Dielectric Constant and Magneto-Optical Kerr Rotation of Ferromagnetic Chromium Tribromide above the Absorption Band Edge

Abstract

By extending the optical and magneto‐optical measurements of the insulating ferromagnet CrBr₃ (hexagonal layer structure, T_c=36°K, and 4πM_s=3520 G) beyond the absorption band edge near 22 000 cm⁻¹ with reflection techniques, three absorption bands representing the π and σ processes of electron transfer transitions and an internal transition of Cr³⁺ have been observed. The room‐temperature dielectric constant was measured by means of an ellipsometer. The σ process and the internal transitions give rise to the two absorption bands at 24 310 cm⁻¹ and 29 580 cm⁻¹ with oscillator strengths of 0.30 and 1.61, respectively. They account for most of the dielectric constant. While the π process is too weak to be resolved in the dielectric constant data, it accounts for the main peak of the normal incidence polar Kerr rotation at 1.5°K of 3.5° at 23 500 cm⁻¹. The σ process accounts for the relatively sharp negative peak in the Kerr rotation of −2.5° at 26 700 cm⁻¹. The data further suggest that the π process component of the off‐diagonal element of the electric polarizability tensor has opposite sign to the σ process and the internal transitions.