Thema der Dissertation:
Magnon polarons and spin transport investigated by time- and spin-resolved photoelectron spectroscopy
Magnon polarons and spin transport investigated by time- and spin-resolved photoelectron spectroscopy
Abstract: Magnons and phonons are quanta of spin waves and lattice vibrations, respectively. They can be strongly hybridized to form magnon polarons, because of large magnetoelastic coupling in magnetic materials. This phenomenon was evidenced in neutron diffraction experiments revealing avoided crossings between the phonon and magnon branches. We used spin-resolved photoemission spectroscopy to investigate gadolinium and terbium. Both ferromagnetic rare earth metals have a comparable valence electronic structure but Gd is more like a Heisenberg ferromagnet where anisotropy is weak, while Tb holds much stronger magnetoscrystalline anisotropy. We found that magnon polarons play a crucial role in photohole relaxation in Tb due to the strong 4f spin-orbit coupling. The latter is very weak in Gd. Consequently, electron-phonon and electron-magnon scatterings lead to spin-dependent photohole relaxation rates in Gd. In contrast, the lifetime broadening of the occupied surface state in Tb is only weakly spin dependent and the mass enhancement parameter is twice the spin-averaged value of Gd. The formation of magnon polarons in Tb opens both minority and majority spin bands as decay channels.
Besides local scattering processes driving ultrafast demagnetization, ultrafast spin transport is of enormous importance for understanding the mechanisms of many spin-dependent effects. Investigating laser-induced spin transport helps to obtain microscopic insights into ultrafast spin dynamics, and to fabricate high efficiency spintronics. We used time- and spin-resolved photoelectron spectroscopy to study an antiferromagnetically coupled Gd/Fe bilayer and observed an ultrafast 20% decrease of the spin polarization of the Gd surface state within the first 100 fs after optical excitation. The result was confirmed by a transient increase of the spin polarization in iron and corroborated by a decrease of the transient electron temperature. We conclude that spin transport across the interface drives magnetization dynamics in the Gd/Fe bilayer system. Fe acts as a very efficient spin-filter for spin-minority electrons. These findings contribute to a microscopic understanding of ultrafast spin dynamics and possible future spintronic applications.
Besides local scattering processes driving ultrafast demagnetization, ultrafast spin transport is of enormous importance for understanding the mechanisms of many spin-dependent effects. Investigating laser-induced spin transport helps to obtain microscopic insights into ultrafast spin dynamics, and to fabricate high efficiency spintronics. We used time- and spin-resolved photoelectron spectroscopy to study an antiferromagnetically coupled Gd/Fe bilayer and observed an ultrafast 20% decrease of the spin polarization of the Gd surface state within the first 100 fs after optical excitation. The result was confirmed by a transient increase of the spin polarization in iron and corroborated by a decrease of the transient electron temperature. We conclude that spin transport across the interface drives magnetization dynamics in the Gd/Fe bilayer system. Fe acts as a very efficient spin-filter for spin-minority electrons. These findings contribute to a microscopic understanding of ultrafast spin dynamics and possible future spintronic applications.
Time & Location
Aug 15, 2025 | 03:30 PM
Hörsaal B (0.1.01)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)