Abstract
The main contribution of this paper is to study the spin caloritronic effects in defected graphene/silicene nanoribbon (GSNR) junctions. Each step-like GSNR is subjected to the ferromagnetic exchange and local external electric fields, and their responses are determined using the nonequilibrium Green’s function (NEGF) approach. To further study the thermoelectric (TE) properties of the GSNRs, three defect arrangements of divacancies (DVs) are also considered for a larger system, and their responses are re-evaluated. The results demonstrate that the defected GSNRs with the DVs can provide an almost perfect thermal spin filtering effect (SFE), and spin switching. A negative differential thermoelectric resistance (NDTR) effect and high spin polarization efficiency (SPE) larger than 99.99% are obtained. The system with the DV defects can show a large spin-dependent Seebeck coefficient, equal to Ss ⁓ 1.2 mV/K, which is relatively large and acceptable. Appropriate thermal and electronic properties of the GSNRs can also be obtained by tuning up the DV orientation in the device region. Accordingly, the step-like GSNRs can be employed to produce high efficiency spin caloritronic devices with various features in practical applications.
Highlights
The main contribution of this paper is to study the spin caloritronic effects in defected graphene/ silicene nanoribbon (GSNR) junctions
This paper numerically investigates the thermoelectric properties of parallel step-like GSNRs because: (1) the nanoribbons can satisfactorily show thermoelectric performance compared to their corresponding 2D structures[72] (2) the step-like nanostructures can provide some unusual thermal and electrical transport properties for the asymmetric shape of nanoribbons[62] (3) the hybrid type of nanostructures can often provide superior thermoelectric properties compared to the similar materials with the single nanostructures[32], and (4) the defected nanostructures can provide different thermoelectric properties of the nanoribbons
The divacancy effects were considered in the studied cases using the pentagon–octagon pentagon (5–8–5) type model
Summary
Three different parallel step-like GSNR junctions are introduced using semi-infinite metallic AGNRs with different widths of the left and right leads, and a ZSNR in the central region[43,77]. Where HL, HR, and HC are the Hamiltonian matrices of the isolated left electrode, right electrode, and the central region, respectively These submatrices can be determined by using Eqs. In which tR(L) and tC are the hopping energies for the nearest-neighbor interactions in the right (left) lead, and the central region, respectively. In this ci†α ( ciα ) denotes the fermion creation study, 2.66 and (annihilation). The electric and ferromagnetic exchange fields are assumed to be 0.082 V/Å and 0.162 eV, respectively, and perpendicularly applied to the central region of the hybrid GSNRs. The effects of inhomogeneous transverse electric fields EYS = 0.917 V/Å and EYG = 0.680 V/Å are considered. Based on the Landauer-Büttiker formula, the spin-dependent current can be obtained by[95]:
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