SAN FRANCISCO—A new technique used by researchers to investigate the ferromagnetic properties of materials could be a key step on the road to spintronics, a futuristic concept in which data is processed on the basis of electron “spin” rather than charge.
Researchers led by scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory used the technique, known as Harpes, to investigate the bulk electronic structure of the prototypical dilute magnetic semiconductor gallium manganese arsenide. Their findings show that the material’s ferromagnetism arises from both of the two different mechanisms that have been proposed to explain it.
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Harpes stands for hard x-ray angle-resolved photoemission spectroscopy. The technique, based on the photoelectric effect described in 1905 by Albert Einstein, enables scientists to study bulk electronic effects with minimum interference from surface reactions or contamination. It also allows them to probe buried layers and interfaces that are ubiquitous in nanoscale devices, and are considered key to smaller logic elements in electronics, novel memory architectures in spintronics and more efficient energy conversion in photovoltaic cells, according to Berkeley Labs.
With the Harpes technique, a beam of hard x-rays flashed on a sample causes photoelectrons from within the bulk to be emitted. Measuring the kinetic energy of these photoelectrons and the angles at which they are ejected reveals much about the sample’s electronic structure.
Credit: Alex Gray
"This study represents the first application of Harpes to a forefront problem in materials science, uncovering the origin of the ferromagnetism in the so-called dilute magnetic semiconductors," said Charles Fadley, the physicist who led the development of Harpes. "Our results also suggest that the Harpes technique should be broadly applicable to many new classes of materials in the future."