Spin caloritronics in spin semiconducting armchair graphene nanoribbons

We designed a spin-caloritronics device based on armchair graphene nanoribbons (AGNRs). We theoretically show that a trapezoidal-shaped graphene flake consisting of four zigzag edges bridged between two AGNRs becomes a spin semiconductor with a tunable spin-dependent transmission gap. The results indicate that the appearance of spin semiconducting properties with spin-dependent localized transmission peaks around the Fermi level could produce the spin-caloritronics effects of AGNRs. Interestingly, the values of the spin Seebeck coefficient S-S are comparable to values obtained for zigzag graphene nanoribbons, and also S-S sensitively increases as the transmission gap increases. Furthermore, by engineering the position and orientation of a triangular antidot only in the scattering region, both S-S and the spin figure of merit could be separately enhanced at room temperature.