Magnetic nanoparticles having passivated metallic cores

#This invention encompasses magnetic nanoparticles having shell/core structures and methods of sequential synthesis of said nanoparticles using reverse micelle synthesis.

#Magnetic nanoparticles based on iron, cobalt, and nickel and their alloys have been synthesized in a variety of methods including sonochemical, photochemical, as well as other solution chemical methods. Composite nanoparticles with better magnetic properties using metallic iron or cobalt have not been synthesized to be air stable. Using the reverse micelle system it is possible to form a passivation layer that makes the metallic nanoparticles oxygen resistant. This passivation layer adds functionality to the particle. For high frequency applications the particles disrupt eddy currents that limit the frequency over which magnetic metals can be used. For biomedical applications this passivation layer acts as a template for surface functionalization. As a result, the metallic nanoparticles can be used in a variety of magnetic applications from biomedical to electromagnetic devices where their magnetic properties are most desirable.

#An object of this invention is to produce magnetic nanoparticles which are oxidation resistant and having a high magnetic moment;

#FIG. 1. shows a transmission electron micrograph of the core/shell magnetic nanoparticles with an average core diameter 6.07 nm, and with a shell width 2.7 nm giving a total particle diameter 11.47 nm.

#FIG. 2. shows results of magnetization versus field experiments preformed on a Quantum Designs MPMS-5S magnetometer. The inset represents a plot of saturation versus time.

#FIG. 3. shows the preferred synthesis sequence for making the core/shell materials of this invention.

#The product of this invention consists of a metallic core of one or more metals of Group 8 and at least one passivating metal oxide shell consisting of one or more transition metals of Group 6 and/or Group 8. The particle consists of a core/shell structure less than 100 nm in diameter with cores which are 5-90 nm in diameter and shell thickness is up to about 10 nm. The products of this invention include the following:

#1. Passivated magnetic nanoparticles having a core/shell structure;

#2. A sequential surfactant assisted process;