Magnetocrystalline Anisotropy of Pyrrhotite

Magentization curves in the base plane and along the c-axis of natural pyrrhotite crystals (Fe_7S_8) are measured up to a magnetic field strength of 90 kOe. The results can be expressed in terms of the magnetocrystalline anisotropy energy, E_K=-K_0|cos θ|+K_3 cos^2θ+K_4cos^4θ, the last term being the correction term for the. preceding one. The values of K_0, K_3 and K_4 obtained are K_0=0.51×10^6erg/cc, K_3=3.2×10^6 erg/cc and K_4=0.098×10^6 erg/cc at 293°K and K_0=1.2×10^6 erg/cc, K_3=4.2×10^6 erg/cc and K_4=0.21×10^6 erg/cc at 77°K. These values obtained are discussed on the basis of Adachi\u27s theory of magnetocrystalline anisotropy