Enhancement of thermospin effect in germanene based normal/ferromagnetic stub/normal junction

Abstract

Spin thermoelectric effects in ferromagnetic (FM) germanene are theoretically investigated by using the nonequilibrium Green's function method. It is found that the spin Seebeck effect can be generated by temperature bias ΔT when a FM germanene is considered in the central region. However, the obtained spin resolved Seebeck coefficients is quite low with maximum value of Sσ≃700μV/K. The spin Seebeck effect is shown to increase enormously in different energy states with the assistance of electric field or stub structure. By modulating the geometric parameters of stub, the spin thermopower Ss has distinct peak values in the bulk states. Moreover, varying the Fermi energy within the bulk gap by the gate, Ss can be significantly enhanced by increasing the strength of electric field. The spin thermopower obtained by each method is predicted to be 2500μV/K, which is more than 300% larger relative to the case without electric field or stub. In addition, the magnitude and sign of spin thermopower can be manipulated by adjusting the Fermi energy. The results show that such FM germanene stub device exhibits much better thermoelectric performance and may be used as a wide energy range tunable spin thermoelectric generator.