Finite-size effect on Néel temperature in antiferromagnetic nanoparticles

Muon spin relaxation/rotation (μSR) and magnetic susceptibility measurements were carried out on antiferromagnetic nanoparticles of CuO. Nanoparticles with center size of around 5 nm were prepared by ball-milling from single crystals of CuO and investigated using μSR measurements. In the ~50.3em0exnm assembly, the TN was reduced drastically to ~300.3em0exK, compared with the bulk TN=2290.3em0exK. A similar effect was observed in a system of 2 to 3 nm diameter nanorods, which was synthesized by a direct solution reaction method, where TN was suppressed further to 13 K. The present work reports direct evidence of a dramatic finite-size effect on the magnetic transition temperature in antiferromagnetic systems.