MIT News: Scientists Utilize 2D Magnetic Materials for Eco-Friendly Computing

Exploratory computer memories and processors created from magnetic materials consume much less energy than traditional silicon-based devices. Magnetic materials composed of two-dimensional layers that are only a few atoms thick possess remarkable characteristics that could enable magnetic-based devices to achieve unparalleled speed, efficiency, and scalability.

Even though there are numerous obstacles to overcome before these so-called van der Waals magnetic materials can be integrated into operational computers, MIT researchers have taken a significant step in this direction by demonstrating precise control of a van der Waals magnet at room temperature.

This is crucial, as magnets made of atomically thin van der Waals materials can generally only be manipulated at extremely cold temperatures, making it difficult to utilize them outside a laboratory.

Using pulses of electrical current, the researchers were able to alter the orientation of the device’s magnetization at room temperature. Magnetic switching can be utilized in computation, in the same way a transistor shifts between open and closed to represent 0s and 1s in binary code, or in computer memory, where switching allows for data storage.

The team directed bursts of electrons at a magnet composed of a new material that can maintain its magnetism at higher temperatures. The experiment utilized a fundamental property of electrons called spin, which causes the electrons to act like tiny magnets. By manipulating the spin of electrons that collide with the device, the researchers can alter its magnetization.

“The heterostructure device we have created demands ten times less electrical current to switch the van der Waals magnet, compared to that necessary for bulk magnetic devices,” says Deblina Sarkar, the AT&T Career Development Assistant Professor in the MIT Media Lab and Center for Neurobiological Engineering, head of the Nano-Cybernetic Biotrek Lab, and the senior author of a paper on this method. “Our device is also more energy efficient than other van der Waals magnets that are unable to switch at room temperature.”

In the future, such a magnet could be utilized to construct faster computers that consume less electricity. It could also enable nonvolatile magnetic computer memories, which means they don’t leak information when powered off, or processors that make complex AI algorithms more energy-efficient.

“There is a lot of inertia around trying to improve materials that worked well in the past. But we have shown that if you make radical changes, starting by rethinking the materials you are using, you can potentially get much better solutions,” says Shivam Kajale, a graduate student in Sarkar’s lab and co-lead author of the paper.

Kajale and Sarkar are joined on the paper by co-lead author Thanh Nguyen, a graduate student in the Department of Nuclear Science and Engineering (NSE); Corson Chao, a graduate student in the Department of Materials Science and Engineering (DSME); David Bono, a DSME research scientist; Artittaya Boonkird, an NSE graduate student; and Mingda Li, associate professor of nuclear science and engineering. The research appears this week in Nature Communications.

A razor-thin advantage

Approaches to manufacture tiny computer chips in a clean room from bulk materials like silicon can impede devices. For example, the layers of material may be scarcely 1 nanometer thick, so tiny bumps on the surface can be severe enough to degrade performance.

By contrast, van der Waals magnetic materials are inherently layered and structured in a way that the surface remains perfectly smooth, even as researchers peel off layers to create thinner devices. Furthermore, atoms in one layer won’t seep into other layers, allowing the materials to retain their unique properties when stacked in devices.

“In terms of scaling and making these magnetic devices competitive for commercial applications, van der Waals materials are the way to go,” Kajale says.

But there’s a drawback. This new class of magnetic materials have typically only been operated at temperatures below 60 kelvins (-351 degrees Fahrenheit). To construct a magnetic computer processor or memory, researchers need to use electrical current to operate the magnet at room temperature.

To achieve this, the team focused on an emerging material called iron gallium telluride. This atomically thin material has all the properties needed for effective room temperature magnetism and doesn’t contain rare earth elements, which are undesirable because extracting them is especially destructive to the environment.

Nguyen meticulously grew bulk crystals of this 2D material using a specialized technique. Then, Kajale fabricated a two-layer magnetic device using nanoscale flakes of iron gallium telluride underneath a six-nanometer layer of platinum.

With a tiny device in hand, they used an intrinsic property of electrons known as spin to alter its magnetization at room temperature.

Electron ping-pong

While electrons don’t technically “spin” like a top, they do possess the same kind of angular momentum. That spin has a direction, either up or down. The researchers can leverage a property known as spin-orbit coupling to control the spins of electrons they fire at the magnet.

The same way momentum is transferred when one ball hits another, electrons will transfer their “spin momentum” to the 2D magnetic material when they strike it. Depending on the direction of their spins, that momentum transfer can reverse the magnetization.

In a sense, this transfer rotates the magnetization from up to down (or vice-versa), so it is called a “torque,” as in spin-orbit torque switching. Applying a negative electric pulse causes the magnetization to go downward, while a positive pulse causes it to go upward.

The researchers can do this switching at room temperature for two reasons: the special properties of iron gallium telluride and the fact that their technique uses small amounts of electrical current. Pumping too much current into the device would cause it to overheat and demagnetize.

The team encountered numerous challenges over the two years it took to achieve this milestone, Kajale says. Finding the right magnetic material was only half the battle. Since iron gallium telluride oxidizes quickly, fabrication must be done inside a glovebox filled with nitrogen.

“The device is only exposed to air for 10 or 15 seconds, but even after that I have to do a step where I polish it to remove any oxide,” he says.

Now that they have demonstrated room-temperature switching and greater energy efficiency, the researchers plan to keep pushing the performance of magnetic van der Waals materials.

“Our next milestone is to achieve switching without the need for any external magnetic fields. Our aim is to enhance our technology and scale up to bring the versatility of van der Waals magnet to commercial applications,” Sarkar says.

This work was carried out, in part, using the facilities at MIT.Nano and the Harvard University Center for Nanoscale Systems.

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