ON THE NATURE OF THE ABSOLUTE MAXIMAL OBSERVABLE MAGNETOOPTICAL KERR ROTATION OF CESB

We report first-principles calculations of the polar magneto-optical ( MO) Kerr spectra of the Ce compounds CeSb, CeSb0.75Te0.25, CeTe, and C eSe, using the local-density approximation (LDA) of density-functional theory as well as its generalization which contains an explicit Coulo mb interaction U (LDA+U). Although the LDA predicts a large Kerr rotat ion of about 20 degrees in CeSb, we find that the LDA+U gives a better description of the Kerr spectra of all four compounds. For CeSb the L DA+U predicts a colossal Kerr rotation of 45 degrees up to 60 degrees, in agreement with the recent discovery of the maximal observable rota tion of 90 degrees in CeSb by Pittini et al. (Phys. Rev. Lett., 77 (19 96) 944). The origin of the colossal Kerr rotation realized in CeSb is examined.