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Spintronics specialists tailor GaAs with manganese

Managanese-doped GaAs could lead to chips that can both manipulate and store data.

A team of researchers from three US universities has manipulated GaAs using a scanning tunnelling microscope (STM) to create magnetic semiconductor material that could find a use in future spintronic devices.

"The ability to tailor semiconductors on the atomic scale is the holy grail of electronics and this method may be the approach that is needed," said Ali Yazdani of Princeton University.

"Up until now we have not had a way to control how the manganese sits in the gallium arsenide substrate. We could not specify, for example, how large the bits of manganese would be or how far apart they would be located."

Previously, manganese-doped GaAs has had a ferromagnetic transition temperature of -88°C. But if the material is to be useful in electronics applications it must remain magnetic at room temperature. By studying the effect of introducing the manganese atoms at specific locations the researchers hope to optimize the material s properties.

"The important thing technically was that we could incorporate the manganese into the underlying crystal lattice," said Yazdani. "If you want to study how the semiconductor functions, it would not have been enough merely to deposit the manganese on the surface. They needed to become a single integrated material."

Yazdani and colleagues at the University of Iowa and the University of Illinois at Urbana-Champaign used the STM to study interactions between manganese atoms they had introduced into the lattice and the electronic states of the surrounding gallium and arsenic atoms. They found that the ferromagnetic interaction depended strongly on crystallographic orientation.

The researchers hope to exploit this effect by growing oriented manganese-doped GaAs crystals to enhance the ferromagnetic transition temperature. They also believe that the STM technique could provide a realistic approach for "creating precise arrangements of single spins as coupled quantum bits for memory or information processing purposes".

Liz Kalaugher is the editor of Nanotechweb.

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