Four-Level Transition Analysis of the Polar Kerr Effects in Ferrornagnetics

In ferromagnetics, besides originating from the splitting of the excited state resulting from the spin-orbit interaction, magneto-op tical effects also stem from the splitting of the ground state caused by the exchange interaction and the applied field. Theoretical calculation according to this view shows that, in ferromagnetics, there are electron transitions corresponding to two pairs of left- and right-handed circularly polarized lights, and the polar Kerr rotation θ_κ depends linearly on magnetization M in both regions of low temperature and high temperature for the material with high Curie temperature T_c. When considering the different oscillator strengths in normal temperature region between the above two regions, we obtain the expressions of θ_κ as forms similar to θ_κ ≅∑_n=0α(M/T)ⁿ and θ_κ≅∑_n=0βM^n+l/Tⁿ.