Magnetic relaxation process determination in the Co/Au nanoparticle system

Nonequilibrium magnetic dynamics has been investigated in the Co/Au bimetallic nanoparticle system. The system exhibits typical superparamagnetic behavior at higher temperatures and unequivocal hallmarks of magnetic relaxation process at T∼7K. Since different scenarios of magnetic transition can be hypothesized here, detailed analysis of magnetization ac and dc experimental data has been performed. Specific methods have been employed in order to reveal the nature of the examined process. The observation of critical dynamics [power-law divergence of the relaxation time at Tg; dynamic scaling of χ′′(T,f) data] and aging effects in the presence of strong interparticle interactions provide evidence that the system undergoes a transition to a super-spin-glass state rather than to a super-spin-blocked state.