# Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads

## Abstract

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 and 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 notmore »

- Authors:

- Department of Physics, Shaoyang University, Shaoyang 422001 (China)
- Department of Physics and Key Laboratory for Low-Dimensional Structures and Quantum Manipulation (Ministry of Education), Hunan Normal University, Changsha 410081 (China)
- Hunan Key Laboratory for Micro-Nano Energy Materials and Device and Department of Physics, Xiangtan University, Xiangtan 411105 (China)

- Publication Date:

- OSTI Identifier:
- 22399256

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 10; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COMPARATIVE EVALUATIONS; ELECTRODES; ENERGY GAP; FERROMAGNETIC MATERIALS; FERROMAGNETISM; GRAPHENE; HAMILTONIANS; MAGNETIC MOMENTS; MAGNETIZATION; NANOSTRUCTURES; SEMICONDUCTOR MATERIALS; SPIN; SPIN ORIENTATION; TETRAGONAL LATTICES; TWO-DIMENSIONAL CALCULATIONS; TWO-DIMENSIONAL SYSTEMS

### Citation Formats

```
Zhou, Benhu, E-mail: zhoubenhu@163.com, Zeng, Yangsu, Zhou, Benliang, Zhou, Guanghui, E-mail: ghzhou@hunnu.edu.cn, and Ouyang, Tao.
```*Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads*. United States: N. p., 2015.
Web. doi:10.1063/1.4914486.

```
Zhou, Benhu, E-mail: zhoubenhu@163.com, Zeng, Yangsu, Zhou, Benliang, Zhou, Guanghui, E-mail: ghzhou@hunnu.edu.cn, & Ouyang, Tao.
```*Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads*. United States. doi:10.1063/1.4914486.

```
Zhou, Benhu, E-mail: zhoubenhu@163.com, Zeng, Yangsu, Zhou, Benliang, Zhou, Guanghui, E-mail: ghzhou@hunnu.edu.cn, and Ouyang, Tao. Sat .
"Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads". United States.
doi:10.1063/1.4914486.
```

```
@article{osti_22399256,
```

title = {Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads},

author = {Zhou, Benhu, E-mail: zhoubenhu@163.com and Zeng, Yangsu and Zhou, Benliang and Zhou, Guanghui, E-mail: ghzhou@hunnu.edu.cn and Ouyang, Tao},

abstractNote = {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 and 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.},

doi = {10.1063/1.4914486},

journal = {Journal of Applied Physics},

number = 10,

volume = 117,

place = {United States},

year = {Sat Mar 14 00:00:00 EDT 2015},

month = {Sat Mar 14 00:00:00 EDT 2015}

}