Gate-voltage controlled spin pumping effects: spin injection from YIG and Co into metal and graphene based 2 D materials

Spin current injection into nonmagnetic metals, semiconductors and oxides is crucial component of spintronics. The spin pumping mechanism free from the impedance mismatch is a promising way to inject spin current into nonmagnetic materials [1]. Here we present theory of spin current injected into non-magnetic films which arises from magnetization precession. We apply this theory to two cases (i) insulating yttrium iron garnet ferromagnet/nonmagnetic metal interfaces and (ii) hcp-Co/single layer graphene interface. The electron transport calculations are based on the non-equilibrium Green Function formalism within the tight binding Hamiltonian model [2]. We show that magnitude of the pumped spin current can be efficiently controlled by the gate voltage. \\[4pt] [1] K. Ando, S. Takahashi, J. Ieda, H. Kurebayashi, T. Trypiniotis, C. H. W. Barnes, S. Maekawa and E. Saitoh, Nature Mater. \textbf{10}, 655 (2011).\\[0pt] [2] S.-H. Chen, C.-R. Chang, J. Q. Xiao and B. K. Nikolic, Phys. Rev. B \textbf{79}, 054424 (2009).