The puzzle of the 90 degrees Kerr rotation in CeSb

We performed magneto-optical investigations of the polar Kerr rotation on n ew CeSb samples, focussing our attention on the reproducibility and intrins ic nature of the 90 degrees Kerr rotation found by Pittini et al. [R. Pitti ni, J. Schoenes, O. Vogt, P. Wachter, Phys. Rev. Lett., 77 (1996) 944]. Sur prisingly, we were not able to reproduce this remarkable result on new and well characterized CeSb samples. The maximum value of the Kerr rotation is -17 degrees at 0.46 eV. Possible origins of this puzzling result are discus sed. (C) 1999 Elsevier Science Ltd. All rights reserved.