Magnetic Ordering in a Hexagonal Antiferromagnet

Abstract

The magnetic ordering in a hexagonal antiferromagnetic system with both the exchange anisotropy energy and the single-ion anisotropy energy is studied by using the molecular field approximation. It is shown that the magnetic moments in an ordered phase appearing at T ≤ T N form either a collinear structure with the moments parallel or antiparallel to the hexagonal axis or a triangular structure in the basal plane, and that an arrangement of the moments at T ∼0 shows a variety of structures. Thus, the system exhibits a variety of magnetic ordering processes as the temperature lowers. Our results may give a systematic explanation of anomalous ordering processes observed in recent experiments.