Switching Magnetism On and Off

You would think that materials are either magnetic, or not. Carbon steel aligns itself in a magnetic field, while aluminum doesn't. But a group of researchers has created a semiconductor that can switch from being magnetic to nonmagnetic and back, depending on the voltage applied to it. Researchers say the discovery, reported in the 21/28 December issue of Nature, is a significant advance for materials science that could help make semiconductors even more efficient at storing and manipulating information.

For years, hard drives and floppy disks have employed magnetic materials to store data. Using a rotating electric current that induces a magnetic field, computer data could be transferred to small particles of magnetic materials, with each particle aligned either up or down, representing a one or a zero. This works well--except when a floppy disk is placed near a strong magnetic field, which aligns the particles one way, erasing all the information. If the magnetism of the floppy disk could just be temporarily turned off, scientists reasoned, information storage would be much more secure.

Hideo Ohno, a materials scientist at Tohoku University in Japan, decided to tackle this problem by investigating certain semiconductors that become magnetic at temperatures around 25 K, or -248°C. Using one of them, a manganese-doped indium arsenide, Ohno built a layered structure that became magnetic if a positive electrical charge was applied to it with a field-effect transistor. So, by keeping the temperature constant at -250°C, Ohno could switch on the magnetism by applying a positive voltage, and switch it off by applying a negative one.

"It's actually a pretty important result," says Jay Kikkawa, a physicist at the University of Pennsylvania. "Not only has Ohno demonstrated that a magnet's properties can be modified electrically, but a semiconductor magnet can easily be integrated into computer memory," adds David Awschalom, a physicist at the University of California, Santa Barbara. Awschalom says these kinds of devices could make computer crashes a nonissue, because even temporary memory that currently requires electrical power, such as RAM, could instead be magnetic. But, he says, the new magnet is still a long way from appearing in your laptop: The challenge now is to learn how to switch magnetism on and off at less frigid temperatures.

Related sites

Center for Spintronics and Quantum Computation at UCSB

Argonne National Laboratory site on magnetic memory devices