Magnetically Controlled Reflection of a Ferrofluid Cell

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Magnetically Controlled Reflection of a Ferrofluid Cell
Michael Snyder

Department of Physics and Astronomy

102 Natural Science Building

University of Louisville

Louisville KY 40292

Abstract: A novel technique for the visualization of magnetic fields. An optical ferrofluid cell is made up of two optically flat windows, or a single glass window and aluminum surface mirror with a layer of Fe3O4/Fe2O3 ferrofluid. Using different magnet configurations and lighting, highly structured pictures are obtained of applied magnetic fields. Characterized as the Magneto-Optic Kerr Effect, Optical Resonance, and Displacement Current of self assembled micrometer sized helical rods of Fe304/Fe203.

Figure 1 – A microscope slide of 10nm Fe304/Fe203 oil based Ferrofluid
Narrative: I believe that scientific papers need more of a story line in their content. The information density of a standard paper prevents most of humanity from accessing one of mankind's greatest assets. I suggest that the page of text that is written when a paper is published in the mainstream media; be included in the initial paper. For these reasons I'm including a narrative in my paper.

Our story begins with Figure #1, a smear of oil based ferrofluid on a microscope slide. There is a small chip of a permanent magnet on the slide that is not shown, but you can see some dark streaks and structure within the drops of oil.

Those dark streaks are nanoparticles of iron oxides. Specifically magnetite and hematite wrapped with electrostatic neutral surfactant to overcome attractive van der Waals and magnetic forces.
A company called Ferrotec makes this EFH1 ferrofluid and they says it typically contains by volume 5% magnetic solid, 10% surfactant and 85% carrier. One thing that I have found out by trial and error is that the magnetite slowly degrades into hematite. The exact Fe304/Fe203 ratio is not known but my best results has come from using the older ferrofluid in the 2008 year range.
Clearly, one can not see nanoparticles using a optical microscope so why can we see ordered structures in Figure #1? That my friends, is what they call the rest of the story.
"When an external magnetic field is applied to a magnetic fluid film, the particles agglomerate due to the attraction among particles, and magnetic clusters are formed. These magnetic clusters form rich structural patterns. ... With the ordered structures in the magnetic fluid film under external magnetic fields, the refractive index varies periodically over the film." - S. Y. Yang 2005

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