Large suppression of spin-relaxation rate in graphene nanoribbons in the presence of magnetic impurities

Abstract

Achievement of low spin-relaxation rate is an important goal for spintronics development. We study the spin-relaxation rate arising from a low concentration of magnetic impurities in armchair graphene nanoribbons (AGNR). Large suppression in the spin-relaxation rate, exhibited as dip structures, is found when the Fermi energy approaches a subband band edge. This suppression originated from the quasi-one-dimensional density of states and is manifested via the singular features in the AGNR same-site Green's function ${G}_{\mathcal{II}}$, where $\mathcal{I}$ denotes site locations of magnetic impurities. Analytic analysis of the spin-relaxation rate in the close vicinity of a subband band edge is performed to further reveal the physical nature of the suppression. The robustness of the suppression feature in the spin-relaxation rate is demonstrated by systematically increasing the number of magnetic impurities involved in a coherent multiple scattering with the electrons. Major peaks in the spin-relaxation rate are analyzed in light of their connection with spin-flipped resonances. Competition between magnetic impurities with similar resonance energies is found to lead to suppression in the spin-relaxation rate. Our calculations have taken into account the hydrogen-passivation effects at the AGNR edges when the hopping constant between edge carbons is modified.