Absorption and Reflectivity Measurements on Some Rare Earth Iron Garnets and α-Fe2O3

Measurements of the absorption coefficient of (111) crystal sections of $\mathrm{\alpha -}{\mathrm{Fe}}_2{\mathrm{O}}_3$ were made in the visible and near infrared. Absorption peaks were observed centered at energies of about $\text{12000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ and $16000{\mathrm{cm}}^1$ . Reflectivity measurements on the $\mathrm{\alpha -}{\mathrm{Fe}}_2{\mathrm{O}}_3$ crystals were carried out in the $\text{30000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ to $\text{400\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ range. Broad reflectivity peaks are found in the near ultraviolet at $\text{24500\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ and $\text{26000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ , respectively. Very strong reflection peaks resulting from the lattice vibrations are present at energies smaller than $\text{700\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ . Several quite sharp peaks are found in the absorption spectra of the rare-earth iron garnets of Dy, Ho, Er and Yb in the $\text{10000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}\text{–13000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ energy range. The circular dichroism of ytterbium iron garnet is displayed by means of absorption curves for the two senses of circularly polarized light.