Effects of spin-phonon coupling on two-dimensional ferromagnetic semiconductors: a case study of iron and ruthenium trihalides

The contributions of spin-phonon coupling (SPC) to spin and thermal transport properties are important in emerging two-dimensional (2D) magnetic semiconductors and are relevant to the data security and working stability of spin-based devices. By evaluating the dynamical stability of both ferromagnetic (FM) and paramagnetic (PM) states at 0 K, six transition-metal trihalides, namely FeCl3, FeBr3, FeI3, RuCl3, RuBr3, and RuI3, are identified as ideal 2D magnetic semiconductors for investigating SPC. For these compounds, we perform first-principles calculations to evaluate the spin-relative lattice constants, bond angles, phonon dispersions, lattice thermal conductivity, as well as phonon-relative magnetic coupling parameters, magnetic moment, and Curie temperature. Our results suggest weaker SPC effects on Ru trihalides and stronger SPC effects on Fe trihalides. To explain these observations, we further analyze the SPC induced heat capacity, group velocity, scattering possibility, phonon anharmonicity, and phonon-magnon scattering. More importantly, we also provide a unified explanation for the SPC role in causing anomalous lattice thermal conductivity and stabilizing the ferromagnetic/antiferromagnetic ordering. The present study offers not only in-depth knowledge about the mechanisms of SPC regarding the spin and thermal transport behavior of 2D FM semiconductors, but also a better understanding of thermal management and control in magnetic quantum materials.