Origin of strong intrinsic Kerr effect in FePt and FePd ordered compounds

The magneto-optical spectra of chemically ordered FePt [001] and FePd [001] compounds are studied. The imaginary part of the off diagonal element, /spl sigma//sub 2xy/, of the conductivity tensor has two peaks located in the energy ranges 1.2-2 eV (Fe-like transitions) and 4-4.5 eV (Pt or Pd like transitions). The strength of these peaks is larger in FePt than in FePd and roughly scales with the spin orbit coupling of Pt and Pd d-bands in the ultraviolet spectral range. Large differences in the Fe dominated low energy side of the spectra suggest a much higher degree of electronic hybridization in FePt than in FePd.