h pole in a tiny magnet. Magnetic digital data bits in a computer hard disk have magnetic states similar to the nanoparticles. When the bits get smaller as the storage density increases, the magnetic state could become unstable. To avoid data loss caused by magnetic state change from simple temperature fluctuations, computer makers need to install a high enough magnetic energy barrier to stabilize the magnetic states.

But for magnetic nanoparticles used in the body, physicians need particles with a low energy barrier to allow magnetic state to change constantly. Since magnetic opposites attract one another, the magnetic particles could potentially clump together, clogging blood flow. Rapidly changing the magnetic direction, therefore, would be essential to prevent the particles from aggregating.

"We know that the energy barriers in these magnetic nanoparticles are due to atomic-level magnetic interactions," Zhang explained. "We want to make the connection between these atomic-level interactions and the macroscopic behavior that we want in these materials."

The energy barrier between magnetic states -- which he likens to a hill that requires a certain amount of energy to climb over -- is proportional to the size of the particle as well as magnetic interactions. Zhang and his team have learned to control this energy barrier through chemical means.

Another critical property is the size. Magnetic nanoparticles for in-vivo biomedical use must be small enough to avoid detection by the immune system, yet large enough to remain in the body long enough to be circulated through the bloodstream.

And since magnetic properties vary by size, the particles must all be approximately the same diameter to ensure consistent properties. Zhang and his team have developed a statistical model to predict and control the size of the nanopartic
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Contact: John Toon
john.toon@edi.gatech.edu
404-894-6986
Georgia Institute of Technology Research News
26-Mar-2000

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