Tuning the structural, optical and magnetic properties of PVP-capped NiO nanoparticles by gadolinium doping

Pure and Gd-doped NiO nanoparticles capped by polyvinylpyrrolidone (PVP) were synthesized via the co-precipitation method, with different concentrations (x = 0.000, 0.005 and 0.010). Extensive experimental assessments were conducted to study the structural, optical and magnetic properties of the prepared nanoparticles. The X-ray diffraction patterns depicted the formation of pure NiO phase without impurities, assuring the adequate incorporation of Gd dopants into the lattice. The transmission electron micrographs showed the pseudospherical morphology of the pure and Gd-doped samples, with mean sizes, ranging between 28.09 and 22.84 nm. The vibrational spectroscopies confirmed the purity of the synthesized samples and gave insight into their structural properties. Moreover, the excitation dependence of the photoluminescence emission spectra was noticed due to the particles' size distribution. Some point defects, as the nickel and oxygen vacancies, were tuned upon the introduction of Gd dopants, leading to enhancements in the optical and magnetic properties. The optimum concentration of Gd dopants was x = 0.005 in Ni1-xGdxO nanoparticles since it attained the widened bandgap energy of 3.46 eV and highest saturation magnetization of 0.23 emu/g at an applied field of 20 kG. All the samples demonstrated weak ferromagnetic nature, which was deduced from the M-H loops after subtracting the linear magnetization of the antiferromagnetic contribution. The Belov-Arrot plot showed a second-order magnetic transition from antiferromagnetic to ferromagnetic nature. The improvements in PVP-capped Gd-doped NiO nanoparticles are fruitful for light-emitting devices and spintronic applications.