Synthesis of magnetic nanoparticles using reverse micelles

Nanoparticles are single crystallites or composite materials in which the dimensions are within 1 to 100 nm in scale. Synthesizing nanoparticles with very narrow size distribution and high uniformity is one of the prime goals of this research. To achieve the high uniformity aqueous reactions are carried out using the confined aqueous core of a reverse micelle can be used as a “nano-reactor”, thus allowing us to carry on aqueous reactions, such as precipitation reactions, within a confined space and gaining the advantage of size restriction.; We present the magnetic properties of eight different nanoparticles synthesized within reverse micelles. The particles are separated into four chapters depending on their magnetic properties and structure. In chapter one we present the synthesis and magnetic properties of cobalt platinum alloys. These alloys are superparamagnetic and display higher coercivities than cobalt particles of the same size. Alloying displays one method of improving the coercivity of metal nanoparticles.; The synthesis of the antiferromagnetic KMnF₃ is presented in chapter two. The synthesis of KMnF₃ nanoparticles using reverse micelles is presented for the first time. The particles display a highly uniform cubic structure. The particles display an antiferromagnetic ordering temperature of 88 K and a blocking temperature which varies with particle size between 36 and 10 K.; Aqueous reactions allow for a greater variation of reaction conditions. In chapter three the manganese ferrite nanoparticles synthesized in reverse micelles is presented for the first time. 5 nm MnFe₂O₄ are superparamagnetic with a blocking temperature of 33 K. For comparison two other common ferrites, Fe₃O₄ and CoFe₂O ₄, were also synthesized. Reaction conditions demonstrated an effect on the overall cation distribution between the A and B sublattice of the spinel. This redistribution did not have a pronounced affect on magnetic properties.; Lastly, a sequential synthesis is presented where iron and gold are grown in coreshell and “nano-onion” like structures. These particles have the favorable magnetic properties of iron while remaining protected from oxidation by a gold shell. The effect of the gold shell on the magnetic properties of coercivity and blocking temperature is discussed. Although the thickness of the gold shell is varied between 2 and 3 nm, there is not a change in the coercivity or blocking temperature within experimental error. In addition, the electronic properties of the “nano-onions” were studied. Gold-Iron-Gold nano-onions display a −1.5% magnetoresistance. The particles undergo a transition from itinerate to localized electrons resulting in a 400% increase in resistance as the particles are cooled to 10 K.