  We study magnetic relaxation dynamics, memory and aging effects in
interacting polydisperse antiferromagnetic NiO nanoparticles by solving a
master equation using a two-state model. We investigate the effects of
interactions using dipolar, Nearest-Neighbour Short-Range (NNSR) and Long-Range
Mean-Field (LRMF) interactions. The magnetic relaxation of the nanoparticles in
a time-dependent magnetic field has been studied using LRMF interaction. The
size-dependent effects are suppressed in the ac-susceptibility, as the
frequency is increased. We find that the memory dip, that quantifies the memory
effect is about the same as that of non-interacting nanoparticles for the NNSR
case. There is a stronger memory-dip for LRMF, and a weaker memory-dip for the
dipolar interactions. We have also shown a memory effect in the
Zero-field-cooled magnetization for the dipolar case, a signature of glassy
behaviour, from Monte-Carlo studies.
