Generation of pure spin current in graphene nanoribbons with continous antidots

Abstract

Spin caloritronics, which combines the characteristics of thermoelectronics with the characteristics of spintronics, has a wide range of promising applications in high-speed and low-dissipation devices. In this paper, according to the density functional theory combined with nonequilibrium Green’s function method, we propose a scheme for generating pure spin current with spin dependent Seebeck effect in the zigzag-edged graphene nanoribbons by introducing continuous antidots (hexagonal defects). Specifically, by creating an antidot at one edge of the nanoribbon, an X-shape transmission spectrum around the Fermi level is formed, which results from the disrupted edge of the nanoribbon. The mechanism is well explained by the cooperation between the varying localization features of the eigenstates around the Fermi level for the unit cell and the scattering states at the Fermi level for the device. Therefore, the electrons of the two spin channels flow in the opposite directions under a temperature gradient, generating the spin current and charge current. By slightly tuning the chemical potential of the device, the charge current can be zero, while the spin current is not equal to zero. With the increase of adjacent antidot number along the width of the nanoribbons, the structures are more disrupted, thus promoting the pure spin current due to the increase of the spin Seebeck coefficient. However, for zigzag graphene nanoribbons with <i>W</i> zigzag carbon chains, the pure spin current decreases when the number of the antidots are more than (<i>W</i>/2–1), which results from the decrease of the spin conductance. So, the maximum pure spin current can be obtained when the number of the continuous antidots introduced along the width of nanoribbons reaches (<i>W</i>/2–1). These findings indicate a novel strategy for thermally generating the spin current by introducing continuous antidots along the nanoribbon bandwidth in zigzag graphene nanoribbons and will be greatly instructive in designing the graphene spintronic devices.