NMR-D study of the local spin dynamics and magnetic anisotropy in different nearly monodispersed ferrite nanoparticles

We present a systematic experimental comparison of the superparamagnetic relaxation time
constants obtained by means of dynamic magnetic measurements and 1H-NMR relaxometry,
on ferrite-based nanosystems with different composition, various core sizes and dispersed in
different solvents. The application of a heuristic model for the relaxivity allowed a comparison
between the reversal time of magnetization as seen by NMR and the results from the AC
susceptibility experiments, and an estimation of fundamental microscopic properties. A good
agreement between the NMR and AC results was found when fitting the AC data to a
Vogel–Fulcher law. Key parameters obtained from the model have been exploited to evaluate
the impact of the contribution from magnetic anisotropy to the relaxivity curves and estimate
the minimum approach distance of the bulk solvent.