Faraday rotation in erbium-yttrium iron garnet

Faraday rotation of Er2.2Y0.8Fe5O12(ErYIG) single crystals has been measured at 1150 nm wavelength in order to compare with that of pure Er3Fe5O12(ErIG). The measurements have been performed in the 77-300 K temperature range in magnetic field up to 20 kOe applied along the |111| |110| and |100| directions. It is shown, under the assumption that the Fe³⁺contribution is the same as in YIG, that the magnetooptical coefficient of Er³⁺ions is the same in ErYIG as in ErIG. This coefficient, related to the electric dipole transitions, is found to present a linear temperature dependence.