Enhanced spin thermoelectric effects in BN-embedded zigzag graphene nanoribbons

Thermal transport and spin-dependent Seebeck effect in parallel step-like zigzag graphene nanoribbon junctions

By using nonequilibrium molecular dynamics, thermal transport through a series of parallel step-like graphene nanoribbon (GNR) junctions is investigated. The theoretical results show that the thermal current flows preferentially from wide GNRs to narrow ones, displaying a pronounced thermal rectification effect. Moreover, several step-like GNR-based devices are designed, and the thermally driven spin-dependent currents are calculated by using density functional theory combined with the nonequilibrium Green's function approach. We find that thermal spin-dependent currents with opposite flow directions are generated when a temperature gradient is applied along the GNRs, indicating the occurrence of a spin-dependent Seebeck effect (SDSE). More interestingly, a negative differential SDSE occurs in the thermal spin currents, and the odd and even law appears in the spin-dependent currents, thermopowers and thermoelectric conversion efficiencies. Our theoretical results indicate that the parallel step-like GNRs are potential candidates to design spin caloritronics devices hosting thermal rectification and multiple thermal-spin transport functionalities.

Metal-free magnetism, spin-dependent Seebeck effect, and spin-Seebeck diode effect in armchair graphene nanoribbons

Metal-free magnetism and spin caloritronics are at the forefront of condensed-matter physics. Here, the electronic structures and thermal spin-dependent transport properties of armchair graphene nanoribbons (N-AGNRs), where N is the ribbon width (N = 5-23), are systematically studied. The results show that the indirect band gaps exhibit not only oscillatory behavior but also periodic characteristics with E _3p  > E_3p+1 > E_3p+2 (E _3p , E_3p+1 and E_3p+2 are the band gaps energy) for a certain integer p, with increasing AGNR width. The magnetic ground states are ferromagnetic (FM) with a Curie temperatures (T _C ) above room temperature. Furthermore, the spin-up and spin-down currents with opposite directions, generated by a temperature gradient, are almost symmetrical, indicating the appearance of the perfect spin-dependent Seebeck effect (SDSE). Moreover, thermally driven spin currents through the nanodevices induced the spin-Seebeck diode (SSD) effect. Our calculation results indicated that AGNRs can be applied in thermal spin nanodevices.

Giant spin thermoelectric effects in all-carbon nanojunctions

We investigate the thermospin properties of an all-carbon nanojunction constructed by a graphene nanoflake (GNF) and zigzag-edged graphene nanoribbons (ZGNRs), bridged by the carbon atomic chains.