Faraday Rotation in Rare-Earth Iron Garnets

The Faraday rotation of yttrium, gadonlinium, and terbium iron garnets at 1.15 μ is presented as a function of temperature between 100 and 450°K. The rotation is analyzed in terms of electric and magnetic dipole contributions from the various magnetic sublattices (${\mathrm{Fe}}^{3+}$ octahedral, ${\mathrm{Fe}}^{3+}$ tetrahedral, R${\mathrm{E}}^{3+}$), and the contributions are separated by a least-squares fit to magnetization data. The similarities and differences in the electric dipole contributions are discussed, and it is suggested that charge-transfer processes are important. The effect of a knowledge of the electric dipole contributions at 1.15 μ on published results at longer wavelengths is investigated, and deductions of $g$ factors in this region are shown to be probably in error. In an Appendix, theoretical derivations are given for the form of the electric dipole rotation due to magnetic ions in various circumstances.