Asymmetric graphene model applied to graphite-like carbon-based ferromagnetism

摘要

Several experiments have recently found room-temperature ferromagnetism ingraphite-like carbon based materials. This paper offers a model explaining suchferromagnetism by using an asymmetric nano-graphene. Our first typical model isC48H24 graphene molecule, which has three dihydrogenated (-CH2) zigzag edges.There are several multiple spin states competing for stable minimum energy inthe same atomic topology. Both molecular orbital and density function theorymethods indicate that the quartet state(S=3/2) is more stable than that ofdoublet (S=1/2), which means that larger saturation magnetization will beachieved. We also enhanced this molecule to an infinite length ribbon havingmany (-CH2) edges. Similar results were obtained where the highest spin statewas more stable than lower spin state. In contrast, a nitrogen substituted(-NH) molecule C45N3H21 demonstrated opposite results. that is, the lowest spinstate(S=1/2) is more stable than that of highest one(S=3/2), which arises fromthe slight change in atom position.