Stirring-mediated anomalous dielectric behaviour of electrodeposited and in situ oxidized FeAl2O4 thin films

Abstract

Spinel ferrites, due to high permeability and stability, possess remarkable features that make them a favourable candidate for spintronic applications. Electrodeposition method is used for the synthesis of iron aluminium oxide (FAO) thin films. A series of samples are prepared by keeping deposition time constant at 10 min, and in situ oxidation time varied as 5 min, 10 min, 15 min and 20 min by anodic electrodeposition. These electrodeposited FAO thin films are annealed at 500 Oe applied magnetic field at 300 °C in vacuum. At 5-min oxidation time, mixed structural phases, i.e. FeAl2O4 and Al2O3, are observed, whereas phase-pure FeAl2O4 is observed at 10-min oxidation time. A further increase in oxidation time to 15 min and 20 min results in reappearance of mixed phases. Phase-pure FeAl2O4 thin film at oxidation time of 10 min exhibits bond angle of ~ 158.59° with + ive tilt ~ 4.59°. A decrease in bond angle (i.e. ~ 139.20°) with − ive tilt ~ − 14.8° is observed with an increase in oxidation time to 20 min. SEM micrographs show the formation of octahedral and dodecahedral grains for 10-min oxidation time with grain size in the range of 2–3 μm. FTIR and Raman analysis confirms the formation of FeAl2O4 thin film at 10-min oxidation time with the appearance of bands at 610.94 cm−1 and 753 cm−1, respectively. Magnetic hysteresis curves show a ferromagnetic behaviour of iron aluminium oxide thin films. Thin film prepared using 10-min oxidation time shows a relatively higher value of saturation magnetization Ms (17.89 emu/cm3). Anomalous dielectric behaviour is observed for FeAl2O4 thin films due to the resonance phenomena at higher frequencies. Dielectric constant of ~ 37.96 at log f = 5.0 is observed for 10-min oxidation time. Temperature-dependent dielectric study is also carried out in the temperature range of 30–210 °C. Fitting of Cole–Cole plots through ZView software shows a strong dependence of dielectric constant on grain boundary resistance. This is to be emphasized that detailed study on the dielectric and impedance properties of electrodeposited iron aluminium oxide thin films is rare to be found. Having knowledge of room temperature and temperature-dependent dielectric properties of iron aluminium oxide thin films will help in extending the field of application to the microelectronic industry.