The optical and magneto-optical properties and magnetoresistance of amorphous CoFeNiSiB alloys

The optical and magneto-optical properties of amorphous CoFeSiB ribbons wer e investigated for incident photons in the energy range from 0.05 to 2.2 eV . The diagonal and off-diagonal optical conductivities were determined from the results of spectroscopic ellipsometry and magneto-optical Kerr effect measurements. The Kerr rotation spectra for the amorphous films have a shap e in the 0.6-2.2 eV region that is quite similar to that of bulk Co. The op tical conductivity of the amorphous CoFe(Ni)SiB alloys increases slowly as a function of frequency (proportional to omega(1/3)) in the IR region. Such a sigma similar to omega(1/3) dependence in the IR region suggests an addi tional localisation of the electron states. A large room-temperature magnet oresistance effect has been demonstrated in thin Co71Fe7Si12B10 and Co59Fe5 Ni10Si11B15 amorphous ribbons for AC at applied fields, H < 80 Oe. The peak value of the magnetoresistance ratio is very sensitive to the Co and Fe co ncentration in the alloys. The dependence of the magnetoresistance for amor phous alloys is consistent with a theoretical model in which the resistivit y arises from the scattering of the conduction electrons by a domain wall i n the weakly localised regime. (C) 2000 Elsevier Science B.V. All rights re served.