Magneto-optical properties of KTb3F10 and LiTbF4 crystals

Single crystals of KTb3F10, LiTbF4, LiTb0.5Y0.5F4 and LiTb0.25Gd0.75F4 were prepared and the wavelength, temperature, and magnetic field dependence of the Faraday rotation measured. Optical-absorption spectra and refractive indices are also reported. The Faraday effect in these materials is described by a paramagnetic rotation with the primary oscillator strength arising from 4f8→4f75d electronic transitions of the Tb3+ ions. Whereas LiTbF4 orders ferromagnetically at low temperatures, the mixed crystals exhibited no ordering at T?1.25 K. Low-temperature Faraday rotation measurements of KTb3F10 do not indicate ferromagnetic order above 1.66 K. KTb3F10 and LiTbF4 crystals have large Verdet constants, are transparent in the visible and near infrared and have small nonlinear refractive-index coefficients. These materials are therefore useful for optical rotators and in high-power laser applications.