Effects of dipolar interactions on the magnetic properties of γ-Fe2O3 nanoparticles in the blocked state

The role played by dipolar interactions in the coercive field and remanence of nanoparticle systems is studied using different concentrations of nearly monodisperse nanoparticles of γ-Fe2O3. The 9.0nm particles are isolated by organic encapsulation and diluted in paraffin. Magnetic properties were investigated by means of hysteresis obtained at different temperatures, zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves, and the so-called ΔM technique. The analysis of the experimental data points to the existence of a demagnetizing role played by the dipolar interaction in the coercive field.