Low Temperture Heat Capacity of Nanographene to Study Edge-State Spin

Graphene is two dimensional honeycomb carbon sheets which have localized spin in unique zigzag edge. In the nanometer-sized graphene, the edge region is not negligible. So the localized spin much contributes to the electronic structure. Especially the localized edge-state spin coupled with the itinerant π carriers. We performed heat capacity study of nanometer-sized graphene samples prepared by detonating nanodiamond. The lattice heat capacity was found to be in proportion to T 2 down to 2 K because of the two dimensional of graphene sheets. In low temperature region, a Schottky anomaly due to localized spins was observed, even under zero-magnetic field. It indicates that localized spin feels internal magnetic field. Coupling of localized edge-state with itinerant π carriers is interesting possibility of electronic structure of graphene. The electronic heat capacity coefficient is estimated as 760 µJ K−2 C-mol−1 for one sample studied. It is suggested that the itinerant electrons coupled with the localized spin in zigzag edges.

(by Y. Horie & Y. Nakazawa)

Fig. 1.Two types of edge structures of grapheme (○zigzag, ◊armchair)

Fig. 2. Cp vs T curves for 4 types of graphitic samples. Nanographene has larger lattice heat capacity than graphite.