New Insights into the Magnetic Properties of CoFeO@SiO@Au Magnetoplasmonic Nanoparticles.

We report the successful synthesis and a complete magnetic characterization of CoFeO@SiO@Au magnetoplasmonic nanoparticles. The CoFeO magnetic nanoparticles were prepared using the hydrothermal method. A subsequent SiO shell followed by a plasmonic Au shell were deposited on the magnetic core creating magnetoplasmonic nanoparticles with a core-shell architecture. A spin-glass-type magnetism was shown at the surface of the CoFeO nanograins. Depending on the external magnetic field, two types of spin-glass were identified and analyzed in correlation with the exchange field acting on octahedral and tetrahedral iron sites. The magnetization per formula unit of the CoFeO core is not changed in the case of CoFeO@SiO@Au nanocomposites. The gold nanoparticles creating the plasmonic shell show a giant diamagnetic susceptibility, dependent on their crystallite sizes.