Thermal variation of the relaxation time of the magnetic moment of $\gamma$-${\mathrm{Fe}}_2$${\mathrm{O}}_3$ nanoparticles with interparticle interactions of various strengths

The dynamical properties of $\gamma$-${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ particles, dispersed in a polymer, were investigated by ac susceptibility ($2\times {10}^{-2\mathrm{}} \mathrm{Hz}<~\nu <~{10}^4\mathrm{Hz}$) and Mössbauer spectroscopy measurements. The variation of the average blocking temperature as a function of the measuring time is satisfactorily described by a model which accounts for interparticle interactions by a statistical calculation of the dipolar energy for a disordered assembly of particles with a volume distribution and easy axes in random position.