Impedance spectroscopy of Zn0.3Ni0.7Fe2O4/ZnO-rGO composite heterostructure

In an attempt to study the effect of interface on light (660 nm) and magnetic field dependent electrical transport through Zn0.3Ni0.7Fe2O4/ZnO-rGO composite heterostructure we have performed detailed impedance spectroscopy and required fitting analysis. The fittings have been carried out by using equivalent parallel RC circuit which may correspond to the Zn0.3Ni0.7Fe2O4/ZnO-rGO composite interface that dominates in our impedance data. Under application of 2 kOe magnetic field (H), equivalent R is observed to decrease from 11.018 M omega to 9.790 M omega and from 14.524 M omega to 13.697 M omega, whereas equivalent C is observed to increase from 467.24 pF to 485.43 pF and from 549.83 pF 615.00 pF for fittings of Z' vs. f and Z "vs. f curves, respectively. Under dark, the variation of R with H may possibly be controlled by magnetostriction of Zn0.3Ni0.7Fe2O4 and magnetic field assisted tunnelling. On the other hand, the observed rise in C with the rise in H may be attributed to the magnetoelectric coupling between magnetostrictive Zn0.3Ni0.7Fe2O4 and piezoelectric ZnO. Only under strong illumination of 3.08 mW/cm2, we observed relaxation peak at around 32.5 Hz which corresponds to the relaxation time around 4.9 ms. This observed relaxation peak may be attributed to the light assisted relaxation at the Zn0.3Ni0.7Fe2O4/ZnO-rGO composite interface. In order to meet our final aim, i.e., magneto -optic coupling, we have performed fittings of H dependent impedance data under high illumination of 3.08 mW/cm2. Under such strong illumination the nature of the Zn0.3Ni0.7Fe2O4/ZnO-rGO composite interface seems to be altered which causes H dependent increase in equivalent R and C.