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

Graphenenanoribbons(GNRs)haveattractedmuchrecentinterestbecauseoftheiruniqueelectronicpropertiesandpotentialfordeviceapplications[1,2,3,4,5,6,7,8,9,10,11].OfparticularinterestarethoseGNRswithzigzagedges,whichareshowntohaveaspin-polarizedgroundstate[4,5,8].Thespin-polarizationisoriginatedfromtheedgestatesthatintroduceahighdensityofstateattheFermienergy.Itcanbequalita-tivelyunderstoodintermsofStonermagnetismofspelectrons(inanalogytoconventionaldelectrons)occupyingaverynarrowedgebandtorenderaninstabilityofspin-bandsplitting

[12].Thespinsarefoundtobelocalizedontheribbonedges,withferromagneticcouplingwithineachedgeandantiferromagneticcouplingbetweenthetwoedges.

BecausethemagnetisminGNRsisresultedfromthehighlydegenerateedgestates,itmustrequireaperfectedgestructure.However,realsamplesofGNRs[9]areunlikelytohaveperfectedgesbutcontainstructuraldefectsandimpuritiesofforeignatomicspecies.Thus,oneimportantquestionishowrobustisthespinstateinpresenceofedgedefectsandimpurities.Theanswertothisquestionnotonlyisscienti callyinterestingtobetterunderstandthephysicalmechanismsofspin-polarizationinGNRs,butalsohaveimportanttechnologicallyimplicationsifGNRsaretoberealizedasanewclassofspintronicmaterials.Someexistingstudies[5]seemedtosuggestthatthespinsinGNRsarerobustagainstformationofedgedefectsatcertainconcentrations.However,inthisLetter,weshowthatthespinscanbecompletelyremovedbyedgedefectsorimpuritiesatconcentrationsaccessibleinrealsamples,whichrendersapracticaldi cultforrealizingspin-polarizationinGNRs.Wehaveperformedasystematicstudyofthestabilityanddegreeofspin-polarizationinGNRsasafunctionoftheconcentrationofedgedefectsandimpurities,using rst-principlesdensity-functional-theory(DFT)calculations,Wechosevacancyandsubstitutionalboron

(B)atom,astypicalexamplesofstructuraledgedefectandimpurity,respectively,sincevacanciesareexpectedtobethemostabundantdefectsinaroughenededgeandBatomsareacommonchoiceofelectronicdopants[6,7].Ourcalculationsshowthatthespiniscom-pletelysuppressedatthedefect(impurity)sites,whileitmaypreserveonthosesitesawayfromdefects(impurities)whenthedefect(impurity)concentrationislow.Thestabilityofthespinstateandits”average”magneticmomentdecreasescontinuouslywithincreasingdefect(impurity)concentration.Typically,independentofribbonwidth,thesystembe-comesnon-magneticatthecriticalconcentrationofoneedgedefect(impurity)per～10 A,aconcentrationshowntobeaccessibleinrealsamplesbasedonthermodynamicconsider-