Femtosecond Spectroscopy and Spin Dynamics

Femtosecond Spin Dynamics
Figure left: pump-probe experiment schematics using red pump (1.5 eV) and blue probe pulse (3 eV). Optical pulses are generated by a femtosecond laser amplifier operating at 1 kHz repetition rate. Right: dependence of the time-resolved magneto-optic Kerr response M(t) of a [Co/Pt]3 multilayer on the optical pump fluence, measured at constant external magnetic field µH = 100 mT.

We investigate the spin dynamics by tracking time evolution of the magnetization of a material under test after ultrafast optical excitation by a laser. We probe the magnetic response at a central wavelength of 400 nm (3 eV) using the magneto-optical Kerr effect (MOKE) in longitudinal or polar geometry, while the excitation of the electron system is carried out at a central wavelength of 800 nm (1.5 eV).

A femtosecond laser amplifier system with pulse energies of up to 1 mJ, a repetition rate of 1 kHz and pulse durations down to 50 fs is used as a light source. The mirror alignment can be easily switched between polar and longitudinal geometries in order to address either the out-of-plane or in-plane components of the magnetization.

The experiment provides access to femtosecond magnetization dynamics in the valence and conduction bands of 3d transition metals and their alloys, magnetic multilayer systems, as well as novel rare earth–transition metal materials with a temporal resolution below 100 fs.

Publications

X. Chen, R. Adam, D. E. Bürgler, F. Wang, Z. Lu, L. Pan, S. Heidtfeld, C. Greb, M. Liu, Q. Liu, J. Wang, C. M. Schneider, and D. Cao, Ultrafast demagnetization in ferromagnetic materials: Origins and progress, Physics Reports 1102, 1 (2025)
https://doi.org/10.1016/j.physrep.2024.10.008

F. Wang, D. E. Bürgler, R. Adam, U. Parlak, D. Cao, C. Greb, S. Heidtfeld, and C. M. Schneider, Magnetization relaxation dynamics in [Co/Pt]3 multilayers on pico- and nanosecond timescales, Phys. Rev. Research 3, 033061 (2021)
https://doi.org/10.1103/PhysRevResearch.3.033061

M. Liu, S. Du, F. Wang, R. Adam, Q. Li, X. Ma, X. Guo, X. Chen, J. Yu, Y. Song, J. Xu,
S. Li, and D. Cao, Influence of surface pinning in the domain on the magnetization dynamics in permalloy striped domain films, Journal of Alloys and Compounds 869, 159327 (2021)
https://doi.org/10.1016/j.jallcom.2021.159327

D. Cao, R. Adam, D. E. Bürgler, F. Wang, C. Song, S. Li, M. Mikulics, H. Hardtdegen, S. Heidtfeld, C. Greb, and C. M. Schneider, Coherent GHz lattice and magnetization excitations in thin epitaxial Ag/Fe/Cr/Fe films, Phys. Rev. B 104, 054430 (2021)
https://doi.org/10.1103/PhysRevB.104.054430

Last Modified: 11.02.2025