Understanding Phonon Mediated Lattice Thermal Conductivity in Magnetic Trihalides

The investigation of phonon-mediated behaviours in transition metal trihalide systems is becoming an area of growing interest in fundamental research. The insulation of quantum magnet trihalides in both bulk and two-dimensional (2D) layers is a valuable avenue for investigating spin liquid phenomena, spintronics, magnetism in 2D and bulk systems, and thermal transport. The investigation of thermal transport mechanisms involving phonons in the presence of spins has received limited attention thus far. The present study has investigated the harmonic and anharmonic vibrational characteristics of magnetic bulk CrCl₃ and CrI₃ by the use of density functional theory (DFT) and subsequent experimental validation. Theoretical findings underscore the significance of van der Waals and magnetic interactions in ensuring the dynamical stability of these systems. The vibrational spectra of CrCl₃ and CrI₃ exhibit notable distinctions, mostly due to the presence of a phonon band gap in CrI₃. In particular, low-energy phonons in CrI₃ are predominantly influenced by iodine contributions. The phononic vibrational spectrum of CrCl₃ exhibits an intriguing anisotropic lattice thermal conductivity (κ_l), with higher κl values observed in the in-plane direction compared to CrI₃. Conversely, CrI₃ demonstrates larger κ_l values in the out-of-plane direction when compared to CrCl₃. It is demonstrated that despite the higher scattering strength of phonons in CrCl₃ due to its higher phonon group velocities, the heat transfer capacity of CrCl₃ surpasses that of CrI₃. Our study offers a fundamental comprehension and valuable insights into the phononic heat conduction in magnetic bulk transition metal trihalide materials.