Spin-polarized transport in hydrogen-passivated graphene and silicene nanoribbons with magnetic transition-metal substituents

Exfoliable and self-healable two-dimensional materials from wurtzite zinc chalcogenides as building blocks of nanodevices

With the advent of graphene, two-dimensional (2D) materials have emerged as promising candidates for next-generation electronic and optoelectronic applications. The most anticipated 2D materials have been synthesized and exploited for novel applications. Multilayered zinc chalcogenides (ZnX) are the best precursors for obtaining atomic layer two-dimensional materials by exfoliation. Therefore, we carry out a detailed density functional theory-based study to achieve an exfoliation process of ZnX non-van der Waals sheets by straining and provide a microscopic understanding of the ferroelectric, optic, and spin behaviors of ZnX systems and the corresponding self-healable two-dimensional ZnX devices. The results revealed that 2D ZnX sheets can be obtained when strain is 14% for ZnS and ZnSe, and the peak values of exfoliation energy have a similar order of magnitude to those of traditional 2D materials, indicating the possibility of obtaining 2D ZnX monolayers. For intrinsic 2D ferroelectric materials with in-plane electric polarization, the direction of ZnX sheets can be reversed using an electric field with an energy barrier of ∼0.175 eV per atom for ZnSe, offering a promising functional basis for their application in ferroelectric nanodevices. The first absorption of photons for polarization perpendicular to the monolayer plane occurs in a high energy range of photons, facilitating their application in LEDs. The spin splitting in non-centrosymmetric ZnX crystals exhibits a Rashba spin-texture according to first-principles calculations. The self-healable two-dimensional nanodevices have a smooth curve from -0.5 to 0.5 eV. This work indicates the potential value of non-van der Waals ZnX 2D materials for their application in photoelectric and spintronic nanodevices.

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.