Shape Distribution of Magnetite Powders

The shape distribution curves of single‐domain magnetite powders calculated from magnetic data do not agree with those observed in the electron microscope. The Stoner‐Wohlfarth theory, from which the magnetic unaveraging process was derived, ignores magnetocrystalline anisotropy. This may be one of the contributory causes to the lack of agreement. To establish this, the shape curves were measured magnetically on both acicular and equant magnetite powders at various temperatures. The magnetocrystalline anisotropy of magnetite is temperature dependent, changing from about ${\text{−1\hspace{0.17em}×\hspace{0.17em}10}}^5\hspace{0.17em}\mathrm{ergs}/\mathrm{cc}$ at room temperature to ${\text{+1\hspace{0.17em}×\hspace{0.17em}10}}^5\hspace{0.17em}\mathrm{ergs}/\mathrm{cc}$ at −165°C. The magnetically calculated shape curves show some change with temperature; this indicates a contribution from the magnetocrystalline anisotropy.