Antiferromagnetic spin correlations above the bulk ordering temperature in NiO nanoparticles: Effect of extrinsic factors

Abstract

NiO has been considered one of the attractive materials for advanced technological applications such as antiferromagnetic (AF) spintronics in recent years. For a working application, an adequate knowledge of AF ordering temperature TN and spin correlations is vital. This study intends to understand extrinsic factors affecting the TN and AF spin correlations from ∼63 nm NiO nanoparticles (NPs). The micro-Raman scattering combined with neutron powder diffraction shows that NiO NPs retain T°N ∼ 523 K (similar to bulk NiO TN). The additional anomalies observed at TN' ∼ 560 K and TN'' = 669 K indicated the persistence of AF spin correlations above TN, which are suppressed relative to those observed in bulk NiO. The origin of anomalies above TN was interpreted simply as extrinsic factors such as wide distribution in the particle size and weak interparticle interaction.