State diagram of an antiferromagnet with a predominant Dzyaloshinskii interaction

Abstract

A phase diagram in the variables Hz, Hy is constructed for an easy-axis tetragonal antiferromagnet with a predominant Dzyaloshinskii interaction. On this diagram the lines of second-order phase transitions between the canted phase and a phase in which the antiferromagnetic vector l is perpendicular to the easy axis begin and end at the fields of spin-flip transitions (i.e., at the exchange field). These lines of second-order phase transitions have the feature that each of them has two tricritical points, at which a transition occurs to a line of first-order phase transitions. The critical angle between the magnetic field direction and the basal plane, within which a first-order phase transition occurs, is determined. The value of this angle is temperature dependent. The position of the tricritical point on the Hz–Hy (or, equivalently, the Hz–Hy phase diagram is also temperature dependent.