A Microscopic Theory of the Phase Transition in RbFeCl3-Type Hexagonal Antiferromagnets: Effects of the Dipole-Dipole Interaction

Effects of the dipole-dipole (DD) interaction on the phase transition in RbFeCl 3 -type hexagonal antiferromagnets are studied microscopically. The magnetic phase diagram of two typical cases is determined by the molecular-field approximation (MFA): CsNiF 3 (DD coupling\({}\)interchain exchange coupling) and RbFeCl 3 (DD coupling≪interchain exhcange coupling). We show that incommensurate (IC) phases are common in these systems. Even in CsNiF 3 , where no IC phase appears in weak fields, an IC fan structure can appear in the high field region if the magnetic field is applied along a suitable direction. As an attempt to improve the MFA the magnetic phase diagram of RbFeCl 3 is determined by making use of the inverse susceptibility tensor calculated by the dynamical correlated-effective-field approximation (DCEFA).