Low level copper-doped CoFe ₂ O ₄ has been synthesized and shows an increasing of saturation magnetization up to 6% Cu, subsequently decreasing above 6%.

In this study, a bio-derived precipitating agent/ligand, palm kernel oil, has been used as an alternative route for the green synthesis of nanoparticles of Fe-doped Co₃O₄ via the co-precipitation reaction. The palm oil was extracted from dried palm kernel seeds by crushing, squeezing and filtration. The reaction of the palm kernel oil with potassium hydroxide, under reflux, yielded a solution containing a mixture of potassium carboxylate and excess hydroxide ions, irrespective of the length of saponification. The as-obtained solution reacts with an aqueous solution containing iron and cobalt ions to yield the desired metallo-organic precursor, iron cobalt carboxylate. Characterization of the precursors by IR and gas chromatography (GC) attests to the presence of carboxylate fatty acids in good agreement with the proportion contained in the oil, and ICP confirms that the metallic ratios are in the proportion used during the synthesis. Analysis of the products thermally decomposed between 400 °C and 600 °C by XRD, EDX, TEM and ToF-SIMS, established that cobalt iron oxide nanoparticles (Co_(1−x)Fe_x)₃O₄ were obtained for x ≤ 0.2 and a nanocomposite material (Co_(1−x)Fe_x)₃O₄/Fe₃O₄ for x ≥ 0.2, with sizes between 22 and 9 nm. ToF-SIMS and XRD provided direct evidence of the progressive substitution of cobalt by iron in the Co₃O₄ crystal structure for x ≤ 0.2.

Rotten passion fruits, which are highly available in many countries during some periods of the year, can be used to efficiently produce CoFe ₂ O ₄ material with special structural and electrochemical characteristics for the hydrogen evolution reaction.