Size Effects on Properties of NiO Nanoparticles Grown in Alkalisalts

NiO nanoparticles with sizes of 3.5-12.4 nm were grown by thermal decomposing of nickel acetate at different temperatures in NaCl and Li2CO3 alkalisalts. The properties of the nanoparticles were characterized by X-ray diffraction spectrometer, transmission electron microscope, absorption spectrometer, micro-Raman microscope, and superconducting quantum interference device. The effects of the nanoparticle sizes on the crystal structure, exciton ground state energy, vibration modes, and magnetic properties were studied. Lattice parameter of NiO increases with a decrease in nanoparticle sizes. The band gap of NiO nanoparticles increases with a decrease in the nanoparticle size. LO modes of NiO nanoparticles shift red, and the intensity increases with a decrease in the nanoparticle sizes. Surface phonon modes are observed. Bifurcation temperature and blocking temperature of NiO nanoparticles shift to lower temperature with a decrease in nanoparticle sizes. Two peaks are present in all nanoparticles' zero-field-cooled magnetization curves, and the saturation magnetization, remanet magnetization, and coercivity increase with a decrease in the nanoparticle sizes. The nanoparticles exhibit size-dependent anomalous magnetic properties that make the remagnetization curve surpass the initial magnetization curve in the M-H hysteresis curves taken at 5 K.