The Faraday Effect in Garnets in the Infrared Region

The temperature dependence of the Faraday effect in $\mathrm{TbIG}$ was investigated in the infrared where the rotation $\mathrm{\alpha \phi }$ does not depend on frequency. It was shown that besides the change in the sign of $\mathrm{\alpha \phi }$ at the compensation point, there is another change in the sign of $\mathrm{\alpha \phi }$ at $\text{T\hspace{0.17em}=\hspace{0.17em}110°}\mathrm{K}$ . The temperature dependence of $\mathrm{\alpha \phi }$ agrees qualitatively with its theoretical behavior obtained in the infrared region from the off‐diagonal components of permeability tensor $\mathrm{[\mu ]}$ . For the quantitative agreement of the theoretical and experimental values of $\mathrm{\alpha \phi }$ , it is necessary to assume that the g‐factor of Tb³⁺ diminishes at low temperatures. The temperature dependence of the g‐factor of the Tb³⁺ ion in $\mathrm{TbIG}$ was determined, It was shown that in ${\mathrm{Bi}}_{\text{0.24}}{\mathrm{Ca}}_{\text{2.76}}{\mathrm{Fe}}_{\text{3.62}}{\mathrm{V}}_{\text{1.38}}{\mathrm{O}}_{12}$ at $\text{λ\hspace{0.17em}>\hspace{0.17em}4\hspace{0.17em}μ}$ the Faraday effect is positive and independent of $\lambda$ . The Faraday effect in the garnet has different signs in the infrared and visible regions. This fact is in accordance with the exchange mechanism of the Faraday effect observed in garnets in the infrared.