MAGNETIC AFTER-EFFECTS IN NICKEL FERRITES AND THEIR INTERRELATION WITH ELECTRICAL-CONDUCTIVITY

The magnetic after-effect (MAE) spectra of vacancy-doped (Delta) nicke l ferrites, Fe3-x-DeltaNixO4, of compositions 0.1 less than or equal t o x less than or equal to 0.8 and Delta similar or equal to 5 x 10(-3) are studied in the temperature range 4.4 K < T < 460 K. Ni2+ ions, lo cated preferentially on B-sites of the inverse spinel lattice, influen ce severely the magnetite-specific electron transport mechanisms: (i) electron tunnelling (4 K < T < 35 K) is suppressed for all Ni contents , x; (ii) wide-range electron hopping (50 K < T < 125 K) only occurs, in mutilated form, for 0.1 less than or equal to x < 0.4; (iii) the ch aracteristic Verwey transition (T-V similar or equal to 125 K), too, i s suppressed for all x; (iv) the vacancy-mediated ionic relaxations, n ear 300 K, are deteriorated for x < 0.4 but regain Debye-type characte r for x greater than or equal to 0.4. The interrelations between the M AE and the electric conductivity in Ni ferrites are discussed.