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 71 Fe 7 Si 12 B 10 and Co 59 Fe 5 Ni 10 Si 11 B 15 amorphous ribbons for AC at applied fields, H