Thermal spin transport properties in a hybrid structure of single-walled carbon nanotubes and zigzag-edge boron nitride nanoribbons

Abstract

The spin caloritronics device, because of the characteristics of spintronics and thermoelectronics, plays an important role in human sustainable development. A lot of spin caloritronic devices based carbon materials (such as graphene nanoribbons, carbon nanotubes) have been reported. However, there are few studies of the thermal spin transport properties in a hybrid structure of single-walled carbon nanotubes and zigzag-edge BN nanoribbons, and the thermal spin transport mechanism of this structure is still unclear. In this paper, using the nonequilibrium Green’s function (NEGF) combined with the first principle calculations, the electronic structures and the thermal spin transport properties of the zigzag edge BN nanoribbons functionalized single-walled carbon nanotubes are studied. It is shown that the ZBNRs-N-(6, 6)SWCNT is a half-metal, while the <i>n</i>ZBNRs-N-(6, 6)SWCNT are magnetic metals (<i>n</i> = 2−8), and the <i>n</i>ZBNRs-B-(6, 6)SWCNT are bipolar magnetic semiconductors (<i>n</i> = 1−8). The 4ZBNRs-N-(4, 4)SWCNT and 4ZBNRs-B-(4, 4)SWCNT are half-metals, while the 4ZBNRs-B-(<i>m</i>, <i>m</i>)SWCNT (<i>m</i> = 5−9)are magnetic metals, and the 4ZBNRs-N-(<i>m</i>, <i>m</i>)SWCNT (<i>m</i> = 5−9) are bipolar magnetic semiconductors. Then, some novel spin caloritronicdevices are designed based on <i>n</i>ZBNRs-N-(6, 6)SWCNT and <i>n</i>ZBNRs-B-(6, 6)SWCNT (<i>n</i> = 1, 8). For the ZBNRs-B-(6, 6)SWCNT, when the temperature of the left electrode is increased above a critical value, the thermal spin-up current then increases remarkably from zero. Meanwhile the thermal spin-down current remains approximately equal to zero in the entire temperature region, thus indicating the formation of a thermal spin filter. For the 8ZBNRs-N-(6, 6)SWCNT and <i>n</i>ZBNRs-B-(6, 6)SWCNT (<i>n</i> = 1, 8), when a temperature gradient is produced between two electrodes, the spin-up and spin-down currents are driven in the opposite directions, which indicates that the spin-dependent Seebeck effect (SDSE) appears. In order to obtain the fundamental mechanism of thermal spin filter effect and SDSE, the Landauer-Büttiker formalism is adopted. It is found that the currents (<i>I</i><sub>up</sub> and <i>I</i><sub>dn</sub>) mainly depend on two factors: 1)the transport coefficient; 2) the difference between the Fermi-Dirac distributions of the left and right electrode. Additionally, the electron current <i>I</i><sub>e</sub> and the hole current <i>I</i><sub>h</sub> will be generated when a temperature gradient is produced between the left and right lead. Furthermore, the <i>I</i><sub>up</sub> and <i>I</i><sub>dn</sub> have the opposite directions for the spin up transmission peaksbelow the Fermi level while they have the opposite directions for the spin down transmission peaks above the Fermi level in the transmission spectrum, which demonstrates the presence of the SDSE in the 8ZBNRs-B-(6, 6)SWCNT and <i>n</i>ZBNRs-N-(6, 6)SWCNT (<i>n</i> = 1, 8). Finally, the results indicate that <i>n</i>ZBNR-N-(<i>m</i>, <i>m</i>)SWCNT and <i>n</i>ZBNR-B-(<i>m</i>, <i>m</i>)SWCNT can have potential applications in thermospin electronic devices.