Magnetic Susceptibility of NiO and CoO Single Crystals

Abstract

The magnetic susceptibility of a NiO single crystal grown by the flame fusion method was found to be isotropic below the Curie temperature as it is for the case of powdered material. Such characteristics can be explained by twinning or domain structure within the crystal. Stressing the crystal along a [111] direction, while annealing, produces an anisotropic susceptibility with the maximum and minimum values found when the applied field was parallel and perpendicular, respectively, to the direction of stress. By using the Van Vleck theory, the results can be explained on the basis that the stress rotates some of the atomic spins from the direction of the [111] stress axis to the perpendicular planes. An assignment of spin direction to (111) planes of each domain agrees with the most recent neutron diffraction interpretation.