▎ 摘　　要

We have measured the magnetoresistance of freely suspended high-mobility bilayer graphene. For magnetic fields B > 1 T we observe the opening of a field-induced gap at the charge neutrality point characterized by a diverging resistance. For higher fields the eightfold degenerated lowest Landau level lifts completely. Both the sequence of this symmetry breaking and the strong transition of the gap-size point to a ferromagnetic nature of the insulating phase developing at the charge neutrality point.