Spin filter properties of armchair graphene nanoribbons with substitutional Fe atoms

Spin polarization in graphene nanoribbons functionalized with nitroxide

Fine-tuning of magnetic states via an understanding of spin injection on the edge of graphene nanoribbons should allow for greater flexibility of the design of graphene-based spintronics. On the basis of calculations, we predict that coupling constants of the exchange interaction in the series of nitroxide-functionalized ribbon compounds are antiferromagnetic across the ribbons with values 0.2-0.4 cm^-1 and ferromagnetic along the ribbon with absolute values from 0.05 to 0.07 cm^-1. Such interacting nitroxide groups induce spin polarization of the edge states of stable graphene nanoribbons. Graphical abstract Exchange coupling constants inducing spin polarization in graphene nanoribbons functionalized with nitroxides.

Strained zigzag graphene nanoribbon devices with vacancies as perfect spin filters

The transport properties of zigzag graphene nanoribbons (zGNRs) were studied by density functional theory (DFT) in conjunction with Green's function analysis. In particular, spin transport through a zGNR (12,0) device was investigated under the constraint of ferromagnetic coordination of the ribbon edges. Several configurations with two vacant sites in the edge and the bulk region of the zGNR device were derived from this system. For all structures, magnetocurrent ratios (MCRs) were recorded as a function of the bias as well as the amount of strain applied longitudinally to the devices. ZGNR devices with vacancies in the edge regime turn out to exhibit perfect spin-filter activity for well-defined choices of the strain and the bias, carrying completely polarized minority spin currents. In the alternative structure, characterized by vacancies in the bulk regime, spin currents with majority orientation prevail. With respect to both the sign and the size, the MCR is seen to depend sensitively on the device parameters, i.e., the vacancy locations, the bias, and the amount of strain. These results are interpreted in terms of density-of-states distributions, transmission spectra, and transmission operator eigenstates.