Microstructure, porosity and magnetic properties of Zn0.5Co0.5Fe2O4/SiO2 nanocomposites prepared by sol-gel method using different polyols

The study reports the influence of polyols (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol) used in the synthesis on the structure and magnetic properties of Zn0.5Co0.5Fe2O4/SiO2 nanocomposites. The Xray diffraction patterns indicated the formation of poorly to highly crystalline Zn0.5Co0.5Fe2O4, together with several other crystalline phases (Zn2SiO4, Co2SiO4, SiO2, Co3O4, ZnO), depending on the used polyol and annealing temperature. The Fourier transformed infrared spectra confirmed the formation of metal oxide bonds in Co-Zn ferrite and of SiO2 matrix. The physical density increases and the X-ray density decreases with average crystallite size decrease. The transmission electron microscopy measurements revealed the spherical nanoparticles (2-47 nm) size growth with increasing distance between the hydroxyl groups and number of hydroxyl groups. The shape of the hysteresis loops suggests the dependence of the magnetic behaviour on the structural properties, and consequently, on the polyol structure and the annealing temperature. Also, the saturation magnetization (M-s, similar to 15.8-61.0 emu/g), remanent magnetization (M-R similar to 0.41-9.5 emu/g) and coercive field (H-c similar to 0.014-0.021 T) of Zn0.5Co0.5Fe2O4 increase with the polyol chain length and hydroxyl group number. Both Ms and Hc increase with increasing crystallite size. The shape of the magnetization derivative curves with respect to the applied magnetic field indicates the presence of a single magnetic phase (Zn0.5Co0.5Fe2O4) that has ferromagnetic or superparamagnetic type behaviour, depending on the annealing temperature.