Cobalt Green Works at Room Temperature

The ability to manipulate electrons' magnetism, in addition to controlling their charge flow, has the potential to create broad new capabilities for computers and other devices and is the basis for the emerging technology "spintronics." A major barrier to creating such devices is finding nonvolatile magnetic semiconductor materials, ones that don't demagnetize easily.

So far the only materials found that meet the requirements operate only at a decidedly uncomfortable 200 degrees below zero Celsius, about minus 328 Fahrenheit. But now researchers at the University of Washington have demonstrated a material – a mixture of zinc oxide and cobalt first formulated in 1780 as a pigment called cobalt green – that appears capable of operating in more suitable environments and would allow electrons to be manipulated both electrically and magnetically.

"The breakthrough with the materials we tested is that they exhibit their magnetic properties at room temperature", said Daniel Gamelin, a UW assistant professor of chemistry.

To test cobalt green, researchers at the Pacific Northwest National Laboratory in Richland, Wash., processed zinc oxide, a semiconductor with a simple chemical structure, so a small number of zinc ions were replaced with cobalt ions, which are magnetic. Then, in Gamelin's UW lab, the cobalt ions were aligned – making the material magnetic – by exposure to zinc metal vapour, which introduces extra electrons to the zinc oxide. The magnetic properties remained strong at room temperature even when the vapour exposure ended. When the cobalt-doped zinc oxide was heated in air, the researchers observed the extra electrons dissipate and the magnetic properties disappear, in a way that demonstrated the two are interdependent.

"This work shows there is a real effect here, and there is promise for these materials," Gamelin said. "The next step is to try to get these materials to interface with silicon semiconductors."; Source: University of Washington