Structural and optical properties of nickel aluminate spinel ferrite thin films prepared by spray pyrolysis technique

In this paper, we report the preparation of nano-crystalline thin films of nickel aluminate spinel ferrite having the chemical formula NiFe_2−xAl_xO₄, where Al³⁺ varies from 0.0 to 0.4 with rise in 0.1, using the well-known spray pyrolysis deposition method. The thin films were grown and deposited on ultrasonically clean glass substrate. The X-ray diffraction pattern show orientation of various is diffraction peaks at (220), (311) (222), (400), (422), (511), and (440). The presence of this diffraction peak suggests the formation of single-phase compound as there are no extra diffraction peaks in the XRD pattern other than cubic spinel phase. The crystallite size deduced from the Debye–Scherrer equation varies in the range 19–14 nm. The Lattice parameter found to decrease with doping of Al³⁺ ions. FTIR spectra show the absorbance bands are close to the 400 cm⁻¹ and 600 cm⁻¹ wave number which are attributed to stretching vibrations of metal–oxygen bond. The presence of five active modes in Raman spectra confirm the ferrimagnetic spinel structure of the thin film. Field emission scanning electron microscopy (FESEM) shows the spherical grain morphology with some agglomeration. Energy-dispersive X-ray analysis (EDAX) spectra show the presence NiFe_2−xAl_xO₄ elements in stoichiometric proportion. The ohmic nature of the prepared thin film was confirmed through I–V characteristics. The band gap energy estimated through UV–visible technique varies in the range of 2.05–1.14 eV indicating the semiconducting behavior of the prepared thin films. The obtained results are useful for opto-electronic devices.