NANOSCALE MAGNETIC PARTICLES - NEW METHODS TO SURFACE PROTECTED METALLIC AND IMMISCIBLE BIMETALLIC CLUSTERS PARTICLES

The metal vapour-solvent low temperature matrix method has been used t o prepare nanoscale iron powders. The morphology of the fine particles was characterized using transmission electron microscopy. Crystallite and particle sizes were determined via XRD and BET techniques. The ma gnetic properties of the powders were investigated using Mossbauer spe ctroscopy and SQUID magnetometry. X-ray photoelectron spectroscopy was used to probe the surface of the fine particles. The use of a non-pol ar solvent (hexane) to trap the atoms resulted in air-sensitive iron p owders with some incorporation of carbon and hydrogen. Crystallite siz es of approximately 5 nm were observed and these systems behaved super paramagnetically at room temperature. The powders were easily oxidized to alpha-Fe2O3. Codeposition of iron with perfluorotri-n-butyl-amine (PFTA) resulted in the formation of FeF2 as the major product. Reduced values of T(N) and theta(c) were observed for FeF2 phase. The fine po wders were found to be air and moisture sensitive forming FeF3, FeF3.H 2O and gamma-Fe2O3 upon exposure to air. The bimetallic system of immi scible metals, Fe and Ag, was investigated by co-deposition of these m etals with pentane. Separate phases of Ag and Fe were observed to be i n these powders. Mossbauer investigations indicated that isolated iron atoms accounted for 5-27% of the iron present indicating some solid s olubility of these two metals. Enhanced hyperfine fields were observed for the iron clusters. Fe3O4, formed during handling of the powders, had reduced hyperfine fields for both A and B sites as well as reduced Verwey transition temperatures. Iron powders prepared in pentane and trapped with 1-dodecanethiol exhibited unique behaviour after heat tre atment. Small iron particles with a coating of FeS were formed after h eat treatment at 300-600-degrees-C for 2 h under argon. Air sensitivit y of the powders was greatly reduced after the formation of the sulphi de surface layer. The possible existence of exchange interactions betw een the two phases was investigated using magnetic measurements and wa s found to be small but significant. These experiments demonstrate tha t metal atom clustering in low temperature matrices, followed by trapp ing/ligation and or heat treatment can yield a variety of new nanoscal e materials. Crystallite sizes and outer coating material can be contr olled and manipulated. Immiscible bimetallic particles, core-shell str uctures, and many other unique phases are attainable.