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Recent neutron scattering work on the planar antiferromagnet K2NiF4 has indicated that this system undergoes a true two-dimensional antiferromagnetic phase transition. In this paper we review these studies together with measurements of the magnons at low temperatures and in the vicinity of TN. New high precision measurements of the sublattice magnetization around TN are presented. It is shown that the power law M(T)/M(4.2)=0.973(1−T/92.23)0.138±0.004holds for 2×10−1 1-T/TN 3×10−4. Preliminary measurements of the wavevector-dependent staggered susceptibility χαβ (q) in K2NiF4 show that only χzz, the component parallel to the anisotropy axis, has pronounced diffusive character, diverging at TN. This provides definitive proof that the phase transition is anisotropy-induced.
Birgeneau et al. (1970) studied this question.