skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Spin and charge thermopower effects in the ferromagnetic graphene junction

Abstract

Using wave function matching approach and employing the Landauer-Buttiker formula, a ferromagnetic graphene junction with temperature gradient across the system is studied. We calculate the thermally induced charge and spin current as well as the thermoelectric voltage (Seebeck effect) in the linear and nonlinear regimes. Our calculation revealed that due to the electron-hole symmetry, the charge Seebeck coefficient is, for an undoped magnetic graphene, an odd function of chemical potential while the spin Seebeck coefficient is an even function regardless of the temperature gradient and junction length. We have also found with an accurate tuning external parameter, namely, the exchange filed and gate voltage, the temperature gradient across the junction drives a pure spin current without accompanying the charge current. Another important characteristic of thermoelectric transport, thermally induced current in the nonlinear regime, is examined. It would be our main finding that with increasing thermal gradient applied to the junction the spin and charge thermovoltages decrease and even become zero for non zero temperature bias.

Authors:
 [1];  [2];  [3]
  1. Department of Physics, Sari Branch, Islamic Azad University, Sari (Iran, Islamic Republic of)
  2. (IBS), Daejeon (Korea, Republic of)
  3. Center for Theoretical Physics of Complex Systems, Institute for Basic Science (IBS), Daejeon (Korea, Republic of)
Publication Date:
OSTI Identifier:
22598878
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ELECTRIC POTENTIAL; ELECTRONS; FERROMAGNETIC MATERIALS; GRAPHENE; HOLES; JOINTS; LENGTH; NONLINEAR PROBLEMS; SEEBECK EFFECT; SPIN; TEMPERATURE GRADIENTS; WAVE FUNCTIONS

Citation Formats

Vahedi, Javad, E-mail: javahedi@gmail.com, Center for Theoretical Physics of Complex Systems, Institute for Basic Science, and Barimani, Fattaneh. Spin and charge thermopower effects in the ferromagnetic graphene junction. United States: N. p., 2016. Web. doi:10.1063/1.4961093.
Vahedi, Javad, E-mail: javahedi@gmail.com, Center for Theoretical Physics of Complex Systems, Institute for Basic Science, & Barimani, Fattaneh. Spin and charge thermopower effects in the ferromagnetic graphene junction. United States. doi:10.1063/1.4961093.
Vahedi, Javad, E-mail: javahedi@gmail.com, Center for Theoretical Physics of Complex Systems, Institute for Basic Science, and Barimani, Fattaneh. 2016. "Spin and charge thermopower effects in the ferromagnetic graphene junction". United States. doi:10.1063/1.4961093.
@article{osti_22598878,
title = {Spin and charge thermopower effects in the ferromagnetic graphene junction},
author = {Vahedi, Javad, E-mail: javahedi@gmail.com and Center for Theoretical Physics of Complex Systems, Institute for Basic Science and Barimani, Fattaneh},
abstractNote = {Using wave function matching approach and employing the Landauer-Buttiker formula, a ferromagnetic graphene junction with temperature gradient across the system is studied. We calculate the thermally induced charge and spin current as well as the thermoelectric voltage (Seebeck effect) in the linear and nonlinear regimes. Our calculation revealed that due to the electron-hole symmetry, the charge Seebeck coefficient is, for an undoped magnetic graphene, an odd function of chemical potential while the spin Seebeck coefficient is an even function regardless of the temperature gradient and junction length. We have also found with an accurate tuning external parameter, namely, the exchange filed and gate voltage, the temperature gradient across the junction drives a pure spin current without accompanying the charge current. Another important characteristic of thermoelectric transport, thermally induced current in the nonlinear regime, is examined. It would be our main finding that with increasing thermal gradient applied to the junction the spin and charge thermovoltages decrease and even become zero for non zero temperature bias.},
doi = {10.1063/1.4961093},
journal = {Journal of Applied Physics},
number = 8,
volume = 120,
place = {United States},
year = 2016,
month = 8
}
  • We theoretically investigate spin-dependent Seebeck effects for a system consisting of a narrow graphene nanoribbon (GNR) contacted to square lattice ferromagnetic (FM) electrodes with noncollinear magnetic moments. Both zigzag-edge graphene nanoribbons (ZGNRs) and armchair-edge graphene nanoribbons (AGNRs) were considered. Compared with our previous work with two-dimensional honeycomb-lattice FM leads, a more realistic model of two-dimensional square-lattice FM electrodes is adopted here. Using the nonequilibrium Green's function method combining with the tight-binding Hamiltonian, it is demonstrated that both the charge Seebeck coefficient S{sub C} and the spin-dependent Seebeck coefficient S{sub S} strongly depend on the geometrical contact between the GNR andmore » the leads. In our previous work, S{sub C} for a semiconducting 15-AGNR system near the Dirac point is two orders of magnitude larger than that of a metallic 17-AGNR system. However, S{sub C} is the same order of magnitude for both metallic 17-AGNR and semiconducting 15-AGNR systems in the present paper because of the lack of a transmission energy gap for the 15-AGNR system. Furthermore, the spin-dependent Seebeck coefficient S{sub S} for the systems with 20-ZGNR, 17-AGNR, and 15-AGNR is of the same order of magnitude and its maximum absolute value can reach 8 μV/K. The spin-dependent Seebeck effects are not very pronounced because the transmission coefficient weakly depends on spin orientation. Moreover, the spin-dependent Seebeck coefficient is further suppressed with increasing angle between the relative alignments of magnetization directions of the two leads. Additionally, the spin-dependent Seebeck coefficient can be strongly suppressed for larger disorder strength. The results obtained here may provide valuable theoretical guidance in the experimental design of heat spintronic devices.« less
  • No abstract prepared.
  • We investigate thermoelectric effects in quantum well systems. Using the scattering approach for coherent conductors, we calculate the thermocurrent and thermopower both in the spin-degenerate case and in the presence of giant Zeeman splitting due to magnetic interactions in the quantum well. We find that the thermoelectric current at linear response is maximal when the well level is aligned with the Fermi energy and is robust against thermal variations. Furthermore, our results show a spin voltage generation in response to the applied thermal bias, giving rise to large spin Seebeck effects tunable with external magnetic fields, quantum well tailoring, andmore » background temperature.« less
  • We propose and demonstrate that a EuO-induced and top-gated graphene ferromagnetic junction can be simultaneously operated as a spin filter and a spin valve. We attribute such a remarkable result to a coexistence of a half-metal band and a common energy gap for opposite spins in ferromagnetic graphene. We show that both the spin filter and the spin valve can be effectively controlled by a back gate voltage, and they survive for practical metal contacts and finite temperature. Specifically, larger single spin currents and on-state currents can be reached with contacts with work functions similar to graphene, and the spinmore » filter can operate at higher temperature than the spin valve.« less