Optical and magneto-optical properties of (CoFe)x(HfO21)1−x magnetic granular films

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Abstract
Granular films of composition (CoFe)x(HfO2)1−x with continuous variation of the Co0.5Fe0.5 volume fraction in the range 0.1<x<1 have been prepared by e-beam co-evaporation. The optical properties of the granular films have been determined from transmission and reflection spectra in the 300–1100 nm region. The optical characteristics of the films as a function of x were also determined by the ellipsometrical method at λ=632.8 and 830 nm. The Faraday rotation in the films was determined at λ=632.8 nm. We find that the transmission and reflection spectra and the dielectric function have anomalies near the percolation threshold at x≈0.45. The spectral dispersion of Faraday effects has a peak in the region of the plasma frequency. The Faraday effect is greatly enhanced near xp. We also find that the extraordinary Hall resistivity, measured at room temperature and at 8 kOe of applied field, increases dramatically from 0.2 to about 600 μΩ cm near the percolation threshold. These films also possess large magnetoresistance, whose values are about 4% in maximum for x=0.35–0.45. The calculated optical and magneto-optical parameters and the extraordinary Hall resistivity, described in the framework of the effective medium approximation, are in qualitative agreement with experimental data.