Structural, optical and magnetic properties of vacuum annealed Fe, Mn doped NiO nanoparticles

Iron (Fe) substituted nickel oxide (Ni1−xFexO) and manganese (Mn) substituted (Ni1−xMnxO) nanoparticles at x = 0.05 were prepared using solid-state reaction. The synthesized Ni1−xFexO and Ni1−xMnxO nanoparticles were annealed in vacuum at a pressure of 1 × 0–3 mbar at two different temperatures of 473 K and 673 K for 1 h. The influence of vacuum annealing on the physical properties of Ni1−xFexO and Ni1−xMnxO nanoparticles were studied. The vacuum annealed nanoparticles were characterized by XRD, SEM, EDS, UV–Vis-NIR and VSM instruments to study their structural, surface, chemical, optical and magnetic properties, respectively. From the XRD results it was found that Ni1−xFexO nanoparticles were in cubic structure with Fe impurity phases whereas the Ni1−xMnxO nanoparticles exhibited cubic structure without any impurity phases. The crystallite sizes of the nanoparticles were in the range of 25–30 nm. From the EDS spectra, it was found that the elements such as Fe, Ni, Mn and O were in almost stoichiometric ratio. An increase in optical band gap for Ni1−xFexO and Ni1−xMnxO nanoparticles were observed with an increase of annealing temperature. The pure NiO and doped NiO nanoparticles exhibited ferromagnetism at room temperature. The strength of magnetization decreased in NiO with a rise in annealing temperature. The Ni1−xFexO and Ni1−xMnxO nanoparticles were ferromagnetic at room temperature and the magnetization increased with increase in vacuum annealing temperature. The highest magnetization of 1.4 emu/g, 0.85 emu/g and 0.76 emu/g were observed for NiO, Ni1−xFexO and Ni1−xMnxO nanoparticles, respectively at 673 K. The nanoparticles will be suitable for storage device applications.