Paramagnetic Resonance of Fe(II) Ions in Single Crystal CdCl2

The paramagnetic resonance of Fe(II) ions in single crystal CdCl2 has been studied in order to determine the strength of the trigonal crystal field, δ, relative to that of the spin‐orbit coupling parameter, λ′. The ratio δ/λ′ determines the nature of the magnetic properties of FeCl2. Kanamori originally proposed |δ/λ′|≫ 1 which leads to an effective Ising model of spin 12. We find for Fe(II) in CdCl2, however, that δ/λ′=−0.4, in qualitative agreement with the value −0.85 calculated from the magnetic susceptibility data on pure FeCl2. Thus we confirm that the magnetic properties of FeCl2 should be treated in terms of an effective spin S = 1.