Influence of the Field Strength and Direction on the Magnetic Phases of an Antiferromagnet with Uniaxial Anisotropy

Abstract

For a two-sublattice uniaxial Néel-type antiferromagnet, the stable spin configurations at the zero-temperature under an external magnetic field of arbitrary direction within a particular plane are studied in the nearest neighbor spin-coupling approximation. Particularly, the effects of single ionic anisotropy D -term and anisotropy in the exchange interactions on the magnetic phases are investigated. As a result, it has turned out that the antiferromagnetic state appears only for the external magnetic field along the easy axis of sublattice magnetization and shows a first-order phase transition to the canted-spin state for D < D 0 or directly to the ferromagnetic state for D ≧ D 0 where D 0 =0.5| J | z 0 with the exchange integral J and the number of nearest neighbors z 0 . For other field directions, no antiferromagnetic state appears and only the second-order phase transition between the canted-spin and ferromagnetic states occurs. The critical field as a function of external field direction has been calculated for several D -values.