Ultraschnelle Magnetisierungsdynamik in Perovskit Filmen und Heterostrukturen
Zusammenfassung der Projektergebnisse
Within the scope of the project a novel setup for measuring element/energy-resolved spin dynamics using the transversal magneto-optical Kerr effect (T-MOKE) in the extreme ultraviolet spectral region was developed based on a high repetition rate fiber laser amplifier and high harmonic generation in a gas jet. This setup allows for an order of magnitude improvement in signal quality and long-term stability compared to standard implementations using Ti:Sapphire-based femtosecond amplifiers and HHG generation in a capillary. Using this setup, a straightforward methodology was developed to extract the time- and energy-resolved off-diagonal element of the dielectric tensor, as well as the time- and energyresolved refractive index of magnetic sample systems, allowing for a full characterization of the charge and spin dynamics of the system under study and facilitating a quantitative comparison with ab-initio time-dependent density functional theory. This methodology is based on short-range angle scans of the magnetic asymmetry across the respective M-edge resonances, which can be easily implemented into typical EUV spectroscopy setups. The development of this methodology within the project was precipitated by the surprising experimental observation of strongly varying spin dynamics in the energy-resolved magnetic asymmetry of 3d-ferromagnets depending on the EUV probe energy, namely an increase, delay or decrease of the transient asymmetry signal for the same probe energy by slight variations of the incidence angle of light onto the sample. As an increase in magnetic asymmetry at certain energies is the main signature of the recently discovered optically induced intersite spin transfer (OISTR), the developed methodology was used within the scope of the project to re-verify the existence of OISTR. In general, the results obtained in this part of the project are highly relevant for any magneto-optic technique in the EUV/soft X-ray region, especially since the physics leading to spectrally resolved dynamics has received considerable attention in the last years. In addition to exploring the relation between spin dynamics and magnetooptical signals in general, this project aimed at studying spin dynamics in correlated oxides with the goal to design sample systems suitable to transiently photoinduce ferromagnetism. Here, one basic approach was to photo-dope manganites, e.g., La1-xSrxMnO3 (LSMO) with x<0.3 or La-deficient La1-δMnO3 (LMO) to control the Mn3+/Mn4+ ratio by ultrafast laser-excitation of Mn3+ ions destroying the Jahn-Teller distortion of Mn3+ octahedra, i.e., control the number of holes in the system. This promotes the double exchange mechanism in these materials potentially leading to metallization and ferromagnetic order. For both LSMO and LMO with tuned doping signs of nonthermal reflectivity transients, as well as long-living nanosecond positive MOKE transients were observed, indicating that indeed a metallization and ferromagnetic order are generated in these systems due to the photo-doping of holes.
Projektbezogene Publikationen (Auswahl)
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Ultrafast element-resolved magneto-optics using a fiber-laser-driven extreme ultraviolet light source. Review of Scientific Instruments, 92(6).
Möller, Christina; Probst, Henrike; Otto, Johannes; Stroh, Karen; Mahn, Carsten; Steil, Sabine; Moshnyaga, Vasily; Jansen, G. S. Matthijs; Steil, Daniel & Mathias, Stefan
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Energy relaxation in (La0.6Pr0.4)0.7Ca0.3MnO3 films across the metal-insulator transition. Physical Review B, 107(8).
Seick, Cinja; Stroh, Karen; Titze, Tim; Bruchmann-Bamberg, Vitaly; Weisser, Andreas; Mathias, Stefan; Moshnyaga, Vasily; Ulrichs, Henning & Steil, Daniel
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Unraveling femtosecond spin and charge dynamics with extreme ultraviolet transverse MOKE spectroscopy. Physical Review Research, 6(1).
Probst, Henrike; Möller, Christina; Schumacher, Maren; Brede, Thomas; Dewhurst, John Kay; Reutzel, Marcel; Steil, Daniel; Sharma, Sangeeta; Jansen, G. S. Matthijs & Mathias, Stefan
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Verification of ultrafast spin transfer effects in iron-nickel alloys. Communications Physics, 7(1).
Möller, Christina; Probst, Henrike; Jansen, G. S. Matthijs; Schumacher, Maren; Brede, Mariana; Dewhurst, John Kay; Reutzel, Marcel; Steil, Daniel; Sharma, Sangeeta & Mathias, Stefan
