The magnetic structure of ${\mathrm{CsNiCl}}_3$ is studied by using a phenomenological model free energy and shown to undergo two phase transitions. The first of these corresponds to the ordering of the Ni spins along the c axis and the second is to a phase in which the basal-plane component also becomes ordered. A small antiferromagnetic ordering (with modulation vector ${\mathrm{c}}^{\mathrm{*}}$) is predicted to coexist with the fundamental structure characterized by the wave vector ${\mathrm{Q}=(1/3(\mathrm{a}}^{\mathrm{*}}$${+\mathrm{b}}^{\mathrm{*}}$${)+\mathrm{c}}^{\mathrm{*}}$. .AE

• Received 30 March 1987

DOI:https://doi.org/10.1103/PhysRevB.36.3830