Dielectric Permittivity Tensor of ErFeO3 for Radiation in the Visible Spectrum

Abstract

As part of an effort to understand the nature of the transition responsible for the very strong absorption band edge and the large magneto‐optical effects in ferric ion containing ferro‐ and ferrimagnets, the optical and magneto‐optical properties of erbium orthoferrites (ErFeO₃, Θ_N = 620°K for Fe⁺³ spins) have been examined by reflection techniques. Ellipsometer and Kerr rotation measurements were made on growth surfaces (c plane) at room temperature over the visible spectrum. The real and imaginary parts of the dielectric constant show two bands at 22 000 and 26 000 cm⁻¹, with oscillator strengths of 0.03 and 0.4, respectively. The normal incidence polar Kerr rotation has a sharp peak of 11.5 min at 23 500 cm⁻¹. There are several weaker structures between 15 000 and 22 000 cm⁻¹ which are believed to be due to low‐lying branches of the crystal‐field spectrum of the Fe⁺³ ion. By combining the Kerr rotation and dielectric constant data, the off‐diagonal element of the dielectric permittivity tensor was calculated. The results suggest that the main 26 000 cm⁻¹ band and the unresolved 23 500 cm⁻¹ band represent the σ and π processes of the electron transfer transition. They further suggest that the π process component of the off‐diagonal element has opposite sign relative to that for the σ process and the first allowed internal transition.