Did you know that a simple paper clip can stick to a magnet? It’s because paper clips are made of iron, which is classified as a ferromagnet. But here’s something even more fascinating: over a century ago, physicists Albert Einstein and Wander de Haas discovered that if you suspend an iron cylinder from a wire and expose it to a magnetic field, it will start rotating just by reversing the direction of the magnetic field. It’s like magic!
“Einstein and de Haas’s experiment is almost like a magic show,” said Haidan Wen, a physicist at the U.S. Department of Energy’s Argonne National Laboratory. “You can cause a cylinder to rotate without ever touching it.”
Now, in a recent study published in Nature, a team of researchers from Argonne and other national laboratories and universities have found a similar effect in an “anti”-ferromagnet. This discovery could have significant applications in devices that require ultra-precise and ultrafast motion control, such as high-speed nanomotors for biomedical purposes.
The difference between a ferromagnet and an antiferromagnet lies in a property called electron spin. In a ferromagnet, all the electron spins point in the same direction, but in an antiferromagnet, the spins alternate between up and down. This difference in spin behavior is what allows the iron cylinder to rotate in the Einstein-de Haas experiment.
To explore whether electron spin can elicit a similar response in an antiferromagnet, the team conducted experiments using a layered antiferromagnet called iron phosphorus trisulfide (FePS3). They discovered that by scrambling the ordered orientation of electron spins with ultrafast laser pulses, they could induce a mechanical response in the material. This response resulted in the sliding motion of layers within the sample, occurring at an astonishing speed of 10 to 100 picoseconds per oscillation.
These groundbreaking findings were made possible through the use of cutting-edge scientific facilities, including ultrafast electron and X-ray beams for atomic structure analysis. The team’s research spanned multiple institutions, such as the University of Washington, SLAC National Accelerator Laboratory, MIT, and Argonne’s Center for Nanoscale Materials and Advanced Photon Source.
By uncovering the link between electron spin and atomic motion in layered antiferromagnets, the researchers believe that this discovery could have significant implications for nanoscale devices. The ability to control motion by changing the magnetic field or applying a tiny strain opens up new possibilities for advanced technology.
