Tuning the superparamagnetic effect in ZnFe2O4 nanoparticles with Mg, Ga doping

ZnFe2O4 nanoparticles are an amazing class of materials whose magnetic features are particularly appealing for the biomedical field. Their key property is the superparamagnetic behaviour at room temperature, strictly dependent on particle sizes values and cation distribution on the spinel sites, easily tuneable by substitution of dopants and by proper synthesis methods. In this paper, we focused on the undoped and Mg (on Zn site) and/or Ga (on Fe site) substituted ferrites synthesized by co-precipitation route. XRPD, SEM and Micro-Raman techniques allowed us to ensure the good quality of the samples, to determine the dopants location into spinel lattice and to estimate an average crystallite size of about 5 nm. A superparamagnetic behaviour with maxima magnetization values at room temperature between 4 and 7 emu/g at the highest applied magnetic field of 1T was disclosed, as well as a clear dependence of the blocking temperature on the cationic disorder within the two sublattices, which strengthens the magnetic interactions thus moving the transition to an ordered blocked state at higher temperatures. The electron paramagnetic resonance inspection confirmed the superparamagnetic behavior, excluding extrinsic contribution from iron oxides phases, so demonstrating that the magnetic properties depend on the inversion degree, related to the structural disorder, of the spinel phase.