Reversible post-synthesis tuning of the superparamagnetic blocking temperature of γ-Fe2O3nanoparticles by adsorption and desorption of Co(ii) ions

Abstract

The influence of the post-synthesis adsorption of Co(II) ions on the structural and magnetic properties of maghemite (γ-Fe₂O₃) nanoparticles with a mean particle size of about 10 nm has been investigated. It is shown that the step-wise adsorption of Co(II) can controllably increase the blocking temperature, T_B, of the system up to 60 K with respect to that of untreated particles, while neither the particle size nor the particle size distribution are significantly modified. This is accompanied by a four-fold increase in the coercivity, H_C, at low temperatures. Using a selective leaching of the previously adsorbed Co(II) ions the T_B and H_C values of the pristine γ-Fe₂O₃ nanoparticles are recovered. Hence, a reversible and controllable tailoring of the magnetic properties (e.g., T_B and H_C) of the γ-Fe₂O₃ nanoparticles can be achieved by a simple adsorption and desorption process of Co(II) ions after their synthesis.