Optical Measurements in Erbium Iron and Erbium Gallium Garnet

Optical absorption spectra of erbium iron garnet (ErIG) have been measured at 4.2°, 20°, and 62°K with external magnetic fields up to 25 kOe. From these measurements, the magnetic moment of the groundstate for the two magnetically inequivalent sites can be deduced as μ₁=7.0 μ_B and μ₂=4.6 μ_B yielding an average moment of μ=5.4 μ_B in the [100]‐direction. In addition, we have measured the G‐tensor of one excited state (⁴I_9/2) as G_x=(10.0±0.5) cm⁻¹, G_y=(15.0±0.5) cm⁻¹, and G_z=(10.0±0.5) cm⁻¹. The comparison with the g‐tensor of this state in the gallium garnet (g_x=3.1, g_y=3.1, g_z=3.9) shows a large anisotropic exchange. Crystal‐field energy levels and g‐factors of erbium gallium garnet and erbium aluminium garnet have been measured and a good fit to a set of nine crystal‐field parameters $A_k^q{\mathrm{〈r}}^k〉$ has been obtained.