Magnetic Dipole Optical Absorption Spectrum of MnF2

Abstract

We present quantitative intensity measurements on six magnetic dipole absorption transitions in MnF₂ as well as some high‐magnetic‐field experiments with components of the field along both the $c$ axis and in the basal plane. We interpret these results and those of previous investigators on the ${}^4{T}_1\mathrm{(I)}$ , ${}^4{A}_1{}^4\mathrm{E(I)}$ , ${}^4{T}_2\mathrm{(II)}$ , and ${}^4{T}_1\mathrm{(II)}$ states, at first using a crystal‐field calculation which ignores the vibronic aspects of the problem. With this calculation we can phenomenologically obtain the low‐symmetry‐field energy‐level scheme and explain the effects of high magnetic fields on the spectrum, but we cannot obtain a consistent set of one‐electron low‐symmetry‐field parameters for all the excited states. By considering the vibronic problem, we find that we can understand all the excited states in a consistent manner, and explain the small spin–orbit coupling in the ${}^4{T}_1\mathrm{(I)}$ state. In addition, we show that for the nearly degenerate ${}^4{A}_1{}^4\mathrm{E(I)}$ states, the ${}^4{A}_1$ state does not lie low.