Analysis of magnetic after-effects in nickel ferrites

Of the magnetic after-effect (MAE) spectra occurring in vacancy-doped (Δ) nickel ferrites, Fe3-x-ΔNixO4, of compositions 0.1 ≤ x ≤ 0.8 and Δ ≅ 5 x 10-3, in the temperature range 4 K < T < 460 K only the B-site vacancy-mediated ionic relaxations of type III, near 300 K, prove to be accessible to quantitative analysis. All other processes such as (i) electron tunnelling (4 K < T < 35 K), (ii) long-range electron hopping (50 K < T < 125 K), (iii) ionic relaxations of type II (T > 350 K) are so seriously affected by the Ni-induced Anderson localization of electrons as to allow only qualitative conclusions to be drawn. The activation parameters deduced for the composed process III - Q1 ≅ 0.87 eV, ΔQ1 ≅ 0.12 eV, τ0.1 ≅ 4.0 x 10-14 s and Q2 ≅ 0.95 eV, ΔQ2 ≅ 0.14 eV, τ0.2 ≅ 4.2 x 10-14 s - compare well with those determined in magnetite and related compounds, thus supporting the underlying relaxation model. (orig.)