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How to merge manganese with GaN for spintronics

To bind gallium nitride with manganese, scientists have used the nitrogen polarity of GaN and heated the sample
Ten years ago, scientists were convinced that a combination of manganese and GaN could be a key material to create spintronics. This field refers to the next generation of electronic devices that operate on properties found at the nanoscale.

But researchers grew discouraged when experiments indicated that the two materials were as harmonious as oil and water.

Now, a new study led by Ohio University physicists suggests that scientists should take another look at this materials duo, which was once heralded for its potential to be the building block for devices that can function at or above room temperature.

"We've found a way - at least on the surface of the material - of incorporating a uniform layer," says Arthur Smith, a professor of physics and astronomy at Ohio University who leads the international collaboration of Argentinian and Spanish researchers.

The scientists made two important changes to create the material merger, which they report in the journal Physical Review B. First, they used the nitrogen polarity of GaN, whereas conventional experiments used the gallium polarity to attach to the manganese, Smith explained. Second, they heated the sample.

At temperatures less than 105oC, the manganese atoms "float" on the outer layer of gallium atoms. When the scientists raised the temperature about 100oC, Smith says, the atoms connected to the nitrogen layer underneath, creating a manganese-nitrogen bond. This bond remains stable, even at very high temperatures.

The theoretical scientists accurately predicted that a "triplet" structure of three manganese atoms would form a metastable structure at low temperatures, Smith says. But at higher temperatures, those manganese atoms break apart and bond with nitrogen.

Image showing a 3D rendering of a stable manganese gallium nitride surface structure (Credit: A.R. Smith, Ohio University)

Valeria Ferrari of the Centro Atómico Constituyentes points out her group performed quantum mechanical simulations to test which model structures have the lowest energy, which suggested both the trimer structure and the manganese-nitrogen bonded structure.

Now that scientists have shown that they can create a stable structure with these materials, they will investigate whether it has the magnetic properties at room temperature necessary to function as a spintronic material.

Further details of this work have been published in the paper, " Manganese 3×3 and √3×√3-R30∘structures and structural phase transition on w-GaN(0001̅ ) studied by scanning tunneling microscopy and first-principles theory," by A. V. Chinchore et al in Physical Review B, 87, 165426 (2013).

DOI: 10.1103/PhysRevB.87.165426

This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (STM studies of nanoscale spintronic nitride systems), the National Science Foundation (advancing nanospintronics through international collaboration), CONICET, ANPCyT and Spanish MICINN. The Ohio Supercomputing Centre provided computer time.

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