Abstract
We have investigated properties of systems of strongly interacting magnetic nanoparticles in order to estimate the influence of the inter-aggregate interactions on the collective phenomena. We have compared two systems composed of gamma-Fe2O3 nanoparticles, prepared by thermal decomposition of an organic precursor and coprecipitation, respectively; with those prepared by coprecipitation, containing the particle aggregates coated by SiO2 layer of different thickness.
Detailed magnetic studies of all samples such as the temperature dependence of magnetization and frequency-dependent a.c. susceptibility, recorded also in external magnetic field, revealed the blocking temperature close to 300K and super-spin glass (SSG) or SSG-like nature of the systems. The slight minimization of the interaction strength in the system with increasing thickness of the SiO2 coating has been observed.