  We report studies on temperature, field and time dependence of magnetization
on cupric oxide nanoparticles of sizes 9 nm, 13 nm and 16 nm. The nanoparticles
show unusual features in comparison to other antiferromagnetic nanoparticle
systems. The field cooled (FC) and zero field cooled (ZFC) magnetization curves
bifurcate well above the N\'eel temperature and the usual peak in the ZFC
magnetization curve is absent.
  The system does not show any memory effects which is in sharp contrast to the
usual behavior shown by other antiferromagnetic nanoparticles. It turns out
that the non-equilibrium behavior of CuO nanoparticles is very strange and is
neither superparamagnetic nor spin glass-like.

Mesoscale and Nanoscale Physics