Magnetic Ordering and LowNi2+Moment in CsNiCl3

Abstract

The magnetic structure of CsNi${\mathrm{Cl}}_3$ has been carefully reexamined by single-crystal neutron diffraction techniques in view of an apparent inconsistency between previous powder neutron diffraction results and a recent NMR investigation. Intensity data were collected from two different-sized crystals taken from the sample used in the NMR study, and corrected for absorption and extinction effects. These data confirm that there is an antiferromagnetic transition at 4.3°K to the triangular arrangement of moments deduced in the previous study. In the region between 4.3 and 2.7°K the sublattice magnetization has a critical exponent $\beta$ of 0.27±0.03. A particularly striking result is that the magnitude of the ${\mathrm{Ni}}^{2+}$ moment extrapolated to 0°K is only $(1.\mathrm{}{0}_5\pm 0.1){\mu }_B$, indicative of very substantial zero-point deviation effects.