Van der Waals materials Magnetic 2D materials for energy-efficient CPUs

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An MIT team has achieved precise control of an ultra-thin magnet at room temperature, potentially paving the way for faster and more efficient processors and memory systems.

Experimental computer memory and processors made of magnetic materials consume far less energy than traditional silicon-based devices. Two-dimensional magnetic materials, consisting of layers just a few atoms thick, have incredible properties that could potentially enable unprecedented speed, efficiency, and scalability with magnetic components.

Although many hurdles still need to be overcome before these so-called Van der Waals magnetic materials can be integrated into working computers, MIT researchers have taken an important step in this direction by demonstrating the precise control of a Van der Waals magnet at room temperature.

This is crucial because magnets made from atomically thin Van der Waals materials can usually only be controlled at extremely low temperatures, which makes their use outside of a laboratory difficult.

Current pulses to control magnetization

The researchers used electrical current pulses to change the direction of the component's magnetization at room temperature. Magnetic switching can be used for calculations, just like a transistor switches between open and closed to represent 0 and 1 in binary code. Or in computer memory, where the switching allows data storage.

The team fired electron bursts at a magnet made of a new material that can maintain its magnetism even at higher temperatures. The experiment utilized a fundamental property of electrons, the so-called spin, which makes the electrons behave like tiny magnets. By manipulating the spin of the electrons hitting the component, the researchers can switch its magnetization.

"The heterostructure device we developed requires an order of magnitude less electrical current to switch the van der Waals magnet than is the case with magnetic components," says Deblina Sarkar, professor at the MIT Media Lab and Center for Neurobiological Engineering, head of the "Nano-Cybernetic Biotrek" group and lead author of a report on this technique. "Our device is also more energy-efficient than other van der Waals magnets that cannot switch at room temperature."

In the future, such a magnet could be used to build faster computers that consume less power. It could also enable non-volatile magnetic computer memory, which means they don't lose information when turned off - or processors that run complex AI algorithms more energy-efficiently.

"There's a lot of inertia in trying to improve materials that have worked smoothly in the past. However, we have shown that through radical changes, starting with rethinking the materials used, you can potentially achieve many better solutions," said Shivam Kajale, a doctoral student in Sarkar's lab and co-author of the study.

An atomically thin advantage

The methods of making tiny computer chips in a clean room from bulk materials like silicon can impair the components. For example, the material layers can hardly be 1 nm thick, because then tiny rough spots on the surface would likely severely impair the performance.

In contrast, magnetic van der Waals materials are naturally layered and structured in such a way that the surface remains perfectly smooth, even when scientists peel off layers to make thinner components. In addition, the atoms of one layer do not penetrate into other layers, allowing the materials to retain their unique properties when stacked in components.

"When it comes to scaling these magnetic devices and making them competitive for commercial applications, van der Waals materials are the way to go," said Kajale. However, there is a catch. This new class of magnetic materials has so far only been used at temperatures below 60 Kelvin. In order to build a magnetic computer processor or memory, the researchers must operate the magnet at room temperature with electric current.

To achieve this, the team focused on a new material called iron gallium telluride. This atomically thin material has all the properties required for effective magnetism at room temperature. And it does not contain any rare earths, which are undesirable because their extraction is particularly damaging to the environment.

Nguyen grew bulk crystals of this 2D material using a special technique. Then, Kajale created a dual-layer magnetic component that contains nano-flakes of iron gallium telluride beneath a 6 nm thick layer of platinum. In the tiny component, they used an intrinsic property of electrons, the so-called spin, to change the magnetization at room temperature.

Electron ping pong

Although electrons technically do not "spin" like a top, they possess the same kind of angular momentum. This spin has a direction, either upwards or downwards. The researchers can take advantage of a property known as spin-orbit coupling to control the spins of the electrons they shoot at the magnet.

Just as momentum is transferred when one ball hits another, the electrons transfer their "spin momentum" to the 2D magnetic material when they hit it. Depending on the direction of their spins, this momentum transfer can reverse the magnetization.

In a sense, this transfer rotates the magnetization from top to bottom (or vice versa), which is why it is also referred to as "torque" as in spin-orbit torque switching. A negative electrical pulse causes the magnetization to go down, a positive pulse causes it to go up.

The researchers can perform this switching at room temperature for two reasons, due to the special properties of iron gallium telluride and the fact that their technique only requires small amounts of electric current. If too much current were pumped into the device, it would overheat and demagnetize.

The team faced many challenges in the two years it took to reach this milestone, Kajale said. Finding the right magnetic material was only half the battle. Since iron gallium telluride oxidizes quickly, the manufacturing must take place in a nitrogen-filled glove box. "The component is only exposed to air for 10 or 15 seconds, but even then I have to polish it to remove any oxide," he explained.

Having now demonstrated switching at room temperature and higher energy efficiency, the researchers want to further boost the performance of magnetic van der Waals materials. "Our next milestone is to achieve switching without external magnetic fields. Our goal is to improve and scale up our technology to harness the versatility of van der Waals magnets for commercial applications," said Sarkar. This research was partially carried out using the facilities of MIT.nano and the Harvard University Center for Nanoscale Systems. (sb)

Link: Massachusetts Institute of Technology