Antiferromagnetic-ferromagnetic transition in zigzag graphene nanoribbons induced by substitutional doping

Using first-principles calculations based on density functional theory,we show that the ground state of zigzag-edged graphene nanoribbons(ZGNRs)can be transformed from antiferromagnetic(AFM)order to ferromagnetic(FM)order by changing the substitutional sites of N or B dopants.This AFM–FM transition induced by substitutional sites is found to be a consequence of the competition between the edge and bulk states.The energy sequence of the edge and bulk states near the Fermi level is reversed in the AFM and FM configurations.When the dopant is substituted near the edge of the ribbon,the extra charge from the dopant is energetically favorable to occupy the edge states in AFM configuration.When the dopant is substituted near the center,the extra charge is energetically favorable to occupy the bulk states in FM configuration.Proper substrate with weak interaction is necessary to maintain the magnetic properties of the doped ZGNRs.Our study can serve as a guide to synthesize graphene nanostructures with stable FM order for future applications to spintronic devices.