抄録
NiO crystals free from twin structure were prepared by annealing at 1650°C in argon atmosphere and either by axially cooling through the Néel temperature with a temperature gradient set along [111] or by applying a stress along [111] at room temperature. Torque measurements were made at various temperatures and in magnetic field up to 17 kOe. The results show that in the axially cooled crystal irreversible motion of S-walls, separating antiferromagnetic domains of different spin axes, takes place above 2 kOe for the field component in the (111) plane, and above 2.4 kOe the whole crystal forms nearly a single antiferromagnetic domain. In the stressed crystals these field values are higher. In both these crystals the torque in the [111]-rotation has a dominant sixfold component at high fields, which has the same magnitude for both crystals but is interpreted as being due to crystal imperfections. MnO was also studied and similar results were obtained.