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

Abstract

The optical and magneto-optical properties of amorphous CoFeSiB ribbons were 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 shape in the 0.6–2.2 eV region that is quite similar to that of bulk Co. The optical conductivity of the amorphous CoFe(Ni)SiB alloys increases slowly as a function of frequency (proportional to ω 1/3) in the IR region. Such a σ∼ ω 1/3 dependence in the IR region suggests an additional localisation of the electron states. A large room-temperature magnetoresistance effect has been demonstrated in thin Co 71Fe 7Si 12B 10 and Co 59Fe 5Ni 10Si 11B 15 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 concentration in the alloys. The dependence of the magnetoresistance for amorphous alloys is consistent with a theoretical model in which the resistivity arises from the scattering of the conduction electrons by a domain wall in the weakly localised regime.