Memory effect and super-spin-glass ordering in an aggregated nanoparticle sample

A system consisting of aggregated nonstoichiometric zinc ferrite nanoparticles has been studied using AC and DC magnetization measurements. A superparamagnetic-super-spin-glass phase transition at T-g has been identified. The relaxation time diverges at T-g and the nonlinear susceptibility shows an abrupt increase. The critical behavior vanishes when,the nanoparticles are not in close contact. The observation of the memory effect identical to that which has been already discovered in canonical spin-glass supports the existence of a true thermodynamic transition in agglomerated magnetic, nanoparticles. (C) 2003 Elsevier B.V. All rights reserved.