Scientists develop world’s thinnest magnet

According to the researchers, the magnet could make advances in next-gen memories, computing, spintronics – such as high-density, compact spintronic memory devices – and quantum physics. It was developed by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.

“We’re the first to make a room-temperature 2D magnet that is chemically stable under ambient conditions,” said senior author Jie Yao, a faculty scientist in Berkeley Lab’s Materials Sciences Division and associate professor of materials science and engineering at UC Berkeley.

Graduate student at UC Berkeley, Rui Chen, added: “This discovery is exciting because it not only makes 2D magnetism possible at room temperature, but it also uncovers a new mechanism to realise 2D magnetic materials.”

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

Previous achievements in 2D magnetic materials have brought promising results. But these early 2D magnets lose their magnetism and become chemically unstable at room temperature, according to experts.

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

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

The researchers synthesised the new 2D magnet – called a cobalt-doped van der Waals zinc-oxide magnet – from a solution of graphene oxide, zinc, and cobalt. Just a few hours of baking in a conventional lab oven transformed the mixture into a single atomic layer of zinc oxide with a smattering of cobalt atoms sandwiched between layers of graphene. In a final step, graphene is burned away, leaving behind just a single atomic layer of cobalt-doped zinc oxide.

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

With proof in hand that their 2D material really is just an atom thick, the researchers went on to the next challenge that had confounded researchers for years: demonstrating a 2D magnet that successfully operates at room temperature.

The research team’s lab experiments showed that the graphene-zinc-oxide system becomes weakly magnetic with a 5-6 per cent concentration of cobalt atoms. Increasing the concentration of cobalt atoms to about 12 per cent results in a powerful magnet.

They also found that a concentration of cobalt atoms exceeding 15 per cent shifts the 2D magnet into an exotic quantum state of “frustration,” whereby different magnetic states within the 2D system compete with each other. And unlike previous 2D magnets, which lose their magnetism at room temperature or above, the researchers found that the new 2D magnet not only works at room temperature but also at 100°C.

According to Chen, zinc oxide’s free electrons could act as an intermediary that ensures the magnetic cobalt atoms in the new 2D device continue pointing in the same direction – and thus stay 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.

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