16 MARCH 2006
does
matter, and smaller is better.
Well, maybe not for everything. But when it comes to magnetism, smaller and
smaller means stronger and smarter. And scientists have just begun to
exploit the magnetic potential in the science of the ultrasmall.
That's the science of the nanoworld, where size is measured in billionths of a meter, or nanometers. A nanometer really is very small -- enlarging it to a meter would be like making a marble the size of the Earth.
Once, not so long ago, the nanorealm was ruled by science fiction. But now
nano-nonfiction proliferates in real-world scientific journals. Hundreds
of papers a month appear describing nanoscience studies of everything
from superstrong materials to superfast computers.
One of the least publicized but most relevant realms of real-world nanoscience is the study of nanomagnetism. It's not exactly about making magnets that are too small to see; it mainly involves applying nanoknowledge to designing magnets with fruitful uses -- such as for saving energy, improving computer memory and enhancing homeland security.
"The field [of nanomagnetism] is veritably bursting with activity and cross-disciplinary innovation," writes physicist Samuel Bader of Argonne National Laboratory in Illinois.
For instance, today's strongest permanent magnets are made from a material discovered in 1984, containing neodymium, iron and boron. Magnets made using nanotechniques could be even stronger. The old material could be made more powerful, for instance, by building it into a composite with another component made of pure iron or cobalt. If the two layers of the composite are confined closely enough -- within a few nanometers -- the strength of the magnetism per amount of material is greatly enhanced. Even stronger magnets might be made using newer materials fabricated by nanotechnology.
"Nanoscience offers the possibility to create and deliver ultrastrong permanent magnets," Bader asserts in a recent issue of Reviews of Modern Physics. Those new magnets could be used to make smaller and more efficient motors. "Lighter weight motors could save fossil fuels in auto and air transportation," he says. "Electric motors for hybrid automotive vehicles might become a major market soon."
Computers might also save energy with help from nanomagnetism. Magnetism is all about the spinning of electrons, the subatomic particles that encase all atoms with a negative electrical charge. Conventional computers use the electron's charge to store and manipulate information. Nanomagnetism research, though, is fast on track for using the electron's spin for computing purposes. Entirely new kinds of transistors now in development can use the direction of an electron's spin to represent the 1s and 0s of computer language.
A computer based on "spintronics" could boot up instantly, with all the necessary information stored in "spin" memory. And computers based on spintronics might use much less energy -- and consequently generate less heat -- than today's thigh-frying laptops.
"We know that for today's electronics, heat management is an important issue," says Bader. "Stated more dramatically, one can hardly rest a laptop on one's lap because of the heat generated."
Besides that, nanomagnetism could boost the amount of memory storage available on a given size of memory chip. Today's best chips store about 100 billion bits per square inch; current methods don't seem able to do much better. "In order to advance to trillions of bits per square inch and beyond, new approaches are required, and nanomagnetism might provide what is needed," Bader declares. Several nanotech strategies for achieving that goal are now being tested.
Beyond the commercial benefits to the computer industry, nanomagnetism offers possible homeland security benefits, too -- by mixing a little biology in with the physics and chemistry. Nanotechniques under development can wash a virus's DNA out from inside its protective outer shell. The hollow shell can then be chemically induced to swallow magnetic particles of iron or cobalt. For one virus in particular, the bacteria-attacking T7, the resulting "magnet" would be about 40 nanometers across.
"Such magnetic virus particles can serve as the basis for exotic sensing schemes," Bader notes. The virus's shell is made of numerous protein molecules that offer "docking ports" for attaching to various other molecules. Molecules to be attached can be chosen based on their ability to stick to specific toxic molecules. The resulting package is like a magnetic drug-sniffing dog that can detect toxic molecules such as those that might be deployed by bioterrorists. Sensing such toxic substances would be rapid and accurate because of the ease of detecting the magnetism of the particles trapped inside the shell.
"A rich variety of possibilities exist in the study of protein coated magnetic nanoparticles of varying sizes," Bader writes. "The outlook is very promising for this interdisciplinary endeavor that represents a marriage between magnetism and biology."
It just goes to show that there are some marriages where smaller really is better.
E-mail: tsiegfried@nasw.org
