Faraday rotation of Hoya FR5 glass at cryogenic temperature

Faraday rotation and magnetization in Hoya FR5 glass is investigated in a magnetic field up to 80 kG under cryogenic temperature between 4.2 K and 10 K at the wavelength of 514.5 nm. For H/T≳10 kG K−1, the saturation is observed both in magnetization and in Faraday rotation and is interpreted by using the quantum theory of paramagnetism about the doped Tb3+ active ion. It is found that the temperature dependence of the Verdet constant is correlated with the magnetic susceptibility and the dispersion of the Verdet constant is due to the effective electric dipole transition of 4f8→4f75d1 with the resonance wavelength of 213 nm.