FMR and DSC study of maghemite nanoparticles in PMMA polymer matrix

Nanocomposite samples of poly(methyl methacrylate) (PMMA) polymer with a γ-Fe2O3 (maghemite) filler have been synthesised and studied by ferromagnetic resonance (FMR) and differential scanning calorimetry (DSC) methods. Two types of samples have been investigated: containing 5 wt%, 10 wt% of a maghemite filler. DSC measurements have revealed an increase in the glass transition temperature Tg and a decrease in the heat capacity cp with an increase in the concentration of nanoparticles. A FMR study in the 4–300 K temperature range has shown the presence of an asymmetric spectrum that has been analyzed in terms of two Gaussian-shaped components arising from the assumed magnetic anisotropy of the nanoparticles. The FMR investigation has exposed the temperature range of a superparamagnetic regime (60–290 K) and the blocking temperature of TB ∼ 60 K. In that range a shift in the resonance line δHr and the linewidth ΔH is related by δHr ∼ (ΔH)n, where n = 2.79 indicates a fair amount of disorder in the maghemite system. An analysis of the FMR spectra in terms of two component lines has shown the importance of the dipole–dipole interaction for higher concentrations of maghemite and for T > 220 K.