Synthesis and magnetic properties of gold–iron–gold nanocomposites

By utilizing the sequential synthesis afforded reverse micelles, nanocomposite materials can be synthesized which have a diamagnetic core surrounded by a thin shell of ferromagnetic material passivated with a second shell of a diamagnet. Using gold as the diamagnetic material and iron as the ferromagnetic material, nanocomposites can be synthesized where there is a thin layer of the magnetic material, which is passivated and protected from oxidation. In this case, all of the spins of the magnetic layer lie within the surface of the particle. Magnetic properties were measured for nanophase particles using SQUID magnetometry. The particles, which consist of a 6 nm core of gold, coated with a 1 nm thick iron layer and passivated with an outer shell of gold, are superparamagnetic with a blocking temperature of 45 K and coercivity at 10 K of 400 Oe. These results are similar to magnetic properties of 8 nm iron particles coated with gold, where blocking temperature is 50 K and coercivity is 400 Oe. This suggests that in nanoparticles the spins that define the outer surface are responsible for the magnetic properties.