Magneto-optical spectroscopy of d- and f-ferromagnetic materials: recent theoretical progress (Review Article)

The current status of theoretical understanding of the optical and magneto- optical (MO) spectra of 3d, 4f and 5f compounds is reviewed. Energy band th eory based upon the local spin-density approximation (LSDA) describes the o ptical and MO spectra of transition metal compounds reasonably well. Exampl es which we examine in detail are XPt3 compounds (with X=3d V, Cr, Mn, Fe, and Co) in the AuCu3 structure, ternary Heusler alloys NiMnSb, PdMnSb, PtMn Sb, and MnBi compound. The LSDA, which is capable of describing the spectra of transition-metal alloys with high accuracy, does not suffice for lantha nide compounds having a correlated 4f shell. A satisfactory description of the optical spectra could be obtained by using a generalization of the LSDA , in which explicitly f electron Coulomb correlations are taken into accoun t (LSDA+U approach). As examples of this group we consider CeSb and CeBi. F or CeSb a record Kerr angle of 90 degrees was very recently reported, 90 de grees is the absolute maximum value that can be measured. It is two orders of magnitude larger than the values that are commonly measured for transiti on-metal compounds, and about one order of magnitude larger than values max imally achieved for other lanthanide and actinide compounds. A third group consist of uranium 5f compounds. In those compounds where the 5f electrons are rather delocalized, the LSDA describes the MO spectra reasonably well. As examples of this group we consider UAsSe and URhAl. Particular difficult ies occur for the uranium compounds where the 5f electrons are neither delo calized nor localized, but more or less semilocalized. Typical examples are US, USe and UTe. The semilocalized 5f's are, however, not inert, but their interaction with conduction electrons plays an important role. Recently ac hieved improvements for describing such compounds are discussed. (C) 1999 A merican Institute of Physics. [S1063-777X(99)00106-1].