One-pot synthesis of CoFe–Fe3O4 nanocomposites with tunable magnetic properties and long term stability

• Uniform CoFe–Fe3O4 nanocomposites with variant Co/Fe molar ratios were synthesized.
• The obtained nanocomposites have high saturation magnetization values.
• The saturation magnetization values can be tailored from 60 to 158 emu/g(Fe+Co).
• The obtained CoFe–Fe3O4 NPs exhibit superior long term magnetic stability in air.

In this work, uniform CoFe–Fe3O4 nanocomposites with variant Co/Fe molar ratios were synthesized through a facile one-pot method for the first time by thermal decomposition process in mixed solvents of 1-octadecene and oleic acid. The obtained magnetic nanoparticles were characterized by using TEM, HRTEM and XRD in details. The Co/Fe molar ratios in the final CoFe–Fe3O4 nanocomposites can be well tuned by the Co/Fe molar ratios in the reaction precursors. The obtained CoFe–Fe3O4 nanocomposites have high saturation magnetization values (up to 158 emu/g(Fe+Co)) and soft ferromagnetic properties (low coercivity, 338 Oe) at room temperature. The saturation magnetization values can be tailored from 60 to 158 emu/g(Fe+Co) by changing the Co/Fe molar ratios in the reaction precursors from 0 to 0.2. The magnetization value of CoFe–Fe3O4 NPs remains 118 emu/g(Fe+Co) after being exposed in the air for four months at room temperature, indicating its superior long term magnetic stability.

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