Magnetic interactions and cluster formation: Boosting surface thermopower in topological insulators

This study presents a theoretical investigation of the thermoelectric properties of three-dimensional magnetic topological insulators (TIs), with a focus on the role of exchange interactions between magnetic dopants. The presence of these magnetic atoms on the TI surface modulates the local magnetic order, which in turn alters the electronic band structure and surface transport phenomena. Magnetic correlations, such as those arising from ferromagnetic or antiferromagnetic exchange, promote cluster formation, magnetic domain structures, and spin fluctuations, all of which critically influence thermoelectric responses. Using extensive Monte Carlo simulations based on Ising and Heisenberg models of these surface exchange interactions, we analyze how magnetic clustering, particularly near the surface critical temperature, affects relaxation dynamics, electrical and thermal resistivity, the Seebeck coefficient, and the thermoelectric figure of merit. Our results demonstrate that exchange-driven magnetic clustering enhances the scattering of Dirac surface states, thereby increasing the thermoelectric power factor. Specifically, optimized interlayer and intralayer exchange interactions can elevate the surface thermopower beyond levels observed in conventional spin-based thermoelectric materials. These findings highlight the significant potential of magnetic TIs for thermoelectric applications and provide a foundation for future experimental and theoretical studies of magnetic correlations in topologically nontrivial systems.