Neutron diffraction study and superparamagnetic behavior of ZnFe2O4 nanoparticles obtained with different conditions

Spinel-type (S.G.= Fd3?m) ZnFe₂O₄ fine particles with sizes from 4 to 19 nm prepared by solvothermal and microwave-assisted solvothermal methods have been studied by neutron powder diffraction at room temperature. The cation distribution corresponding to mixed spinel structure (Zn²⁺_1−xFe³⁺_x)Fe³⁺_2−xZn²⁺_x]O₄ along with the unit cell parameter has been estimated after Rietveld refinement of the obtained neutron diffraction data for all the samples. It has been found that the inversion degree parameter (x) takes values between 0.11 and 0.20 depending not only on the particle size but also on the synthesis conditions as well. All the samples behave as superparamagnetic with an effective magnetic moment per particle (μ_SP) from 7.0×10² to 7.7×10³ μ_B. The sample obtained by microwave assistance displays a different magnetic behavior as the ZFC and FC magnetic susceptibility and the magnetization versus applied field hysteresis loop measured at 5 K suggest. This is related with the dipole interactions that are a consequence of the higher inversion degree and μ_SP.