Microwave assisted hydrothermal synthesis of (Fe,Co)3O4 nanoparticles in the presence of surfactants and effects of Co/Fe ratio on microstructure and magnetism

Microstructure and magnetic properties of nanoparticles can be tailored by optimising the synthesis procedure and changing chemical composition. In this study, a two-step procedure, i.e., coprecipitation in the presence of PEG 300 followed by microwave assisted (MW) hydrothermal synthesis, was introduced to obtain CoxFe3-xO4 (x = 0, 0.1 and 0.2) nanoparticles. It was found that with the increase of Co content, particle/crystallite size increased, with significant change of coercivity (Hc). The mixed samples of CoxFe3-xO4 (x = 0.1 and 0.2) were magnetically harder in comparison with Fe3O4. Тhe Hc of Fe3O4 was 91 Oe, while for Co0.10Fe2.90O4 and Co0.20Fe2.80O4, Hc was 256 Oe and 1070 Oe, respectively. Saturation magnetisation (Ms) of mixed samples also increased up to 6% compared to Fe3O4. A special effort was devoted to study the effects of introducing different surfactants (PEG 300, PEG 4000 or SDS) during the synthesis procedure in order to improve morphological and microstructural properties of CoFe2O4 nanoparticles. The influence of surfactants on physical/chemical properties of nanoparticles is discussed.