Dielectric behavior of spin-deposited nanocrystalline nickel–zinc ferrite thin films processed by citrate-route

Nanocrystalline nickel–zinc ferrite thin films with the general formula Ni1−xZnxFe2O4, where x=0.0, 0.2, 0.4 and 0.6 were fabricated via a chemical route known as the citrate precursor route. These films were spin-deposited on indium–tin oxide coated glass, fused quartz and amorphous Si-wafer substrates, and annealed at various temperatures up to 650 °C. The films annealed below 400 °C were found to be X-ray amorphous, while the films annealed at and above 400 °C were polycrystalline exhibiting a single-phase spinel structure. The average grain size of the films evaluated by transmission electron microscopy, is found to be in the range 4–8.5 nm. The room temperature DC resistivity of the films is in the range 103–107 Ω m. Dielectric constant and dielectric loss were measured in the frequency range 100 Hz–1 MHz. Dielectric constant of the films is found to lie between 25 and 44, while the loss factor is if the order of 10−2. The higher values of the dielectric constant for films having higher zinc concentration are attributable to the enhanced hopping between Fe2+ and Fe3+ ions in these samples. The M–H hysteresis measurement of the nickel ferrite thin films annealed at 650 °C showed narrow hysteresis loop—a characteristic of soft ferromagnetic material.