Addressing Fundamental Limits of Ultrafast Devices at the University of Illinois
Researchers at the University of Illinois at Urbana-Champaign and the Korean Institute of Science and Technology (KIST) have uncovered physical mechanisms that enable laser light to alter the magnetization of a metal.
"In our study, we illuminate thin layers of the cobalt, iron or nickel with pulses of laser light that have a duration of a trillionth of a second. A small fraction of the angular momentum of the photons in the laser pulse is transferred to the metal layer and causes the magnet to oscillate, in a manner analogous to the precession of a spinning top," said David Cahill, a Donald B. Willett Professor of Engineering and head of the Department of Materials Science and Engineering at Illinois. "The physics of manipulating a magnetic material with light is closely related to how a magnetic material changes the polarization of light. The effect is named after the famous 19th century English scientist Michael Faraday and has important applications in fiber optic communication systems."
“The significance of our work is that we have measured, for the first time, the inverse of the Faraday effect in metallic ferromagnets,” explained Gyung-Min Choi, who recently completed his PhD degree in materials science and engineering at Illinois. Choi now works at KIST. “Typically, magnetic fields are used to manipulate magnetic information. Our work shows how light with circularly polarization has an effect on a magnet that is similar to a magnetic field.”
Choi is lead author of the paper, “Optical-helicity-driven magnetization dynamics in metallic ferromagnets,” recently published in Nature Communications. “When the magnetic layer is coated with a few nanometers of platinum, the inverse Faraday effect is enhanced,” Choi added. “This result shows that the angular momentum of light can be converted more effectively in a heavy metal such as platinum than in the magnetic layer itself. Professor Schleife’s calculations help explain why this happens.”
Cahill’s research group at Illinois studies the physical mechanisms governing the interplay of charge, light, spin and heat at the nanoscale, addressing the fundamental limits of ultrafast devices for data storage and information processing. In addition to Choi and Cahill—whose work was supported by the Army Research Office MURI program—the paper is co-authored by materials science and engineering assistant professor Andre Schleife at the University of Illinois, who specializes in atomistic, quantum-mechanical modeling of interactions between light and materials.