Scientists create the world’s thinnest magnet

The development of an ultrathin magnet operating at room temperature could lead to new applications in computer science and electronics, such as compact high density spintronic memories, and new tools for the study of quantum physics.

The ultrathin magnet, which was recently reported in the newspaper Nature Communication , could make great progress in next-generation memories, computing, spintronics and quantum physics. It was discovered by scientists at the Lawrence Berkeley National Laboratory (Berkeley Lab) of the Department of Energy and UC Berkeley.

“We are the first to manufacture a 2-D room-temperature magnet that is chemically stable under room conditions,” said lead author Jie Yao, a researcher in the Materials Sciences division of the Berkeley Lab and associate professor of science and Materials Engineering at UC Berkeley.

“This discovery is exciting because it not only makes 2D magnetism possible at room temperature, but it also uncovers a new mechanism for making 2D magnetic materials,” added Rui Chen, UC Berkeley graduate student in the group of Yao research and author director of the study. “

The magnetic component of today’s memory devices is usually made of magnetic thin films. But at the atomic level, these magnetic films are always three-dimensional – hundreds or thousands of atoms thick. For decades, researchers have searched for ways to make thinner, smaller 2D magnets and thus allow data to be stored at a much higher density.

Previous achievements in the field of 2-D magnetic materials have brought promising results. But these early 2-D magnets lose their magnetism and become chemically unstable at room temperature.

“State-of-the-art 2-D magnets need very low temperatures to operate. But for practical reasons, a data center must operate at room temperature,” Yao said. “Theoretically, we know that the smaller the magnet, the greater the potential data density of the drive. Our 2-D magnet is not only the first one that operates at room temperature or higher, but it is also the first magnet to reach true 2-D. Limit D: It’s as thin as a single atom! “

The researchers say their discovery will also open up new opportunities to study quantum physics. “Our atomically thin magnet provides an optimal platform for probing the quantum world,” Yao said. “This opens up each atom for examination, which can reveal how quantum physics governs each magnetic atom and the interactions between them. With a conventional bulk magnet where most of the magnetic atoms are buried deep inside the material, such studies would be quite difficult to do. “

The making of a 2-D magnet that can take heat

The researchers synthesized the new 2-D magnet, called the cobalt-doped zinc oxide van der Waals magnet, from a solution of graphene oxide, zinc and cobalt. A few hours of baking in a conventional laboratory oven turned the mixture into a single atomic layer of zinc oxide with a handful of cobalt atoms sandwiched between layers of graphene. In a final step, the graphene is burnt, leaving only a single atomic layer of zinc oxide doped with cobalt.

“With our equipment, there are no major obstacles for the industry to adopt our solution-based method,” said Yao. “It’s potentially scalable for mass production at lower cost. “

To confirm that the resulting 2D film was only one atom thick, Yao and his team conducted scanning electron microscopy experiments at the Berkeley Lab Molecular Foundry to identify the material’s morphology and electron microscopy imaging. transmission to probe the material atom by atom.

With proof in hand that their 2D material is actually only an atom thick, the researchers embarked on the next challenge that had baffled them for years: demonstrating a 2D magnet that works successfully at room temperature. .

X-ray experiments at the advanced light source from Berkeley Lab characterized the magnetic parameters of the 2D material at high temperature. Additional x-ray experiments at the Stanford synchrotron radiation light source of the National Accelerator Laboratory at SLAC verified the electronic and crystal structures of the synthesized 2D magnets. And at the Nanoscale Materials Center of the Argonne National Laboratory, researchers imaged the crystal structure and chemical composition of the material in 2D using transmission electron microscopy.

Overall, the research team’s laboratory experiments have shown that the graphene-zinc oxide system becomes weakly magnetic with a concentration of 5-6 atomic percent cobalt. Increasing the concentration of cobalt atoms to about 12% results in a very strong magnet.

To the researchers’ surprise, a concentration of cobalt atoms exceeding 15% shifts the 2D magnet into an exotic quantum state of “frustration”, in which different magnetic states of the 2D system compete with each other.

And unlike previous 2-D magnets, which lose their magnetism at room temperature or above, the researchers found that the new 2-D magnet operates not only at room temperature but also at 100 degrees Celsius (212 degrees Fahrenheit).

“Our 2D magnetic system shows a distinct mechanism compared to previous 2D magnets,” Chen said. “And we believe this unique mechanism is due to the free electrons in zinc oxide.”

True north: free electrons keep magnetic atoms on track

When you command your computer to save a file, this information is stored as a series of ones and zeros in the computer’s magnetic memory, such as the magnetic hard drive or flash memory. And like all magnets, magnetic memories contain microscopic magnets with two poles, north and south, whose orientations follow the direction of an external magnetic field. Data is written or encoded when these tiny magnets are flipped in the desired directions.

According to Chen, the free electrons in the zinc oxide could serve as an intermediary ensuring that the magnetic cobalt atoms in the new 2-D device continue to point in the same direction – and thus remain magnetic – even when the host, in this case the semiconductor zinc oxide is a non-magnetic material.

“Free electrons are constituents of electric currents. They move in the same direction to conduct electricity,” Yao added, comparing the movement of free electrons in metals and semiconductors to the flow of water molecules. in a stream of water.

Researchers say a new material, which can be bent into almost any shape without breaking, and is a millionth the thickness of a single sheet of paper, could help advance the application spin electronics or spin electronics, a new technology that uses the orientation of an electron’s spin rather than its charge to encode data. “Our 2-D magnet can enable the formation of ultra-compact spintronic devices to design the spins of electrons,” Chen said.

“I think the discovery of this new, robust and truly two-dimensional magnet at room temperature is a real breakthrough for Jie Yao and his students,” said co-author Robert Birgeneau, senior researcher in the Materials Sciences Division of the Berkeley Lab and professor of physics at UC Berkeley who co-directed the magnetic measurements of the study. “In addition to its obvious importance to spintronic devices, this 2D magnet is fascinating at the atomic level, revealing for the first time how magnetic cobalt atoms interact over” long “distances” through a complex two-dimensional lattice. -he adds.

“Our results are even better than we expected, which is really exciting. Most of the time in science, the experiments can be very difficult,” he said. “But when you finally do something new, it’s always very rewarding.”