abstract
- In this work, the near-surface chemical and electronic properties of NiFe2O4 (NFO) thin films were systematically investigated using X-ray photoelectron spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS). NFO films were deposited on Si (111), MgO (100), and SrTiO3 (100) single-crystal substrates by RF magnetron sputtering. X-ray diffraction (XRD) revealed a highly textured NFO film oriented along the [001] direction on SrTiO3 (100) and a polycrystalline structure on Si (111), both corresponding to the Fd3m space group of the bulk target. High-resolution XPS spectra evidenced a non-stoichiometric surface composition, with Fe/Ni atomic ratios ranging from 1.35 to 2.53 and the coexistence of Fe2+and Fe3+species. REELS measurements indicated highly resistive behavior with band gap energies of 1.7 eV and 1.96 eV, while vibrating sample magnetometry (VSM) confirmed weak ferromagnetic behavior in all samples. The results demonstrate the successful growth of non-stoichiometric ferrites, with magnetic properties strongly influenced by the substrate type due to variations in cation distribution and octahedral distortions arising from lattice mismatch.