Abstract
An improved method is proposed of determining magnetic anisotropy constants for Alnico monocrystals subjected to the optimal field treatment. The magnetic torque curves are measured for the (001) disk specimen in various intensities of magnetic field, and then they are resolved by a harmonic analysis to obtain the Fourier coefficients. By postulating a uniform precipitate structure in the specimen, the formulae can be derived by which the uniaxial shape anisotropy constant as well as the cubic crystalline anisotropy constant can be separately evaluated with due consideration for a field dependence of the coefficients. For an Alnico 5 monocrystal treated in the optimal condition, the shape anisotropy constant and the magnetocrystalline one are (15.2±0.4)×105 and (1.6±0.2)×105 erg/cm3, respectively. Furthermore, similar measurements are made on Alnico 5 specimens field-treated in some directions deviating from the cube axis. These results can reveal the limitations on applications of the present method.
