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Ferromagnetic Order Analysis of Fe- and FeO-modified Graphene-nano-ribbon

Graphene-nano-ribbon (GNR) is very attractive for ultra-high density spintronics devices. For checking a capability of self-induced ferromagnetic order, Fe- and FeO-modified GNR were analyzed based on the density functional theory. Model unit cells were [C32H2Fe2] and [C32H2Fe2O2]. Calculated results show the most stable spin state to be Sz=8/2 in [C32H2Fe2], whereas Sz=6/2 in [C32H2Fe2O2]. Magnetic moment M of Fe in [C32H2Fe2] was 3.65μB, which could be explained based on the Hund-rule considering donated charge to carbon to be M*=3.67μB . There is a capability of ferromagnetic Fe spin array through an interaction with carbon π-conjugated spin system. There shows a long-range super-exchange order in [C32H2Fe2O2]. Optimized atomic configuration gave the typical 90 degree super-exchange coupling between Fe-3d and O-2p orbit. Magnetic moment of Fe by DFT was 2.58μB, whereas super-exchange model considering donated charge to oxygen gave an estimated magnetic moment to be 2.60μB. Sign of magnetic moment of Fe and O are all up-spin each other. We could expect ferromagnetic long-range-order. Band structure was analyzed in FeO-modified case, which suggested half-metal like behavior. We can expect several spintronics applications as like a spin filter.