There are two ways to modify the surface of inorganic particles. The first is accomplished through surface absorption or reaction with small molecules and the second method is based on grafting polymeric molecules through covalent bonding to the hydroxyl groups existing on the particles.

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Both type of coating will stabilize the particles. It depends upon your target application which coating you want. Importantly coating agents small orgamic molecules, polymers or other material coating such as silica will modify the magnetic properties of the original core that is magnetite nanoparticles. In general oleic acid will give you little hydrophobic and silica strongly hydrophillic magnetite nano particles.