Spin-glass behavior in an interacting γ-Fe2O3 nanoparticle system

We investigate the superspin-glass behavior of a concentrated assembly of interacting maghemite nanoparticles and compare it to that of canonical atomic spin-glass systems. ac versus temperature and frequency measurements show evidence of a superspin-glass transition taking place at low temperature. In order to fully characterize the superspin-glass phase, the aging behavior of both the thermoremanent magnetization and ac susceptibility has been investigated. It is shown that the scaling laws obeyed by superspin glasses and atomic spin glasses are essentially the same after subtraction of a superparamagnetic contribution from the superspin-glass response functions. Finally, we discuss a possible origin of this superparamagnetic contribution in terms of dilute spin-glass models.