Memory effects in an interacting magnetic nano-particle sample

The non-equilibrium dynamics in a Fe-C nano-particle sample, showing a low- temperature spin-glass-like phase, have been studied by low-frequency AC-su sceptibility experiments. A temporary stop in the cooling during an AC-susc eptibility measurement yields a decrease of chi with time. Upon the followi ng re-heating chi traces the previous curve with a dip at the temperature w here the stop occurred. This effect has recently been discovered and discus sed for different spin-glass systems, but has never been detected before in a nano-particle system. (C) 2000 Elsevier Science B.V. All rights reserved .