Young scientist finds magnetic material unnecessary spin current

Young scientist finds magnetic material unnecessary for spin current

7:42 AM, 27th July 2015
Young scientist finds magnetic material unnecessary for spin current
A young scientist found - that you don’t need a magnetic material to create spin current from insulators - this has important implications for the field of spintronics and the development of high-speed, low-power electronics that use electron spin rather than charge to carry information.

ARGONNE, US: It doesn’t happen often that a young scientist makes a significant and unexpected discovery, but postdoctoral researcher Stephen Wu of the US Department of Energy’s Argonne National Laboratory just did exactly that. What he found - that you don’t need a magnetic material to create spin current from insulators - has important implications for the field of spintronics and the development of high-speed, low-power electronics that use electron spin rather than charge to carry information.

Wu’s work upends prevailing ideas of how to generate a current of spins. “This is a discovery in the true sense,” said Anand Bhattacharya, a physicist in Argonne’s materials science division and the Centre for Nanoscale Materials (a DOE office of science user facility), who is the project’s principal investigator. “There’s no prediction of anything like it.”

Spin is a quantum property of electrons that scientists often compare to a tiny bar magnet that points either “up” or “down.” Until now scientists and engineers have relied on shrinking electronics to make them faster, but now increasingly clever methods must be used to sustain the continued progression of electronics technology, as we reach the limit of how small we can create a transistor.

To create a current of spins in insulators, scientists have typically kept electrons stationary in a lattice made of an insulating ferromagnetic material, such as yttrium iron garnet (YIG). When they apply a heat gradient across the material, the spins begin to “move” - that is, information about the orientation of a spin is communicated from one point to another along the lattice, much in the way a wave moves through water. Spin excitations known as magnons are thought to carry the current.

Wu set out to build on previous work with spin currents, expanding it to different materials using a new technique he’d developed. He worked on making devices a thousand times smaller than the typical systems used, giving him more control over the heat and allowing him to create larger thermal gradients in a smaller area. “That was the key to why we were able to do this experiment,” he says.

Wu looked at a layer of ferromagnetic YIG on a substrate of paramagnetic gadolinium gallium garnet (GGG). To everyone’s surprise, the spin current was stronger in the GGG than it was in the YIG. “The spins in the system were not talking to each other. But we still found measurable spin current. This effect shouldn’t happen at all,” said Wu.

The next step is to figure out why it does.

The scientists also want to look for other materials that display this effect. “We think that there may be other new physics working here,” said Bhattacharya. “Because, since the material is not a ferromagnet, the objects that are moving the spin are not what we typically understand.”

© Argonne National Laboratory News

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