Short-Range Magnon Excitation in NiO Nanoparticles

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 degrees 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.