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5 October 2006


Improved magnetic-semiconductor bilayer for room-temperature spintronics

Funded by the US National Science Foundation, researchers at Ohio University and Ohio State University have created an improved magnetic-semiconductor bilayer that they claim solves a problem spintronics scientists have been invest- igating for years ("Reconstruction Control of Magnetic Properties during Epitaxial Growth of Ferromagnetic MnGa on Wurtzite GaN(0001)", Lu et al (2006) Phys. Rev. Lett. 97, 146101).

Unlike classic or vintage electronics that operate on electronic charges, spin-based electronics focuses on the spin of electrons to carry and store information. Spintronics is predicted to revolutionize the electronics industry, say the researchers, by making devices faster, improving storage capacity and reducing the amount of power needed to run them, but the technology has not yet been widely applied, because due to difficulty controlling, manipulating and measuring the electrons.

Led by postdoctoral fellow Erdong Lu, together with Arthur Smith and David Ingram, of Ohio University of Ohio University as well as J W Knepper and F Y Yang of Ohio State University, the team has created an effective interface between a semiconductor and ferromagnetic metal. Formed from binary ferromagnetic manganese gallium (MnGa) crystalline thin films epitaxially grown on wurtzite gallium nitride (0001) surfaces using RF plasma molecular beam epitaxy, the two-layer sandwich nearly eliminates any intermixing of the two layers and allows the spin to be 'tuned'.

"We found a way to grow the metal on the semiconductor. The crystalline match between the two materials was nearly perfect," said Smith, associate professor of physics and astronomy and director of Ohio University's Nano scale & Quantum Phenomena Institute. "The advantage of this finding is in the growth process. By adjusting the conditions of the growth, we can tune the spin."

The magnetic moments were found to depend on the Mn/(Mn+Ga) flux ratio and can be controlled by observation of the surface reconstruction during growth of the material. Through the monitoring process, researchers could predict
the properties of the spin.

The researchers also found that the magnetic-semiconductor bilayer will operate at room temperature. Other materials have only worked at very low temper- atures, which makes them impractical for commercial applications.