Spin-Dependent Electronic and Thermoelectric Transport Properties for a Sawtoothlike Graphene Nanoribbon Coupled to Two Ferromagnetic Leads

Abstract

The spin-dependent electronic transport and thermoelectric properties for a sawtoothlike graphene nanoribbon between two ferromagnetic leads with parallel or antiparallel magnetic moments are investigated theoretically. Both Christmas-tree graphene nanoribbon and tree-saw graphene nanoribbon have been considered to exemplify the effect of the chirality. By using ab initio calculations combined with a non-equilibrium Green’s function method, we obtain the important result that these sawtoothlike graphene nanoribbon junctions, regardless of their chirality, can exhibit giant charge and spin Seebeck coefficients as well as high thermoelectric efficiency at room temperature by putting ferromagnetic stripes or magnetic fields on the nanoribbons. Specifically, large $$|S_\mathrm{C}|\,(\sim 5.8~\hbox {mV/K})$$, $$|S_\mathrm{S}|(\sim 1.8~\hbox {mV/K})$$, charge figure of merit $$ZT_\mathrm{C}$$ and spin figure of merit $$ZT_\mathrm{S}(\sim 20)$$ were found in these sawtoothlike graphene nanoribbon junctions. In addition, negative differential resistance and spin filtering were also realized in these sawtoothlike graphene nanoribbon junctions. The maximum of spin filtering efficiency can be up to 100%. Our studies suggest that sawtoothlike graphene nanoribbon junctions are suitable for use as highly efficient spin caloritronics at room temperature.