Magnetically coupled clusters in aggregated maghemite ferrofluid: Mössbauer and magnetization study

Mössbauer spectroscopy in a weak static magnetic field and measurements of isothermal magnetization loops were used to study the effect of polymer coating of the γ-Fe ₂O₃ nanoparticles on the magnetic properties of concentrated ensembles of such nanoparticles. It was found that the individual coating of the nanoparticles by a ∼ 1 nm layer of the polymer leads to the observable changes in the shapes of the Mössbauer spectra and the magnetization curves of the ensembles. Modeling of the experimental magnetization curves in the classical Langevin model and analysis of the Mössbauer spectra in the generalized multi-level relaxation model revealed that the establishment of interparticle magnetic dipole interactions leads to both a ∼ 30 % increase in the magnetic anisotropy constant and a ∼ 35 % increase in the width of the hysteresis loop.