Using Perovskite in Spintronic Devices

Mobile phones, computers and other electronic devices use silicon transistors to control the flow of electrical current, but as devices get smaller these transistors are expected to function in smaller areas, to the point that they will no longer work as expected.

Spintronics, however, could solve the problem. It uses the spin of an electron itself to carry information in binary; electrons have their own spin orientation relative to the nucleus that can be aligned in two directions, up or down. This means they are capable of carrying information in larger quantities than current devices.

But making spintronic devices is difficult, explains Sarah Li, assistant professor in the Department of Physics and Astronomy at the University of Utah: "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."

Li and her team have discovered that organic-inorganic hybrid perovskites may be capable of advancing electronics to the next level. Perovskites have already found scientific fame 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 and Astronomy, whose lab studies perovskite solar cells. "In just a few years, solar cells based on this material are at 22% efficiency. And now it has this spin lifetime property. It's fantastic."

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Perovskite is an unlikely candidate for spintronics; its chemical composition includes a heavy element inorganic frame. While the heavy atom allows for easier manipulation of the electron spin, it was presumed it would have a short spin lifetime.

"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."

Adding spin to traditional electronics means that you can process exponentially more information than using them classically, based on more or less charge. Vardeny explains: “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.”

Li’s team conducted an experiment to tune the spin of the electron. First, they formed a thin film from the hybrid perovskite methyl-ammonium lead iodine (CH₃NH₃PbI₃) and placed it in front of an ultrafast laser that shoots very short light pulses 80 million times a second, making them the first to use light to set the electron's spin orientation and observe the spin precession in this material.

Next, the laser was split into two beams; the first one hit the film to set the electron spin in the desired direction. The second beam bends through a series of mirrors before striking the perovskite film at increasing time intervals to measure how long the electron held the spin in the prepared direction.

The perovskite has a surprisingly long spin lifetime - up to nanosecond, the researchers found. The spin flipped many times during one nanosecond, which means lots of information can be easily stored and manipulated during that time. Next, the researchers tested how well they could manipulate the spin with a magnetic field.

"The spin is like the compass. The compass spins in this magnetic field perpendicular to that compass, and eventually it will stop spinning," says Li. "Say you set the spin to 'up,' and you call that 'one': when you expose it to the magnetic field, the spin changes direction. If it rotated 180 degrees, it changes from one to zero. If it rotated 360 degrees, it goes from one to one."

The researchers found that they could rotate the spin more than 10 turns by exposing the electron to different strengths of magnetic field.

The potential for this material is enormous, says Vardeny. It could process data faster and increase random-access memory: “I'm telling you, it's a miracle material".

Source:

University of Utah

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