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Efficient Spin Injection into Graphene through a Tunnel Barrier: Overcoming the Spin-Conductance Mismatch

Qingyun Wu1, Lei Shen ((沈雷))2,1,*, Zhaoqiang Bai1, Minggang Zeng1, Ming Yang1, Zhigao Huang3, and Yuan Ping Feng1,†

  • 1Department of Physics, National University of Singapore, Singapore 117542, Singapore
  • 2Engineering Science Programme, Faculty of Engineering, National University of Singapore, Singapore 117579, Singapore
  • 3College of Physics and Energy, Fujian Normal University, Fuzhou 350007, People’s Republic of China

  • *shenlei@nus.edu.sg
  • †phyfyp@nus.edu.sg
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Phys. Rev. Applied 2, 044008 – Published 16 October, 2014

DOI: https://doi.org/10.1103/PhysRevApplied.2.044008

Abstract

Employing first-principles calculations, we investigate the efficiency of spin injection from a ferromagnetic electrode (Ni) into graphene and a possible enhancement by using a barrier between the electrode and graphene. Three types of barriers, h-BN, Cu(111), and graphite, of various thickness (0–3 layers) are considered, and the electrically biased conductance of the Ni/barrier/graphene junction is calculated. It is found that the minority-spin-transport channel of graphene can be strongly suppressed by the insulating h-BN barrier, resulting in a high spin-injection efficiency. On the other hand, the calculated spin-injection efficiencies of Ni/Cu/graphene and Ni/graphite/graphene junctions are low, due to the spin-conductance mismatch. Further examination of the electronic structure of the system reveals that the high spin-injection efficiency in the presence of a tunnel barrier is due to its asymmetric effects on the two spin states of graphene.

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Phys. Rev. Applied 2, 044008– Published 16 October, 2014
  • Received 30 May 2014

© 2014 American Physical Society

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