Magnetic Anisotropy Measurements of NiO Single Crystal

The magnetic anisotropy of NiO single crystal grown by the Verneuil method was measured using a torque balance. An X-ray study showed that the crystal, despite its outward appearance of a single crystal, is composed of small rhombohedral domains twinned through {100} planes. By applying a pressure along one of the [111] axes of the crystal during annealing from above the Néel temperature, the twin structure was partly removed. Torque measurements in a homogeneous magnetic field and their analysis showed that in pressure-annealed crystals domains with trigonal axis pointing along the direction of the pressure dominate but antiferromagnetic domains in each crystallite are distributed at random. The spin axis was found to be in the plane parpendicular to the trigonal axis within ±16°.