The Study Of Spin Caloritronics On Two Dimensional Materials Based On Silicon-carbide And Silicene Nanoribbons

Spin caloritronics with a combination of spintronics and thermoelectrics has potential applications in future information science and open a new direction towards the future multi-functional materials and thermoelectric waste heat recovery technologies. Based on density functional theory combined with nonequilibrium Green's function method, we have investigated the thermal spin transport properties by surveying several spin caloritronics devices. Our main results are listed as follows in details.Firstly, we study the thermal spin transport through a zigzag silicon carbide nanoribbon(ZSiCNR), which is a heterojunction consisting of left electrode terminated with 4-ZSiCNR-2H1 H as the source and right electrode terminated with 4-ZSiCNR-1H1 H as the drain. Our results show that when the temperature difference between the source and the drain increases over a critical value, the thermal-induced spin-down current increases remarkably, while the thermal-induced spin-up current keeps zero nearly, indicating that a perfect thermal spin filter together with a perfect spin switcher is produced by temperature difference instead of external electrical bias. Furthermore, the thermal spin current performs a usual negative differential resistance effect and quantum oscillation behavior. Thus, the zigzag SiC nanoribbon proposed by us can be designed as a highly-efficient spin caloritronics device with multiple functionalities.Secondly, we study the transport properties of a new spin caloritronics device based on a zigzag silicene nanoribbon(ZSiNRs) heterojunction composed of single-hydrogenterminated ZSiNR in left electrode and double-hydrogen-terminated ZSi NRs in right electrode. We first calculate the thermal spin-dependent transport properties in the(4-ZSi NR-H)/(4-ZSiNR-H2) heterojunction. We find that, by applying temperature difference between the source and the drain, spin-up and spin-down currents are driven and flow just in opposite directions, while the total charge current is nearly zero in the total-temperature region, which supports that a perfect Spin-Seebeck effect(SSE) emerges. We realize the giant magnetoresistance effect in the heterojunction by regulating external magnetic field. Meanwhile, we also study the spin caloritronics of the(N-ZSiNR-H)/(N-ZSiNR-H2) heterojunctions with different width N. For even-N ZSi NRs, the spin-up current and the spin-down current are almost symmetrical with each other about the zero-current axis, indicating that the magnitudes of the spin-dependent currents are neatly equivalent. Thus, the total charge current of even-N ZSiNRs is nearly zero in some critical temperatures, greatly reducing energy dissipation and benefiting to potential applications in the spin caloritronics devices. However, for odd-N ZSiNRs, this symmetry is broken, due to the fact that the charge current is large and exhibites rich physical properties. Moreover, we find an effective approach to obtain pure spin current by applying gate voltage in odd-N ZSiNRs. In addition, we can also realize the adjustment about the thermoelectric rectification(TR) and the negative differential thermal resistance(NDTR) by in these heterojunctions. Finally, we find that the Spin-Seebeck Diode effect appear in the these ZSiNR heterojunctions, paving the way for silicene-based spin caloritronics devices.