Finite-size effect on Neel temperature in antiferromagnetic nanoparticles

Muon spin relaxation/rotation (mu SR) 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 mu SR measurements. In the similar to 5 nm assembly, the T-N was reduced drastically to similar to 30 K, compared with the bulk T-N=229 K. 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 T-N 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.