Magnetic Anisotropy Constant of Yttrium Iron Garnet at 0°K

The anisotropy energy of yttrium iron garnet is separated into two parts, the normal part predominant at high temperatures, and the anomalous part important below 50°K. By comparison with ferrite data, the cause of the normal anisotropy is expected to be the coupling of the ${\mathrm{Fe}}^{3+}$ ions to the crystalline field. The following expression for $K_1$, the first-order anisotropy constant, as a function of the fine structure coupling constants $a_{24}$ (tetrahedral sites) and $a_{16}$ (octahedral sites) is obtained: $\frac{K_1}{\mathrm{unit}\mathrm{cell}}=-46.6\mathrm{}{a}_{24}-13.6\mathrm{}{a}_{16}$.