ANALYSIS OF MAGNETIC AFTER-EFFECTS IN NICKEL FERRITES

Of the magnetic after-effect (MAE) spectra occurring in vacancy-doped (Delta) nickel ferrites, Fe3-x-DeltaNixO4, of compositions 0.1 less th an or equal to x less than or equal to 0.8 and Delta similar or equal to 5 x 10(-3), in the temperature range 4 K < T < 460 K only the B-sit e 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 hopp ing (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 ac tivation parameters deduced for the composed process III - Q(1) simila r or equal to 0.87 eV, Delta Q(1) similar or equal to 0.12 eV, tau(0,1 ) similar or equal to 4.0 x 10(-14) s and Q(2) similar or equal to 0.9 5 eV, Delta Q(2) similar or equal to 0.14 eV, tau(0,2) similar or equa l to 4.2 x 10(-14) s - compare well with those determined in magnetite and related compounds, thus supporting the underlying relaxation mode l.