Spin-phonon scattering-induced low thermal conductivity in a van der Waals layered ferromagnet Cr${}_2$Si${}_2$Te${}_6$

Abstract

Layered van der Waals (vdW) magnets are prominent playgrounds for developing magnetoelectric, magneto-optic and spintronic devices. In spintronics, particularly in spincaloritronic applications, low thermal conductivity ($\hat{I}º$) is highly desired. Here, by combining thermal transport measurements with density functional theory calculations, we demonstrate low $\hat{I}º$ down to 1 W m${}^{-1}$ K${}^{-1}$ in a typical vdW ferromagnet Cr${}_2$Si${}_2$Te${}_6$. In the paramagnetic state, development of magnetic fluctuations way above $T_{\mathrm{c}}=$ 33 K strongly reduces $\hat{I}º$ via spin-phonon scattering, leading to low $\hat{I}º\sim$ 1 W m${}^{-1}$ K${}^{-1}$ over a wide temperature range, in comparable to that of amorphous silica. In the magnetically ordered state, emergence of resonant magnon-phonon scattering limits $\hat{I}º$ below $\sim$ 2 W m${}^{-1}$ K${}^{-1}$, which would be three times larger if magnetic scatterings were absent. Application of magnetic fields strongly suppresses the spin-phonon scattering, giving rise to large enhancements of $\hat{I}º$. Our calculations well capture these complex behaviours of $\hat{I}º$ by taking the temperature- and magnetic-field-dependent spin-phonon scattering into account. Realization of low $\hat{I}º$ which is easily tunable by magnetic fields in Cr${}_2$Si${}_2$Te${}_6$, may further promote spincaloritronic applications of vdW magnets. Our theoretical approach may also provide a generic understanding of spin-phonon scattering, which appears to play important roles in various systems.

14 pages, 6 figures, accepted for publication in Advanced Functional Materials