Copper doped nickel ferrite nano-crystalline thin films: A potential gas sensor towards reducing gases

• Cu:NiFe2O4 thin films are synthesized by low cost spray pyrolysis technique.
• Addition of Cu content improves magnetic properties.
• Cu content on the surface of the film enhances the gas response.
• NiFe2O4 thin films exhibit predominant selectivity towards ethanol.
• 1 wt% Cu:NiFe2O4 film responses towards ethanol at lower optimum temperature.

NiFe2O4 and (1 wt% and 3 wt%) Cu:NiFe2O4 thin films have been fabricated using spray pyrolysis deposition technique at 350 °C and then sintered at 650 °C for 3 h. X-ray diffraction, SEM, EDAX, UV-VIS spectroscopy, SQUID VSM were carried out to investigate phase formation, microstructural and influence of Cu doping on magnetic properties of NiFe2O4 thin films. The gas response towards various gases viz. ethanol, Liquid Petroleum Gas (LPG), methanol and hydrogen sulfide (H2S) is investigated. The results of XRD revealed that all samples had shown the principal phase of nickel ferrite and the lattice parameter was found to vary from 8.294 Å to 8.314 Å on an incorporation of Cu, and the crystalline sizes were about 40–45 nm. The effect of Cu concentration on saturation magnetization and coercive force were studied. The maximum value of saturation magnetization calculated from hysteresis loop was 89.16 emu/g at room temperature and 96.88 emu/g at 50 K. Cu content on the film surface was found to be maximum for 1 wt% Cu:NiFe2O4 thin film and this film showed an improved response towards all gases. Response of ethanol for NiFe2O4 thin film was found to be higher as compared to all the other gases. The lowering of the optimum operating temperature is observed in 1 wt% Cu:NiFe2O4 thin film with higher selectivity towards ethanol than other gases. All results indicated that the Cu doping in nickel ferrite thin films has a significant influence on the properties.