Faraday rotation spectra of Co 2+ at distorted octahedral sites in magnetic oxides

Abstract

Faraday rotation (FR) spectra of Co 2+(3d) 7 ions with high spin state at distorted octahedral sites in magnetic oxides are calculated on the basis of the crystal field theory. Since the spin-allowed transition from the ground 4T 1[(t 2) 5{ 2T 2}e 2{ 2A 2}] to the excited 4T 2[(t 2) 4{ 3T 1}e 3{ 2E}] states only contributes to the FR in the visible wavelength region, the FR spectra for this transition are calculated by taking account of the spin–orbit interaction V(SO), the low symmetry field V(D 2d), and the molecular field V(MF). Using the transition strengths calculated by the Racah–Wigner calculus, the FR spectra are calculated as a function of Δ / ζ , where Δ and ζ are parameters for V(D 2d) and V(SO), respectively. As a result, the FR at low temperature was found to change from a dispersive shape to an absorptive one as Δ / ζ becomes positive to negative.