MBI Colloquium
Wednesday, 22. May 2024 // 14.00 -
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy
Max-Born-Straße 2a,
12489 Berlin
Max Born Hall
Dynamics of magnetic structures on picosecond time scales probed via resonant magnetic scattering at FERMI
Prof. Dr. Christian Gutt | University of Siegen
We are interested in the temporal response of magnetic structures upon excitation by short pulses of IR and XUV radiation. Employing circularly polarized light pulses from an XUV FEL we investigated the evolution of the chirality of domain walls in magnetic thin film samples. Using samples exhibiting labyrinth-like domain patterns, we measured in the same experiment both the sum signal corresponding to the ferromagnetic order in the domains and the difference signal corresponding to the average chiral order in the domain walls. We observed an ultrafast intensity decrease of both signals in the sub-ps regime with similar time constants and a significantly faster recovery of the chiral signal in the sub-ns timescale [1]. Follow-up experiments employing different domain sizes demonstrated more complex interactions on 50-200 ps timescales between the chiral / collinear magnetic order and surface acoustic structures and waves launched by the IR pulses [2].
We also utilized XUV pulses to generate transient periodic magnetization patterns with periods as short as 44 nm [3]. Combining spatially periodic excitation with resonant probing at the M-edge of cobalt allowed us to create and probe transient gratings of electronic and magnetic excitations in a CoGd alloy. In a demagnetized sample, we observe an electronic excitation with a rise time close to the FEL pulse duration and ∼0.5 ps decay time indicative of electron–phonon relaxation. When the sample is magnetized to saturation in an external field, we observe a magnetization grating, which appears on a subpicosecond time scale as the sample is demagnetized at the maxima of the XUV intensity and then decays on the time scale of tens of picoseconds via thermal diffusion. The described approach opens multiple avenues for studying dynamics of ultrafast magnetic phenomena on nanometer length scales. I will also report on XUV transient grating experiments with coherent magnons in Fe/Gd ferrimagnetic multilayers. Magnons with tens of nanometers wavelengths were excited by a pair of femtosecond XUV pulses and detected via diffraction of a probe pulse tuned to an absorption edge of Gd [4].
[1] N. Kerber et al. Nat Commun 11, 6304 (2020)
[2] D. Ksenzov et al. to be published.
[3] D. Ksenzov et al. Nano Lett. 21, 2905 (2021)
[4] P. Miedaner et al. - submitted