New Materials' Odd Traits To Help Improve Computer Memory

"This type of material may eventually allow us to create non-volatile computer memory systems," says Chia-Ling Chien, professor of physics in the Krieger School of Arts and Sciences at The Johns Hopkins University. "Currently, computers use a technology called dynamic random access memory, or DRAM, and data is lost if the power supply is cut off. The new technology under development is called magnetic random access memory or MRAM, and it will be able to retain data even when power is lost."

Chien and colleagues at Brown University, IBM and the Naval Research Laboratory published a paper on their half-metallic ferromagnet, chromium dioxide (CrO2), in the June 11 issue of "Physical Review Letters."

"Half-metallic materials will also allow scientists and engineers to make superior magnetic sensors. With these sensors, more information can be stored in hard drives of computers," says Gang Xiao, professor of physics at Brown University. Xiao's lab, with help from IBM, developed the single crystal films of the new material. The secret to the potential of MRAM and other related technologies lies in harnessing spin, a characteristic of electrons that conventional electronic circuits do not use.

"Electrons have both a charge and spin, and during the last decade a new generation of technologies known as spintronic or magneto-electronic devices have begun to emerge," says Chien, director of the National Science Foundation Materials Research Science and Engineering Center at Hopkins. "These devices manipulate both the charge of electrons and their spin."

Chien cites giant magneto-resistance read-heads for hard drives as an example. "These simple spintronic devices, invented recently, were so advantageous that they're now found in practically all hard drives in computers," says Chien. Electron spin and a material's magnetic properties are linked.

The spin of each electron behaves like a tiny magnet with north and south poles, according to Chien. Scientists describe an electron's spin, and the orientation of the magnet, as "up" or "down." They use the percentage of electrons in a metal with spin up and the percentage with spin down to determine a property known as "spin polarization." Copper, for example, has zero spin polarization. Common magnets have 40 percent spin polarization.

Theorists posited the possibility of a material with 100 percent spin polarization approximately 15 years ago, Chien says, but the idea wasn't taken very seriously by scientists until the emergence of magneto-electronics in the last decade.