Multispin Axis Structures for Antiferromagnets

Abstract

Neutron diffraction intensities have been computed for antiferromagnetic spin arrangements in the rock-salt-type structure. If the spin directions in the unit cell occur at relative angles other than 0\ifmmode^\circ\else\textdegree\fi{} or 180\ifmmode^\circ\else\textdegree\fi{}, the neutron scattering from powder specimens does not lead to a unique solution of the spin arrangement. A unique solution can be obtained from neutron scattering by a single-domain crystal. Neutron diffraction from crystals of nickel oxide shows that in all crystals examined, either the magnetic moments were parallel to more than one direction in the crystal, or antiferromagnetic domains were present. The results can be quantitatively accounted for by assuming the crystal consisted of domains with a common magnetic axis.