We have successfully synthesised and studied the bilayer ferrofluids with sodium oleate C18H33O2-Na+ as the first layer and sodium dodecyle sulfate C12H25Na+SO-4 (SDS) as the second layer surfactants. The solid phase of the ferromagnetic colloidal system was formed based on quick chemical growth. The adsorption of oleate molecule on the surface of the solid solution has been investigated by IR spectroscopy. The XRD analysis of the oxides and titration by KMnO4 show that the closest

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... of Fe3O4 is achieved by the increase of Fe3+/Fe2+ molar ratio up to 2/3 with extra acidifying for prevention of uncontrolled Fe2+ excitation. The X-ray diffraction and magnetic measurements by VSM were employed for determining the particle magnetic and crystal sizes. The particle size was determined to be 9-13 nm. The magnetisation measurement of the ferrofluid indicate a saturation magnetisation of about 1.5 emu/g and reduced initial susceptibility of 6 10-3 Oe-1, which are the proper values for a superparamagnet. However, the saturation magnetisation shows a local maxima at SDS concentration about 0.07M, which is different from the behaviour presented by the mono-layer ferrofuids.