Tunable spin transport and spin-dependent Seebeck effect in boron-based two-dimensional MBene transition metal compounds†

Abstract

Thermoelectric devices, which focus on the conversion of heat into electrical energy, are crucial for renewable energy applications. Spin caloritronics, a field that explores the interactions between heat, charge, and spin, has emerged as a promising area of research. By incorporating spin, new mechanisms and functionalities are introduced for more efficient thermal-to-electrical conversion. The spin Seebeck effect, which generates a voltage solely through a temperature gradient, represents a compelling branch of spin caloritronics, offering significant potential for advanced thermoelectric devices. In this study, we investigated three 2D transition metal borides, M₂B (M = Sc, Ti, and V), as candidates for spin and spin thermoelectric materials using first-principles calculations combined with density functional theory and nonequilibrium Green's function methods. Our calculations revealed that all three structures exhibited ferromagnetic states and metallic characteristics. Notably, the M₂B monolayers demonstrated exceptional electromagnetic properties, including high Curie temperatures and easy magnetization planes. Furthermore, these materials exhibited significant spin filtering effects (SFEs), negative differential resistance, and high magnetoresistance. We also found that spin-dependent currents were generated by applying a temperature gradient between the heat source and the cold source, suggesting the presence of thermally driven spin carrier transport. Additionally, thermal SFE and negative differential thermoelectric resistance were observed in M₂B (M = Sc, Ti, and V). The figure of merit of M₂B reached up to 3.0 at 300 K with a possibility of further enhancement by increasing the temperature T. Our results suggest the potential for boron-based 2D materials, specifically MBene, to serve as spin caloritronic materials, offering new design possibilities for low-power-consumption devices.