Nanomagnets, Nanocomposite

Nanomagnets Bend the Rules: Nanocomposite materials seem to flout conventions of physics. In the latest example of surprising behavior, reported* April 15 by scientists at the National Institute of Standards and Technology (NIST) and Brookhaven National Laboratory, a class of nanostructured materials that are key components of computer memories and other important technologies undergo a previously unrecognized shift in the rate at which magnetization changes at low temperatures.

The team suggests that the apparent anomaly described as an “upturn” in magnetization may be due to the quantum mechanical process known as Bose-Einstein condensation. They maintain that, in nanostructured magnets, energy waves called magnons coalesce into a common ground state and, in effect, become one. This collective identity, the researchers say, results in magnetic behavior seemingly at odds with a long-standing theory.

The new finding could prompt a reassessment of test methods used to predict technologically important properties of "ferromagnetic" materials. The results also could point the way to marked improvements in the performance of microwave devices. Magnets are integral to these devices, used in a variety of communication and defense technologies.

Ferromagnets, including iron, cobalt, nickel and many tailor-made materials, become magnetic when exposed to an external magnetic field. As the strength of the external field increases, the materials become more magnetic, an atomic-level, temperature-influenced process called magnetic saturation. When the external field is removed, ferromagnets undergo an internal restructuring and the acquired magnetization decays, or fades, very slowly at a rate that increases with temperature.

Determined through accelerated testing methods, the temperature dependence of magnetic saturation and the rate of magnetization decay are key concerns in the design of permanent magnets, hard disks and other magnetic data storage systems.

For further information, see nist.gov/nanomagnets_bend_rules. *E. Della Torre, L.H. Bennett, and R.E. Watson, Extension of the Bloch T3/2 Law to Magnetic Nanostructrures: Bose-Einstein Condensation. Physical Review Letters. April 15, 2005.
Media Contact:Mark Bello, mark.bello@nist.gov, (301) 975-3776