Exchange Splitting of ³T_2g Band in Antiferromagnetic KNiF₃

Abstract

Absorption spectra of the ³T_2g band in KNiF₃, KMgF₃: 1.5%Ni and K₂NiF₄ are measured at 2 K. In the antiferromagnetic KNiF₃, splitting of the Γ₃ line in the ³T_2g band is observed. Large linear dichroic spectra are obtained in the ³T_2g band of KNiF₃ under the ⟨001⟩ and ⟨111⟩ stress. This linear dichroism is induced by the movement of domain walls so as to align spins along the applied stress. The stress effect of the split Γ₃ lines is explained by the exchange interaction in the ³T_2g state. The exchange constant J′ is determined to be 7.5 cm⁻¹ for spins aligned along the ⟨001⟩ direction, and 8.7 cm⁻¹ for spins aligned along the ⟨111⟩ direction.