Magnetic and electrical anisotropies of iron sulfide single crystals

Single crystals of iron sulfide of stoichiometric and near-stoichiometric compositions have been prepared by a method similar to the Bridgman technique, and their anisotropies of magnetic susceptibility and electrical conductivity have been observed. Consideration of the experimental results leads to the conclusion that the preferred direction of the antiferromagnetic spins is parallel to the c-axis of the crystal below Tα (the temperature of the α-transformation) and perpendicular to the c-axis above Tα. The behavior of the spin orientation in the temperature range between Tα and Tn (the Néel temperature) has been clarified. It appears that the anisotropy of conductivity can be explained qualitatively in terms of the dependence of electron scattering on the spin orientation of each magnetic ion in the crystal. Anomalous behavior of the susceptibility, which appears just below Tα in the cooling process, is reported briefly.