Abstract
Measurement of the magnetic anisotropy energy of a single crystal of natural pyrrhotite in c-plane was made by means of the torque method at room temperature up to a magnetic field of 20000 oe and at low temperature in a constant field. It was found that the easy axis lay along [2\bar10] direction above −80°C which, however, changed to [100] direction below that temperature. The torque curves in c-plane were composed of two- and six-fold symmetric parts. It was also found that in the range of strong magnetic fields the six-fold symmetric part at room temperature decreased with the inverse square of the applied field; such a field dependence is explained assuming a triad structure for the single crystal of pyrrhotite. A remark is also given on the origin of the two-fold symmetric torque.
