Dynamical response of localized electron hopping and dipole relaxation in Cu1 − x Zn x Fe2O4 magnetoceramics

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We report a detailed study on the dynamical response of localized electron hopping and dipole relaxation in bulk polycrystals of Zn diluted Cuprospinel (Cu1 − x Zn x Fe2O4). The variations in the dielectric dispersion and ac-resistivity (ρ ac ) were analyzed over a wide temperature (77 K ≤T ≤ 823 K) and frequency (20 Hz ≤ f ≤ 20 MHz) window for a critical composition x c = 0.4. The variation of R (f, T) followed the Maxwell–Wagner type polarization mechanism in-line with the Koops phenomenological theory. Our analysis of ρ ac (T, f) provide strong evidence to the Mott’s variable range hopping of charge transport between the localized states at low temperatures, however, thermally-activated Arrhenius like behaviour was noticed at high temperatures with E A = 656 meV for x c = 0.4. Moreover, electric modulus spectroscopic studies (M *(f, T)) reveals two distinct types of relaxation phenomena: (i) the short-range oscillations of the charge carriers within the potential well of grains and (ii) the long-range movement of charge carriers across the grain boundaries. The depressed semi-circles of the Nyquist plots and lower values of non-exponential parameter extracted from M *(f, T) suggest the non-Debye type relaxation process present in the system with a widespread distribution of relaxation times. The frequency exponent (s(x, T)) study of Jonscher’s power law reveals that the ac-conductivity follows small-polaron tunnelling followed by the correlated-barrier-hopping mechanism for 0.1. However, for x ≥ x c reorientational hopping mechanism is predominant, except for 400 K, where thermally activated Arrhenius-type conduction of charge carriers is prevalent in this spinel system. Furthermore, the tetragonally (I41/amd) distorted systems (x ≤ 0.05) exhibit less activation energy (E A − VRH ) values as compared to those of cubic-spinel symmetry (Fd-3m) which saturates at 130 meV for 0.1 ≤ x ≤ 0.6. Compositional dependent tunability of the above discussed parameters may open a constructive approach to design low energy-loss and high-resistive electromagnetic elements for microwave devices which is the key significance of the present study.