| The optical conductivity and the magneto-optic polar Kerr effect of RAl 2 (R = La, Ce, Pr), RFe2 (R = Y, Ce), RNi 2B2C (R = Tm, Yb), CeB6, and YbBiPt were measured between 1.4 and 5.4 eV using a rotating analyzer ellipsometer and a normal incidence Kerr spectrometer. Optical absorption of RAl2, RFe 2, and RNi2B2C shows metallic behavior. For the low carrier concentration metals CeB6 and YbBiPt the spectrum is dominated by interband transitions. Spectra of RAl2 and RFe 2 show absorption at 2 eV which is also found in heavier RFe2 compounds. This structure is attributed to R-derived transitions. At higher energy transitions are governed by Fe-derived states. Alloying CeFe2 with 10% Co leads to a magnetic instability with a low-temperature antiferromagnetic ground state. The metamagnetic transition to the field-induced ferromagnetic state was observed using the Kerr effect. We measured the Kerr rotation at 1.8 and 4 eV across this transition, which occurs between 35 and 40 kOe at 50 K. For the magnetic superconductor TmNi2B2C the transition from the superconducting to the normal state was found in the Kerr rotation. A critical field of 10 kOe was estimated, which is in excellent agreement with the value derived from magnetization data. CeB6 shows a peak in the Kerr effect, which coincides with the plasma edge at 2 eV. No such feature was found in YbBiPt. The plasma edge appears to be screened by interband transitions.;We used the tight-binding linear muffin-tin orbital method to calculate the band structure and density of states. The spin magnetic moment obtained by the local density approximation (LDA) is generally in good agreement with experiment. The orbital moment of localized states is overestimated by LDA. For the more itinerant 4f states found in CeFe2 the magnetic moments predicted by LDA are close to the experimentally observed moments. The optical conductivity for LaAl2 and YFe2 agrees well with the one measured. LDA does not reproduce the conductivity for the other compounds, which we attribute to an inadequate treatment of the localized 4f states in the LDA. Spectra were analyzed using band structure plots which included the orbital character of the bands. |
