ANALYSIS OF MAGNETIC AFTER-EFFECT SPECTRA IN ZINC FERRITES

The magnetic after-effect (MAE) spectra occurring in vacancy-doped (De lta) zinc ferrites, Fe3-x-DeltaZnxO4 (0.1 less than or equal to x less than or equal to 0.5; 10(-5) < Delta < 10(-3)), have been investigate d in the temperature range 4 K < T < 460 K. The order-dependent relaxa tion processes below the Verwey temperature (T-V less than or equal to 125 K), i.e. tunnelling and long-range hopping of electrons, are seve rely affected over the whole range of Zn2+ substitutions. Thus, only t he vacancy-mediated high-temperature ionic relaxations of superimposed type mi and III2 (near 300 K), and of satellite-type II (T greater th an or similar to 380 It) could be quantitatively evaluated to yield th e following averaged activation parameters, for III1, III2: Q(1) appro ximate to 0.84 eV: Delta Q(1) approximate to 0.15 eV, tau(0,1) approxi mate to 2.3 x 10(-14) s; Q(2) approximate to 0.93 eV; Delta Q(2) appro ximate to 0.12 eV, tau(0,2) approximate to 0.9 x 10(-14) and for II: Q = 1.05 eV, Delta Q approximate to 0.21 eV: tau(0) approximate to 1.7 x 10(-14) s. All ionic relaxations are interpreted in terms of a modif ied vacancy model, as known from magnetite research.