The effect of microstructural features on the ferromagnetism of nickel oxide nanoparticles synthesized in a low-pressure arc plasma

Nickel oxide nanoparticles were first synthesized by sputtering high-purity nickel in an oxygen plasma of a low-pressure arc discharge. The structure, morphology, and optical and magnetic properties of NiO nanoparticles were studied by XRD, TEM, FTIR, UV-VIS, and VSM. TEM images showed that the obtained NiO nanoparticles have a narrow particle size distribution and an average particle size of 12 nm. The XRD results and the processing of diffractograms by the Rietveld method showed that the obtained nanoparticles have a face-centered cubic lattice with an average particle size of 13 nm. With decreasing temperature, residual stresses increase and peaks corresponding to the superstructure appear. The band gap of NiO was determined from the optical absorption spectrum and amounted to 3.21 eV. Magnetic measurements showed that, at temperatures of 200 and 300 K, NiO nanoparticles, unlike bulk particles, exhibit ferromagnetic behavior, and at 5 K a magnetic hysteresis loop appears. Based on the studies, a dendritic model of the nanoparticle microstructure is proposed.