Breakthrough Atomically Thin Magnets Offer Researchers Surprising Power
A team from Cornell University has successfully manipulated atomically thin magnets with an electric field, giving hope to greatly improved data storage for computer chips and other electronics.
Jie Shan, a professor of applied and engineering physics, worked alongside his colleague and assistant professor of physics Kin Fai Mak on the study. Postdoctoral student Shengwei Jiang also collaborated on the study.
They based their developments off of the 1966 work of Cornell physicist David Mermin and his postdoc Herbert Wagner. Wagner and Mermin theorized that 2D magnets couldn't exist if the spins of their electrons could point in any direction. However, it took until 2017 that some 2D materials showed promise of having the proper alignment of spins. This led to a new family of materials -- 2D van der Waals magnets.
Shan and Mak both specialized in atomically thin materials. They decided to pursue researching these new magnets and explore the potential that their unique characteristics could offer the technology.
"If it's a bulk material, you can't easily access the atoms inside," said Mak. "But if the magnet is just a monolayer, you can do a lot to it. You can apply an electric field to it, put extra electrons into it, and that can modulate the material properties."
The researchers used chromium triiodide to see just how much they could affect the material properties. The applied a small amount of voltage to form an electric field and control the 2D compound's magnetism. This allowed them to turn on and off the magnetism.
They stacked the two atomic layers of chromium triiodide with thin gate dielectrics and electrodes. According to the study, this became a field-effect device that could change the electron-spin direction in the chromium triiodide layers using small gate voltages. The team noted that the process is both reversible and repeatable under 57-degrees Kelvin (-357 Fahrenheit or -216 Celsius).
The discovery could have widespread implications on existing technology already based on magnetic switching, Shan said. Currently, magnets found in modern electronics don't respond to an electric field, but rather by passing current through a coil. That creates the magnetic field that can then switch a magnet on and off. The Cornell team pointed out the inefficiencies of the process; the current both creates heat and consumes electricity.
The 2D chromium-triiodide magnets, on the other hand, can have an electric field directly applied to them to activate switching with very little energy being consumed.
"The process is also very effective because if you have a nanometer thickness and you apply just one volt, the field is already 1 volt per nanometer. That’s huge," Shan said.
The team will continue to test the capabilities of 2D magnets. They also want to use their research to build relationships with other engineering departments around campus and off-campus. They hope their partnerships with more scientists and engineers could help them develop new 2D materials that can work at room temperature rather than chromium triiodide's sub-zero temps.
“In a sense, what we have demonstrated here is more like a device concept,” said Mak. “When we find the right kind of material that can operate at a higher temperature, we can immediately apply this idea to those materials. But it’s not there yet.”