On the generality of the LLG equation to the optical limit: An optically-induced helicity dependent torque emerging from the LLG equation

Benjamin Assouline, Amir Capua*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

It is well known that the Gilbert relaxation time of a magnetic moment scales inversely with the magnitude of the externally applied field, H, and the Gilbert damping, α. Therefore, in ultrashort optical pulses, where H can temporarily be large, the Gilbert relaxation time can momentarily be extremely short, reaching even picosecond timescales. Here we show that for typical ultrashort pulses, the magnetization can respond within the optical cycle such that the optical control of the magnetization emerges by merely considering the optical magnetic field in the Landau-Lifshitz-Gilbert (LLG) equation. Interestingly, when circularly polarized optical pulses are introduced to the LLG equation, an optically induced helicity-dependent torque results. We find that the strength of the interaction is determined by N = ayH/F"#, where fc!"# and yare the optical frequency and gyromagnetic ratio. Our results illustrate the generality of the LLG equation to the optical limit and the pivotal role of the Gilbert damping in the general interaction between optical magnetic fields and spins in solids.

Original languageAmerican English
Title of host publicationSpintronics XVI
EditorsJean-Eric Wegrowe, Joseph S. Friedman, Manijeh Razeghi
PublisherSPIE
ISBN (Electronic)9781510665262
DOIs
StatePublished - 2023
EventSpintronics XVI 2023 - San Diego, United States
Duration: 20 Aug 202324 Aug 2023

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume12656
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceSpintronics XVI 2023
Country/TerritoryUnited States
CitySan Diego
Period20/08/2324/08/23

Bibliographical note

Publisher Copyright:
© 2023 SPIE.

Keywords

  • Landau-Lifshitz-Gilbert equation
  • all-optical magnetization switching
  • helicity dependent magnetization switching
  • magneto-optics
  • ultrafast magnetization dynamics

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