Hydrothermal Growth of Magnetic Iron Oxides

Evy Colon-garcia, Clemson University


Fundamental iron oxides such as Fe3O4, Y3Fe5O12 (YIG), YFeO3 and other derivatives are fascinating materials because of their ferrimagnetic properties and potential uses in optical and microwave communication devices and biomedical applications. Although the ferrimagnetic properties of these materials are well-known1 valuable details about their microscopic magnetic structure have not been extensively studied. Neutron diffraction can be used to elucidate these microscopic magnetic crystal structures since neutrons possess a spin which causes an interaction with magnetic moments around them, including the ones arising from the electron cloud of an atom.2 However, neutron diffraction is particularly challenging because it requires crystals of very high purity and in excess of 1cm in size. With new neutron sources, such as the Spallation Neutron Source at Oak Ridge National Laboratories, this size is no longer necessary since it can be used to collect magnetic structural data on crystals which are only 2mm in size. This will make single crystal neutron diffraction a more routine means of characterization and greatly improve our understanding of even fundamental magnetic structures.
In the past flux methods were the preferred synthetic method to obtain many iron oxides, however the presence of PbO vapors makes it a hazardous procedure. Hydrothermal synthesis, crystal growth in aqueous solutions at high temperatures and pressures3,4, appears to be an ideal route to these materials since it eliminates the toxicity of PbO and it is performed at much lower temperatures than traditional crystal growth methods. As such it enables the growth of crystals with less thermal strain, fewer defects, and can be used to synthesize compounds with high melting points (such as YIG with a melting point of 1555¡C) or which melt incongruently. This project presents a descriptive hydrothermal synthetic study of iron bearing single crystals for new single crystal neutron diffraction studies as well as for use as substrates for polymeric biomedical applications. In particular, single crystals of Fe3O4, Y3Fe5O12 as well as other rare earth analogues have been synthesized as fairly large single crystals in aqueous base at 580¡C and 20kpsi and characterized using powder x-ray diffraction, single crystal x-ray diffraction and energy dispersive x-ray analysis. The synthesis of other ferrites such as Barium Ferrites and yttrium and rare earth orthoferrites as well as the study of descriptive chemistry in these systems is presented.
1. OstorŽro, J. et al Journal of Alloys and Compounds 221 (1995) 193-196
2. West, A.R. Basic Solid State Chemistry. 1999
3. Rabenau. Angew. Chem. Int. Ed. 24 (1985) 1026-1040
4. R. A. Laudise. Chem. Engin. News 1987, September 28, 30-43