  Recent experiments indicate room-temperature ferromagnetism in graphite like
materials. This paper offers an multiple spin state analysis to find out the
origine of ferromagnetism in case of nano meter size graphene molecule.First
principle density function theory calculation (DFT-GGA with 631-G basis set) is
applied to nano meter size asymmetric graphene fifteen molecules. Major results
are,(1) Dihydrogenated zigzag edge molecule like C64H27 show that the most
stable (lowest molecular energy) spin state is the highest one as Sz=5/2.
Examples for spin density map of Sz=1/2,3/2 and 5/2 is shown in Fig.1. In other
molecules like C56H24, C64H25, C64H22 and C64H23 also show the highest spin
state most stable as shown in Fig.2. Energy difference between most stable spin
state and next one overcome temperature difference 1000K,which suggests a
stability of room temperature ferromagnetism. (2) Radical carbon zigzag edge
molecules are also analysed. As illustrated in Fig.3, in every five molecule,
also the highest spin state is most stable. (3) In contrast, nitrogen
substituted molecules like C59N5H22, C61N3H22 etc. show opposite result,that
is, the lowest spin state is most stable as shown in Fig.4. There are following
three key issues to bring those results. (A) Edge specified localized spin
arrangement. (B) Up-Up (also Down-Down) complex spin pairs inside of molecule.
(C) Optimized atom position rearrangement depend on the spin state. Detailed
mechanism will be discussed in the Symposium. Multiple spin state analysis is
very useful to design carbon based ferro-magnet and also to design new
spintronic devices.
