Room-temperature confocal Raman scattering was used to probe the antiferromagnetic exchange energy J 2 between the next-nearest-neighboring Ni ions in different sized NiO nanoparticles. NiO nanoparticles were synthesized using the sol−gel method and annealed at various temperatures ranging from 300 to 800 °C. The morphology and crystal structure of the prepared samples were characterized using SEM and XRD, revealing the uniformity and development of short-range crystallinity of NiO nanoparticles. This study shows that short spin correlation leads to an exponential dependency of particle size and the existence of Ni vacancies in two-magnon excitation. The Ni vacancy concentration plays an important role in lattice expansion, along with the size reduction effect. A direct comparison between short-range magnon excitation related to the Ni vacancy concentration and NiO nonstoichiometry has been made.

Raman and photoluminescence measurements results reveal a positive Poisson ratio in strained ZnO nanoparticles, signaling the short-range electron–phonon coupling effect and an energy red-shift in the PL spectrum.