In a groundbreaking experiment over a century ago, physicists Albert Einstein and Wander de Haas discovered that by exposing an iron cylinder to a reversed magnetic field, it would start rotating without any physical contact. This phenomenon, known as the Einstein-de Haas effect, has fascinated scientists and has now been extended to a new class of materials called “anti”-ferromagnets. Researchers from the U.S. Department of Energy’s Argonne National Laboratory and other institutions have revealed a similar yet distinct effect in antiferromagnets, which could have significant implications for ultra-precise and ultrafast motion control in various technological applications.
The Distinction Between Ferromagnets and Antiferromagnets
The fundamental difference between ferromagnets and antiferromagnets lies in the electron spin, a property associated with the direction of the spin of electrons. In ferromagnets, all of the electrons within the material align in the same direction, resulting in a strong response to changes in a magnetic field. When the magnetic field is reversed, the alignment of the electron spins also reverses, causing the rotation of a suspended iron cylinder, as observed in the Einstein-de Haas experiment. On the other hand, in antiferromagnets, the spins of adjacent electrons alternate between up and down, effectively canceling each other out and preventing a response to magnetic field changes.
The Quest to Elicit a Mechanical Response in Antiferromagnets
Motivated by the desire to understand whether an analogous response could be elicited in antiferromagnets, the team of researchers focused on iron phosphorus trisulfide (FePS3), an antiferromagnetic material with a unique layered structure. By subjecting FePS3 to ultrafast laser pulses, the team found that the ordered orientation of electron spins became disordered, leading to a mechanical response throughout the material. Due to the weak interaction between the layers in FePS3, one layer was able to slide back and forth with respect to an adjacent layer, resulting in ultrafast motion with oscillation periods as short as 10 to 100 picoseconds.
Unveiling the Mechanism
To unravel the interplay between electron spin and atomic motion, the team utilized cutting-edge scientific facilities capable of atomic-scale and picosecond-resolved measurements. The mega-electronvolt ultrafast electron diffraction facility at SLAC National Accelerator Laboratory and the ultrafast electron diffraction setup at MIT provided key insights into the atomic structure and dynamics. Additionally, the ultrafast electron microscope facility in the Center for Nanoscale Materials and the 11-BM and 7-ID beamlines at the Advanced Photon Source enabled comprehensive analyses of FePS3.
Implications for Nanoscale Devices
The significance of this research extends beyond fundamental scientific understanding. By harnessing the relationship between electron spin and atomic motion in layered antiferromagnets, it becomes possible to control this ultrafast motion through manipulation of the magnetic field or application of minute strains. This breakthrough has immense potential for the development of nanoscale devices, such as high-speed nanomotors for biomedical applications. Nanorobots capable of minimally invasive diagnosis and surgery could benefit from this newfound ability to achieve ultra-precise and ultrafast motion control.
The study conducted by scientists from Argonne National Laboratory and other institutions sheds light on the remarkable connection between electron spin and motion in antiferromagnets. By uncovering the ability to induce ultrafast motion through disordering the electron spin orientation, researchers have paved the way for future advancements in nanoscale motion control. The implications for biomedical applications, particularly with nanorobotics, are promising. The ability to manipulate these materials through magnetic fields or strains opens up a world of possibilities for the development of novel nanoscale devices that could revolutionize the field of medicine.
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