We investigate the effect of edge defects (vacancies) and impurities (substitutional dopants) on the robustness of spin-polarization in graphene nanoribbons (GNRs) with zigzag edges, using density-functional-theory calculations. We found that the stability

FIG.1:Isovaluesurfacesofchargedi erencebetweenthespin-upandspin-downstatesofthegroundstatescalculatedforthe(2.5,2.5)GNRatthreedi erentlinearvacancyconcentrationsontheedge:(a)0.034 A 1,(b)0.068 A 1,and(c)0.136 A 1.HalfofthesupercellinFig.1a,oneinFi.g1bandtwoinFig.1careshown.Theyellowandbluesurfacerepresentsspin-upand

1incase(a)andspin-downstate,respectively.Therangeofisovaluesissetat[-0.005:0.005]µBA

[-0.003:0.003]µB A 1incaseof(b)and(c).(d)-(f)Thesameas(a)-(c)forBimpurities.(g)Themagneticmomentperedgeatomonthetopedge,atthreevacancyconcentrationscorrespondingtothecaseof(a),(b)and(c),plusthecasewithoutvacancy.(h)Thesameas(g)forBimpurities.ations.Themagnetismcanalsobe”dead”locallyinbetweentwodefects(impurities)aslongastheyarecloserthanthethirdnearest-neighbor(NN)positions.ThespinsuppressioncorrelatescloselywiththereductionandremovalofedgestatesattheFermienergy.

OurcalculationsareperformedusingDFTpseudopotentialplane-wavemethodwithinthelocalspindensityapproximation[13].Theplanewavecut-o energyissetas450eV.Thestructureoptimizationhasbeenperformeduntiltheresidualatomicforcesarelessthan0.01eV/ A.WecalculatedGNRswithH-terminatedzigzagedgesoftwodi erentwidths,