A New Spin on Electronics

Estimated reading time: 6 minutes

A University of Utah-led team has discovered that a class of “miracle materials” called organic-inorganic hybrid perovskites could be a game changer for future spintronic devices. 

Spintronics uses the direction of the electron spin — either up or down — to carry information in ones and zeros. A spintronic device can process exponentially more data than traditional electronics that use the ebb and flow of electrical current to generate digital instructions. But physicists have struggled to make spintronic devices a reality. 

The new study, published online today in Nature Physics, is the first to show that organic-inorganic hybrid perovskites are a promising material class for spintronics. The researchers discovered that the perovskites possess two contradictory properties necessary to make spintronic devices work — the electrons’ spin can be easily controlled, and can also maintain the spin direction long enough to transport information, a property known as spin lifetime.

PHOTO CREDIT: University of Utah

Sarah Li (left) and Z. Valy Vardeny (right) of the Department of Physics & Astronomy at the University of Utah discuss the ultrafast laser used to prepare and measure the direction of the electron spin of hybrid perovskite methyl-ammonium lead iodine (CH3NH3PbI3). They are the first to show that organic-inorganic hybrid perovskites are a promising material class for spintronics, an emerging field that uses the spin of the electron to carry information, rather than the electronic charge used in traditional electronics.

“It’s a device that people always wanted to make, but there are big challenges in finding a material that can be manipulated and, at the same time, have a long spin lifetime,” says Sarah Li, assistant professor in the Department of Physics & Astronomy at the U and lead author of the study. “But for this material, it’s the property of the material itself that satisfies both.” 

The miracle material 

Organic-inorganic hybrid perovskites is already famous in scientific circles for being amazingly efficient at converting sunlight into electricity.

“It’s unbelievable. A miracle material,” says Z. Valy Vardeny, distinguished professor in the Department of Physics & Astronomy and co-author of the study, whose lab studies perovskite solar cells. “In just a few years, solar cells based on this material are at 22 percent efficiency. And now it has this spin lifetime property. It’s fantastic.” 

The material’s chemical composition is an unlikely candidate for spintronics, however. The hybrid perovskite inorganic frame is made of heavy elements. The heavier the atom, the easier it is to manipulate the electron spin. That’s good for spintronics. But other forces also influence the spin. When the atoms are heavy, you assume the spin lifetime is short, explains Li. 

“Most people in the field would not think that this material has a long spin lifetime. It’s surprising to us, too,” says Li. “We haven’t found out the exact reason yet. But it’s likely some intrinsic, magical property of the material itself.” 

Spintronics: That magnetic moment when… 

Cellphones, computers and other electronics have silicon transistors that control the flow of electrical currents like tiny dams. As devices get more compact, transistors must handle the electrical current in smaller and smaller areas. 

PHOTO CREDIT: University of Utah

The ultrafast laser shoots very short light pulses 80 million times a second at the hybrid perovskite material to determine whether its electrons could be used to carry information in future devices. They split the laser into two beams; the first one hits the film to set the electron spin in the desired direction. The second beam bends through a series of mirrors like a pin ball machine before hitting the perovskite film at increasing time intervals to measure how long the electron held the spin in the prepared direction.

“The silicon technology, based only on the electron charge, is reaching its size-limit,” says Li, “The size of the wire is already small. If gets any smaller, it’s not going to work in a classical way that you think of.” 

“People were thinking, ‘How do we increase the amount of information in such a small area?’” adds Vardeny. “What do we do to overcome this limit?” 

“Spintronics,” answers physics. 

Spintronics uses the spin of the electron itself to carry information. Electrons are basically tiny magnets orbiting the nucleus of an element. Just like the Earth has its own orientation relative to the sun, electrons have their own spin orientation relative to the nucleus that can be aligned in two directions: “Up,” which represents a one, and “down,” which represents a zero. Physicists relate the electron’s “magnetic moment” to its spin. 

By adding spin to traditional electronics, you can process exponentially more information than using them classically based on less or more charge. 

“With spintronics, not only have you enormously more information, but you’re not limited by the size of the transistor. The limit in size will be the size of the magnetic moment that you can detect, which is much smaller than the size of the transistor nowadays,” says Vardeny. 

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