Aiman - Silica coatings (typically via tetraethyl orthosilicate or silicic acid) are inexpensive and pretty commonly used methods for stabilizing magnetite nanoparticles.  They accomplish this both by increasing the least possible distance between magnetic dipoles in adjacent particles and by providing a stable electronegative surface.  Once present as a coating, the silica brings additional advantages of many commercially available silane-based crosslinkers for functionalization or vectorization of the particle.

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Best, John

Electrostatic repulsion provided by the negative charge surface of silica helps in the stabilization of magnetic nanoparticles. As already mentioned in the previous post silane coupling agents are preferred as they provide a wide range of available agents for postmodification with different functional groups.

in aqueous environment silica hydration with resulting steric stabilization plays a governing role. This is why for silica even a zero point of charge there is exceptional colloidal stability.