Spin-Ordered States in Multilayer Massless Dirac Fermion Systems

We investigate the spin-ordered states in multilayer massless Dirac fermion systems under magnetic fields, in which the intralayer interaction is ferromagnetic owing to the exchange interaction, while the interlayer interaction is antiferromagnetic arising from the interlayer hopping and the on-site Coulomb repulsion. The possible spin-ordered states are examined within the mean field theory, and we apply it to alpha-(BEDT-TTF)(2)I-3, which is a multilayer massless Dirac fermion system under pressure. In the weak interlayer coupling regime the system exhibits a ferromagnetically spin-ordered state with the effective Zeeman g-factor less than two contrasting to that observed in the single-layer graphene.