Electric-field-driven resistive transition in multiferroic SrCo2Fe16O27/Sr3Co2Fe24O41 composite

We report on the observation of electric-field-driven resistive transition [abrupt rise in resistivity (ρ)] at a characteristic threshold field Eth(T) in an off-stoichiometric composite of W- and Z-type hexaferrite (∼80%)SrCo2Fe16O27/(∼20%)Sr3Co2Fe24O41. The dielectric constant ε and the relaxation time constant τ also exhibit anomalous jump at Eth(T). The Eth(T), the extent of jump in resistivity (Δρ), and the hysteresis associated with the jump [ΔEth(T)] are found to decrease systematically with the increase in temperature (T) across a range of 10–200 K. They also depend on the extent of nonstoichiometry. In addition, several temperature-driven phase transitions have been noticed both in the low and high resistive states. The entire set of observations has been discussed within the framework of structural evolution of the point defect (cation vacancies or oxygen excess) network and its influence on electronic conduction. The magnetocapacitive effect, measured under ∼20 kOe field, turns out to be substantial (∼4%–12%) and exhibits clear anomaly at Eth. This comprehensive map of esoteric ρ−E−T and ε−E−T patterns provides insights on defect-driven effects in a multiferroic composite. These effects could be useful for tuning both the resistive transition and the multiferroicity.