Variations in magnetic properties caused by size dispersion and particle aggregation on CoFe2O4

Abstract

Size dispersion and particle aggregation are the key parameters that affect the magnetic properties at nanoscale due to interparticle interactions. However, few efforts have been devoted so far to understand how these parameters affect the magnetic properties of nanoparticles. Here, we experimentally demonstrate how the magnetic properties such as magnetic saturation (Ms), coercivity (Hc), Curie temperature (Tc), and blocking temperature (TB) of cobalt ferrite (CoFe2O4) nanoparticles having the same composition and near-average size are affected by size dispersion (σ) and aggregation. Cobalt ferrite nanoparticles of similar average sizes but different size dispersions and aggregations were fabricated through different synthesis routes. The results clearly demonstrate that just by reducing the size dispersion and aggregation, it is possible to modify the magnetic properties, e.g., achieving a superparamagnetic state of cobalt ferrite even under applied magnetic field as low as 100 Oe as indicated by ZFC measurements. The Stoner–Wohlfarth model with thermal agitation was used to simulate the blocking temperature of the different size dispersion and aggregation nanoparticles confirming that low size dispersion and non-aggregated particles have great influence to achieve the superparamagnetic state, especially for high coercivity materials such as cobalt ferrite.