Effect of surfactants on the optical and magnetic properties of cobalt-zinc ferrite Co0.5Zn0.5Fe2O4

Nanoparticles of zinc-cobalt spinel ferrite Co0.5Zn0.5Fe2O4 (CZFO) were prepared by co-precipitation route, and the effect of the addition of various surfactants (ethanol, PEG, CTAB and acetic acid; surfactant:metals = 0.5:1) on their magnetic and optical properties were investigated. Such surfactant additives have shown great potency in controlling and improving nucleation and growth stages, leading to an optimisation of crystallite size, porosity and specific surface area (SSA). The addition of ethanol in particular helped to optimise the physicochemical properties of the material, giving the lowest crystallite size of 11.7 nm, and highest porosity and SSA values of 0.65 cm3/g and 32.37 m2/g, respectively. The sample made with ethanol also had a small grain size of 50–100 nm. The CZFO made with ethanol surfactant also had greater coercivity (Hc) and saturation magnetisation (Ms) values compared with the other surfactants, of 22 kA m−1 and 81.19 A m2 kg−1. UV–vis diffuse reflectance spectra (DRS) showed all samples made with surfactant additives had two distinct absorption edges in the visible region, around 550 nm and 700 nm. Two optical band gap (Eg) values were obtained for direct allowed transitions for these CZFO samples, with Eg1 values in the range of 1.99–2.06 eV, equivalent to that expected for ZnFe2O4, and Eg2 in the range of 1.60–1.66 eV, as expected for CoFe2O4. The CZFO made with ethanol also had the highest Eg values in both cases.