A neutron diffraction study of weak ferromagnetism in nickel fluoride

Abstract

Polarised neutron diffraction data have been collected from single crystal samples of NiF₂ at 4.2K and in an external field of 1.4T. Subsidiary unpolarised neutron experiments carried out at a number of wavelengths have determined the extinction parameter and these have been used to correct the observed, polarised-beam flipping ratios. The geometry of the polarised neutron experiment was such that one group of reflections gives information solely on the distribution of the weak ferromagnetism, which corresponds to some 0.03 mu B/Ni²⁺ ion. The other reflections contain magnetic scattering from the antiferromagnetic component of the moment. Measurement of the flipping ratio of the (111) reflection has enabled the authors to verify the absolute configuration of the canted magnetic moments with respect to their octahedron of fluorine neighbors.