Conductivity and magnetoresistance of FeSi in the Anderson-localized regime

Abstract

The temperature dependence of the conductivity, σ( T), of FeSi at T ≈ 100–170 K follows the Arrhenius law with the value of the band gap E g ≈ 50 ± 5 meV. Between T ν ≈ 15–25 K and T ν ∗ ≈ 3–4 K it agrees with the Mott-type varriable-range hopping. No tendency of saturation in σ( T) is observed down to 1.4 K. The relative magnetoresistance, Δϱ/ϱ, is negative at T ⩽ 4.2 K and H < 1 T with the amplitude value ≈0.2%. In higher fields, up to 35 T, it is positive and demonstrates a complex magnetic field and temperature dependence suggesting both positive and negative contributions. At T ⩾ 77 K, Δϱ/ϱ is negligible. The positive component of Δϱ/ϱ agrees with that of the Osaka model which takes into account both correlation and spin-flip effects. The negative contribution is attributed to the Zeeman splitting of the mobility threshold predicted by Kamimura and Kurobe. The temperature dependence of the hopping frequency with the pre-exponent ν 0 ≈ 2.8 × 10 12s −1, the value of the internal field, H I ≈ 60 kOe, and the maximum value of the correlation energy, U m ≈ 17 K, are obtained.