  Nanographite systems, where graphene sheets of the orders of the nanometer
size are stacked, show novel magnetic properties, such as, spin-glass like
behaviors and the change of ESR line widths in the course of gas adsorptions.
We theoretically investigate stacking effects in the zigzag nanographite sheets
by using a tight binding model with the Hubbard-like onsite interactions. We
find a remarkable difference in the magnetic properties between the simple A-A
and A-B type stackings. For the simple stacking, there are not magnetic
solutions. For the A-B stacking, we find antiferromagnetic solutions for strong
onsite repulsions. The local magnetic moments tend to exist at the edge sites
in each layer due to the large amplitude of wavefunctions at these sites. We
study variations between the A-A and A-B stackings to find that the magnetism
between the two stackings experiences the first order phase transition. The
effect of the interlayer distance is also discussed.
