In this Comment we report a phenomenon identical to that observed in ({Y. Sun, M. B. Salamon, K. Garnier and R. S. Averback, Phys. Rev. Lett. 91, 167206 (2003)}) for systems of NiFe{2}O{4} particles (mean size ≈ 3nm) embedded in a SiO{2} matrix with two different interparticle spacings 4 nm (1) and 15 nm (2), which controls the strength of the dipolar interactions. Not only do we find the memory effect to be present in the non-interacting sample (2), indeed we find it to be {\em more} prominent than in the interacting case (1). We demonstrate that this effect can be simply attributed to a superposition of relaxation times of two sets of particles.
@article{arxiv.cond-mat/0403574,
title = {Comment on "Memory Effects in an Interacting Magnetic Nanoparticle System" by Sun et. al, prl, 91, 167206 (2003)},
author = {S. Chakravarty and A. Frydman and M. Bandyopadhyay and S. Dattagupta and S. Sengupta},
journal= {arXiv preprint arXiv:cond-mat/0403574},
year = {2007}
}