Characterization of Magnetic Nano-Crystalline Systems

Preparation of fine magnetic particles of iron oxide is investigated Production process is based on quick chemical growth of magnetic oxide by dehydration of salt solution of Fe²⁺ and Fe³⁺ salts in different molar ratio. The STEM photographs obtained the true physical diameter of magnetic particles which is about 12 nm, and the XRD patterns is used in obtaining the D_RX, another evidence for physical diameter, that is about 9-13 nm. In order to investigate the magnetic size and susceptibility of particles, the production of magnetic oxides has been followed by ferrofluid production through dispersion of particles by surface-active agent adsorption. There was more attention given to bilayer ferrofluids with Oleate as first layer and sodium dodecyle sulfate (SDS) as second layer surfactants. The magnetic particle size, D_M, was determined through magnetic measurements by VSM system and is about 11-13 nm. The data of VSM and XRD show that D_RX is a little less, and D_M is a little greater than the true physical diameter due to the presence of surface anisotropy and the existence of a size distribution in the magnetic dispersed phase. There is a local maximum in the magnetic oxide concentration versus SDS concentration near the critical micellization concentration (CMC) of SDS, because of high tendency in making micelles after this point. The ferrofluids produced are superparamagnetic with reduced initial susceptibility of about 3×10 ^-3 - 5 × 10 ^-3 Oe ^-1. Titration by KMnO ₄ and interpretation of XRD patterns of oxides show that the closest stoichiometery of Fe₃O₄ can be achieved by increasing the Fe³⁺/Fe²⁺ molar ratio up to 2/3 with extra acidifying for prevention of uncontrolled Fe²⁺ oxidation. The adsorption of the first layer of surfactants on particles is also investigated by infrared spectroscopy. The disappearance of free Oleate peaks in IR spectrum show that to adsorb second layer, we have to make a true monolayer of Oleate by stirring the magnetic layers particles until complete separation in a solvent of Oleate has taken place.