**2.2. Experiments from pure and doped zinc ferrites obtained by microwave-assisted combustion method**

We focused on the microwave combustion synthesis method of Ca (on Zn site) and Gd (on Fe site) substituted ferrites. Undoped ZnFe2 O4 and Sr, and Al doped samples were also synthesized and used for comparison. All the samples have been investigated by X-ray powder diffraction and SEM-EDX analyses as a complement of Raman results. The magnetic behavior has been measured by SQUID magnetometry. All the experimental details are reported elsewhere [59].

We found, for all the samples, a superparamagnetic behavior with saturation magnetization between 6 and 10 emu/g at the maximum applied magnetic field of 3 T, with a more effective role played by Ca ions with respect to Gd ions substitution.
