Structural, vibrational, magnetic, and X-ray absorption study on (Li, Zn)-doped NiO nanoparticles

Nanoparticles of Li- and Zn-doped NiO with Ni_1-x Li_xO (x = 0.01, 0.03, and 0.05) and Ni_1-x Zn_xO (x = 0.01, 0.03, 0.05 and 0.10) have been prepared by a sol–gel process. No impurity phases were found from the XRD. The average crystallite size was 10–12 nm for Li and 9–12 nm for Zn-doped NiO, respectively, from the Williamson Hall plot method. The Li-doped sample shows large magnetization 8.33 emu/g for x = 0.03 and 2 emu/g for x = 0.03 for Zn-doped NiO. The highest magnetization found in Li-doped NiO could be the creation of a large defect by doping with a monovalent dopant atom. XPS study shows the presence of Ni³⁺ and Ni²⁺ mixed valence states both in the doped sample. Further, nickel vacancies in Ni L_2,3 and hole state in the O K-edge were observed in both the doped samples from XAS measurement. The primary source of large ferromagnetism in doped NiO may be the large defect and presence of Ni³⁺ state in the doped NiO and these materials are useful for spintronic applications.