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Brief: Researcher Says Pigment Could Work As Memory

A mixture of zinc oxide and cobalt could form a magnetic thin film in a future nonvolatile memory.
LONDON — 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, could be used to form a magnetic thin film in a future nonvolatile memory.

"The big challenge is to develop materials that can perform these kinds of functions not just at cryogenic temperatures but at practical temperatures," said Daniel Gamelin, a University of Washington assistant professor of chemistry, in a statement. "The breakthrough with the materials we tested is that they exhibit their magnetic properties at room temperature."

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 vapor, which introduces extra electrons to the zinc oxide. The magnetic properties remained strong at room temperature even when the vapor 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."

The bluish-green mixture of zinc oxide and cobalt, called cobalt green or Rinman's green, was first devised as a painter's pigment by Swedish chemist Sven Rinman.