Optical and magneto-optic Kerr effects of MnBi, Ni2MnGa, and Gd5Si2Ge2

The magneto-optic Kerr angle spectrum of a single crystal of MnBi was measured at room temperature and also calculated with the TB-LMTO methods including the spin-orbit interaction. Previously measured Kerr spectra with thin films had two negative peaks, except for one film grown in ultra high vacuum. The later had a first peak and a shoulder at the second peak position, indicating the second originated from oxygen in the other films. Comparing first-principles calculations and previous thin-film results with our single crystal data indicated that the second peak originated from the combination of a weak intrinsic MnBi peak and oxygen in the sample. The complex dielectric constants and magneto-optic Kerr spectra of electro-polished (100), (110), and (111) planes Ni2MnGa were measured. Also optical and magneto-optical spectra were calculated with the TB-LMTO methods including the spin-orbit interaction. Measured Kerr and optical spectra with three surfaces at room temperature had the same peak positions, but different amplitudes. The difference between (100) and (110) surfaces are probably due to the polishing process, not intrinsic bulk properties. Angle-dependent reflectance difference spectroscopy of (100), (010), and (001) planes Gd5Si2Ge2, and (100) plane Tb5Si2.2Ge1.8, which are optically anisotropic materials, were measured with the Kerr spectrometer by rotating the samples. The replacing the rare earth Gd to Tb atoms and 10% changing Ge to Si atoms did not change the spectra much. The complex dielectric constants of (100) and (001) planes Gd5Si2Ge2 were measured by the spectroscopic ellipsometer. Two reflectance differences, measured by the Kerr spectrometer at near normal incidence and converted from the dielectric constants measured by ellipsometer at oblique incidence, agreed well