Nano wires make tiny compasses

Researchers from the University of California at Davis have built compass needles as small as 20 by 200 nanometers, which is 3,000 times narrower than a human hair and 50 times narrower than an E. coli bacterium.

The researchers' compass needles are just under half the size of the previously smallest known compasses, which occur naturally in magnetotactic bacteria that orient themselves using the earth's geomagnetic field.

The researchers' nanocompass could be used to measure magnetic fields at the nanoscale and to orient nanosized wires during the process of building molecular-sized structures; they could also be used to magnetically steer or manipulate nanostructures suspended in solution, according to the researchers.

The researchers made the device by stringing particles of magnetite, or iron oxide, on nanowires made from lithium molybdenum selenide. Each magnetite particle is as small as seven nanometers in diameter, which is seven times smaller than those found in magnetotactic bacteria. The researchers' needles are superparamagnetic at room temperature, meaning they measure stronger magnetic fields than the bacteria's compasses, which are sensitive to the earth's extremely weak magnetic field.

The researchers are working on improving the assembly and purification of their minuscule compass needles to make them consistent enough for commercial applications.

It will be two to five years before the magnetic compass can be used in advanced devices, according to the researchers.

The work was presented on April 1, 2004 at the American Chemical Society (ACS) national meeting in Anaheim, California.