Abstract
High-field ESR measurements of the novel Mn substance Bi3Mn4O12(NO3), which is a model substance of S=3/2 honeycomb lattice antiferromagnet, have been performed using the pulsed magnetic field up to 16 T. No resonance shift and the gapless behavior are observed in the temperature dependence measurements. Although, very strong antiferromagnetic interactions are expected from the Weiss temperature, there is no evidence of the long-range ordering down to 1.9 K from the magnetic susceptibility, the specific heat and the ESR measurements. Therefore, the existence of the frustration effect in Bi3Mn4O12(NO3) is strongly suggested in spite of the honeycomb lattice structure.