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A slice of material just one atom thick breaks records.
The ultra-thin wafer is a magnet that operates at room temperature, opening avenues for the development of technology, especially memory devices, and for research in ferromagnetism and quantum physics.
This is a huge step forward from previous attempts to fabricate a 2D magnet, which lost their magnetism and stability when removed from ultra-cold conditions.
“We are the first to manufacture a 2D magnet at room temperature that is chemically stable under room conditions,” said materials scientist Jie Yao of the University of California at Berkeley.
“State-of-the-art 2D magnets need very low temperatures to function. But for practical reasons, a data center should operate at room temperature. Our 2D magnet is not only the first to operate at room temperature or higher, but it’s also the first magnet to reach the true 2D limit – it’s as thin as a single atom! “
This amazing achievement was made using a material called van der Waals zinc oxide doped with cobalt. As the name suggests, it is created by combining graphene oxide, zinc and cobalt. Graphene oxide is immersed in zinc acetate and cobalt dihydrates, the ratios of which are carefully measured.
When cooked under vacuum, this mixture slowly cools down into a single layer of zinc oxide studded with cobalt atoms, sandwiched between layers of graphene. An air firing step burns the graphene, leaving the single layer of cobalt-doped zinc oxide.
The team then used scanning electron microscopy to confirm the thickness of a single atom in the structure and transmission electron microscopy to image the crystal structure and composition, atom by atom.
Illustration of the magnetic coupling in the material. (Berkeley Laboratory)
The resulting 2D film was found to be magnetic, but the exact degree of magnetism depended on the amount of cobalt dispersed among the zinc oxide. At about 5 to 6 percent, the magnetism was quite weak. Doubled to about 12 percent, the material became quite strongly magnetic.
At 15%, the material was so strongly magnetic that localized spins in the material began to compete with each other, a condition known as frustration. This can hamper the magnetic order within a system, so it seems like around 12% is the sweet spot for cobalt.
Interestingly, the film remained magnetic and chemically stable not only at room temperature, but up to temperatures of around 100 degrees Celsius (212 degrees Fahrenheit) – even though zinc oxide is not a ferromagnetic material.
“Our 2D magnetic system shows a distinct mechanism compared to previous 2D magnets,” said Rui Chen of UC Berkeley, materials scientist and first author of the study. “And we believe this unique mechanism is due to the free electrons in zinc oxide.”
Electrons are, among others, very small magnets. Each electron has a north and south magnetic pole and its own small magnetic field. In most materials, the magnetic orientations of electrons cancel out, but in ferromagnetic materials, electrons cluster together in areas where they all have the same magnetic orientation. In a magnetic material, all the domains are oriented in the same direction.
Free electrons are those that are not attached to the nucleus of an atom. The researchers believe that the free electrons in zinc oxide could act as intermediaries that keep the magnetic cobalt atoms in the film oriented in the same direction, even at high temperatures.
This is certainly something that deserves further investigation, especially since it could open so many new avenues for the development of technology and research. The film itself is flexible and its manufacturing scalable, which means the possibilities are dazzling.
One avenue is the study of magnetic interactions between atoms, which has implications for quantum physics. Another is spintronics, the study of the spin of electrons. It could also be used to fabricate lightweight and flexible memory devices, which rely on switching the orientation of the magnetic field to encode binary data.
Future analyzes and calculations will provide a better understanding of the material’s limitations.
“Our results are even better than we expected, which is really exciting. Most of the time in science, the experiments can be very difficult,” Yao said. “But when you finally do something new, it’s always very rewarding.”
The research was published in Nature Communication.
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