The influence of the starch coating on the magnetic properties of nanosized cobalt ferrites obtained by different synthetic methods

[Display omitted] •Nanostructured cobalt ferrites' magnetic properties.•“Janus effect” of starch coating on cobalt ferrite magnetization.•Co-precipitation and hydrothermal methods/starch coating – increased magnetization.•Mechanochemical and microemulsion methods/starch coating – decreased magnetization. To investigate the magnetic behavior of starch-coated cobalt ferrites, well-established synthetic methods, i.e., coprecipitation, mechanochemical, ultrasonically assisted coprecipitation, microemulsion, and microwave-assisted hydrothermal syntheses were chosen for their preparation. The obtained materials had pure single-phase spinel structures. Scanning and transmission electron microscopy analyses revealed that the morphology of the samples is not uniform, and particle aggregation is a dominant process. Fourier transform infrared spectra and thermogravimetric analysis confirmed the presence of starch in all–coated samples. The unusually higher saturation magnetization of starch-coated samples than their as-prepared analogs, obtained by coprecipitation, ultrasonically assisted coprecipitation, and microwave-assisted hydrothermal methods, might be explained by the Ostwald ripening mechanism induced by the coating process. A decrease in magnetization was noticed for the starch-functionalized nanomaterials synthesized by mechanochemical and microemulsion methods, in comparison to their as-prepared analogs, i.e., the size distribution of such nanoparticles is narrow, and the average diameter of the grains is near critical for the Ostwald ripening process.