Stress induced magnetic anisotropy in natural single crystals of hematite

The stress induced anisotropy has been determined for several natural crystals of hematite for compressions of up to 300 Kg/cm2 along the trigonal axis and along different directions within the basal plane. The induced anisotropy is predominantly uniaxial, but substantial higher harmonics are present for compressions along the trigonal axis. It is larger for compressions within the basal plane in accordance with the magnetostriction experiments of Urquhart and Goldman. Stress induced anisotropy as a possible explanation of the high coercive forces of hematite powders is discussed, as shape and intrinsic crystalline anisotropy are negligible.