Magneto-optical properties of Al-substituted erbium iron garnet single crystals

The magneto-optical (MO) properties of Er3Fe5−zAlzO12 (z=0.35 and 0.55) single crystals, where Al3+ ions show a large preferentially tetrahedral Fe3+ replacement, are presented and compared to those of pure ErIG and octahedrally substituted ErIG:Sc compounds. Faraday rotation (FR) Φ measurements at 1152 nm wavelength were performed in the 6–600 K temperature range under a magnetic field up to 20 kOe applied parallel to the [100] and [111] crystallographic axes of the “as-grown” crystals. For both Al concentrations, within experimental accuracy, the measured anisotropy of the spontaneous FR is weak (less than 10%) or absent. Sample with z=0.35 is nearly isotropic. In contrast to ErIG:Sc, the FR susceptibility χF(T)=dΦ/dH deduced from the saturated part of the different FR curves shows no anisotropy. The analysis of the MO properties of the compounds is performed using the one ion model and assuming the total Fe3+ MO contribution is represented by the magnetooptical measurements performed on YIG:Al single crystals of same composition. The temperature variation of the Er3+ FR contribution ΦEr shows that the FR due to magnetic dipole transitions compensates the electric dipole contribution when T/TNéel∼0.13, and is not affected by diamagnetic tetrahedral (Al3+) or octahedral (Sc3+) Fe3+ substitutions. The magneto-optical electric dipole coefficient Ce of the Er sublattice is also shown to be a function of temperature.