All Optical Switching (AOS)

It has been known for some time that magnetic moment of a certain ferrimagnetic alloys can be completely reversed using ultrafast pulses of circularly polarized light in the absence of an external magnetic field. Although this effect has been first observed in relatively complex ferrimagnetic alloys, a more recent discovery shows that also ferromagnetic superlattices can be switched by light. This extremely interesting discovery opens the door to applications in novel magnetic memories and spintronics applications.

All Optical Switching (AOS)
Figure: (a) Schematics of all-optical switching (AOS) and the domain imaging setup. (b) Dark (bright) lines on bright (dark) background and grey areas show domain formation or demagnetization due to the exposure to right (σ+), left (σ+) and linearly (π) polarized light, respectively. Dark and white areas correspond to two opposite out-of-plane magnetization directions. (b) The overall area of the magnetically affected spot as well the area of the fully-switched region at the perimeter of the spot, scale with the laser fluence and the number of pulses.

In our AOS project, we grow ferromagnetic [Co/Pt]N superlattices on top of silicon and glass substrates and investigate magnetization switching as a function material composition, thickness, number of layers, as well as laser beam properties. We employ a femtosecond laser amplifier and a quarter wave plate in order to vary the light polarization. We then analyze the impact of the laser light on a superlattice using either Kerr or Faraday imaging or magnetic force microscopy. An example of the optically switched [Co/Pt]N superlattice is shown in the figure below.

Kerr microscopy images show that laser-illuminated areas exhibit domain formation at the centre and complete magnetization reversal via AOS at the perimeter of the illuminated regions. Illuminated lines are broader at high laser fluence due to the broadened Gaussian intensity profile. If the laser beam is not scanned but stays at one spot (that receives a larger number of laser shots), the magnetically affected area also shows broadening that is proportional to the number of pulses. The latter is ascribed to the radial heat propagation around the illuminated spot.

Publications

T. Ohkochi, R. Takahashi, H. Fujiwara, H. Takahashi, R. Adam, U. Parlak, K. Yamamoto, H. Osawa, M. Kotsugi, A. Tsukamoto, H. Wadati, A. Sekiyama, C. M. Schneider, M. Tsunoda, S. Suga, and T. Kinoshita, Investigation of deterministic and cumulative nature in helicity-dependent optical switching of ferrimagnetic Gd–Fe–Co films, Journal of Magnetism and Magnetic Materials 593, 171854 (2024)
https://doi.org/10.1016/j.jmmm.2024.171854

U. Parlak, R. Adam, D. E. Bürgler, T. Duchoň, S. Nemšák, F. Wang, C. Greb, S. Heidtfeld, and C. M. Schneider, Ferromagnetic domain wall manipulation using optically induced thermal gradients, Journal of Magnetism and Magnetic Materials 560, 169441 (2022)
https://doi.org/10.1016/j.jmmm.2022.169441

U. Parlak, R. Adam, D. E. Bürgler, S. Gang, and C. M. Schneider, Optically induced magnetization reversal in [Co/Pt]N multilayers: Role of domain wall dynamics, Phys. Rev. B 98, 214443 (2018)
https://doi.org/10.1103/PhysRevB.98.214443

T. Ohkochi, H. Fujiwara, M. Kotsugi, H. Takahashi, R. Adam, A. Sekiyama, T. Nakamura, A. Tsukamoto, C. M. Schneider, H. Kuroda, E. F. Arguelles, M. Sakaue, H. Kasai, M. Tsunoda, S. Suga, and T. Kinoshita, Optical control of magnetization dynamics in Gd–Fe–Co films with different compositions, Applied Physics Express 10, 103002 (2017)
https://doi.org/10.7567/APEX.10.103002

Last Modified: 11.02.2025