While attempting to solve one mystery about iron oxide-based nanoparticles, a research team working at the National Institute of Standards and Technology (NIST) stumbled upon another one. But once its implications are understood, their discovery* may give nanotechnologists a new and useful tool.
The nanoparticles in question are spheres of magnetite so tiny that a few thousand of them lined up would stretch a hair's width, and they have potential uses both as the basis of better data storage systems and in biological applications such as hyperthermia treatment for cancer. A key to all these applications is a full understanding of how large numbers of the particles interact magnetically with one another across relatively large distances so that scientists can manipulate them with magnetism.
"It's been known for a long time that a big chunk of magnetite has greater magnetic 'moment'think of it as magnetic strengththan an equivalent mass of nanoparticles," says Kathryn Krycka, a researcher at the NIST Center for Neutron Research. "No one really knows why, though. We decided to probe the particles with beams of low-energy neutrons, which can tell you a great deal about a material's internal structure."
The team applied a magnetic field to nanocrystals composed of 9 nm-wide particles, made by collaborators at Carnegie Mellon University. The field caused the particles to line up like iron filings on a piece of paper held above a bar magnet. But when the team looked closer using the neutron beam, what they saw revealed a level of complexity never seen before.
"When the field is applied, the inner 7 nm-wide 'core' orients itself along the field's north and south poles, just like large iron filings would," Krycka says. "But the outer 1 nm 'shell' of each nanoparticle behaves differently. It also develops a moment, but pointed at right angles to that of the core."
In a word, bizarre. But potentially useful.
|Contact: Chad Boutin|
National Institute of Standards and Technology (NIST)