Faraday effect dispersion in nickel and permalloy thin films

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Abstract
Faraday rotations in nickel and permalloy films up to 80‐20 Ni‐Fe compositions have been obtained at both normal and oblique incidence. Incident light was parallel to the magnetic field which ranged up to 8 kilogauss. For oblique incidence a graphic analysis of Faraday rotation vs. applied field yields both the magnetization and specific rotation. The dispersion curves for both the nickel and the permalloys show rotations which increase in moving from higher to lower energies in the range 0.7 to 3.0 eV. Rotation peaks occur at 1.2 eV for the nickel and at 1.7 eV for 80‐20 permalloy. We identify the peak in nickel with that shown in earlier MOKE conductivity measurements. Identical structure with shift to higher energies is exhibited by the permalloys. We attribute the shift primarily to an equivalent lowering of the Fermi level as iron is added to the nickel.