-magnon (MMI) interactions at finite temperature. In this paper, we present a first-principles theoretical method to introduce the finite temperature magnon-magnon interaction into Heisenberg Hamiltonian through a nonlinear correction energy. The Wick theorem is used to decouple the four-magnon operators to two-magnon order. We demonstrate the capabilities of this method by studying the strength of MMI in Cr2Ge2Te6 (CGT) monolayer. The spin wave spectrum at finite temperature and the time-dependent spin autocorrelation function are explored. It is found that the magnon relaxation time due to magnon-magnon scattering increases with temperature because of the reduction in magnon energy, while decreases with wavevector and external magnetic field. Our results provide a new insight to understand the magnon damping and energy dissipation in two-dimensional ferromagnetic materials.