Lasers Used to Generate Electron Spin Currents
CHAMPAIGN, Ill., and EINDHOVEN, Netherlands, July 11, 2014 — Ultrashort laser pulses are being used to advance research into electron spin currents, a potential field for next-generation data storage.
Electron spin, or angular momentum, is typically random and therefore produces no spin current, which is key to operating spintronic devices. Spin currents can be driven by differences in voltage across a structure, but two separate studies show this is not necessarily the only — or even the most efficient — method.
Ultrafast laser light creates heat transport through a ferromagnet, producing an electron spin current. Courtesy of Gyung-Min Choi/University of Illinois at Urbana-Champaign.
Researchers at University of Illinois at Urbana-Champaign found that spin current can also be generated by differences in temperature. Using ultrashort laser pulses, they created temperature differences between electrons and quasiparticles known as magnons within a ferromagnet at the picosecond scale.
“Thus, we transport spin-angular momentum from magnons to electrons, and this transport leads to ultrafast spin current,” said lead researcher Gyung-Min Choi, a doctoral candidate. “We refer to this spin current as thermally driven.”
Generation of spin current at the picosecond scale is highly desirable for magnetic storage applications but difficult to achieve using electrical circuits, said Illinois professor Dr. David Cahill.
A simplified representation of Eindhoven’s new technology. A laser pulse strikes the top magnetic layer, causing electrons there to move toward the bottom layer and change the spin of electrons there. Courtesy of Eindhoven University of Technology.
The other team, at Eindhoven University of Technology, had comparable findings using ultrashort pulses to make one group of electrons exert control over the spin of another group of electrons at the femtosecond timescale. The technique could eventually allow data to be stored 1000 times as fast as existing methods, they said.
“The number of bits has been growing rapidly for many years, but the write speed has hardly increased,” said Eindhoven researcher Dr. Sjors Schellekens. “There’s a need for a new data-storage technology.”
In addition to faster data storage and information processing, this new method could also lead to development of new optical computer chips, the researchers said.
The Illinois study was funded by the U.S. Army Research Office and the U.S. Department of Energy Office of Basic Energy Sciences. The research was published in Nature Communications (doi: 10.1038/ncomms5334).
The Eindhoven study was also published in Nature Communications (doi: 10.1038/ncomms5333).
For more information, visit www.illinois.edu or www.tue.nl.
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