A setup for element specific magnetization dynamics using the transverse magneto-optic Kerr effect in the energy range of 30-72 eV

Abstract

In this paper, we present a spectrometer that is designed for element-specific and time-resolved transverse magneto-optic Kerr effect experiments at the high-harmonic generation pump-probe facility High Energy Laser Induced Overtone Source (HELIOS) laboratory. HELIOS delivers photons with energies between 30 eV and 72 eV with an overall time resolution of less than 40 fs. The spectrometer is based on a Rowland-circle geometry and allows for simultaneous measurements of all magnetic transition-metal elements. The setup also features easy sample transfer and alignment, and it combines high photon throughput, optimized data acquisition, and a fast switching of the magnetic field at the sample. The spectrometer performance is demonstrated by measuring the ultrafast demagnetization of permalloy. Our data are, for all practical purposes, identical to what have been reported in the earlier high-order harmonic generation work of a similar sample by Mathias et al. [Proc. Natl. Acad. Sci. U. S. A. 109, 4792-4797 (2012)], however, obtained within 15% of the acquisition time compared to their study. Furthermore, our data show a shift of the demagnetization curve of Ni relative to Fe, which has previously been interpreted as a delay of the Ni demagnetization to that of Fe [S. Mathias et al., Proc. Natl. Acad. Sci. U. S. A. 109, 4792-4797 (2012)].

A novel free-electron laser single-pulse Wollaston polarimeter for magneto-dynamical studies

“… 28 and the 220 fs reported in Ref. 29 . We limit our comparison to the demagnetization time, since the recovery time strongly depends on the laser pump fluence and on the Ni x Fe 1− x Permalloy stoichiometry.…”

“…We limit our comparison to the demagnetization time, since the recovery time strongly depends on the laser pump fluence and on the Ni x Fe 1− x Permalloy stoichiometry. 28 A detailed investigation of the demagnetization curve is already subject of existing literature, 29 and it goes beyond the scope of present work.…”

Thresholding of the Elliott-Yafet spin-flip scattering in multi-sublattice magnets by the respective exchange energies

“…We demonstrate that, due to the very fast rise of the electron subsystem temperature, even for low lattice subsystem temperatures, the angular momentum transfer spin-flip channel can be open. More conceptually, one could suppose that different demagnetization mechanisms can also be thresholded, which would help understanding more recent results showing delayed demagnetization in metallic alloys for different components 17,18,37,38 .…”

“…More recently, ultrafast pump-probe methods have been applied to magnetic alloys, where peculiar transient magnetic states were observed, like an ultrashort ferromagnetic alignment in a ferrimagnetic GdFe compound 13 than that of iron and second, the demagnetization of nickel in Fe 50 Ni 50 happens faster than in Fe 20 Ni 80 [14][15][16][17][18][19] . These observations are in contradiction with the microscopic-3TM model, which considers the system as a single macrospin, and therefore, does not distinguish the different elements of the multisublattice.…”

A tabletop setup for ultrafast helicity-dependent and element-specific absorption spectroscopy and scattering in the extreme ultraviolet spectral range

“…[11][12][13] The most prominent geometry for HHG experiments until today exploits the transverse magnetooptical Kerr effect (T-MOKE), where the incident linearly polarized XUV light is reflected off the magnetic sample perpendicularly to the magnetic field direction. 14,15 T-MOKE has gained popularity for two main reasons. First, it does not require additional control of the XUV polarization state, and second, the method offers high magnetic contrast of up to 90% in Fe, 15,16 which allows obtaining sufficiently high signal-to-noise ratios even with highly fluctuating spectral intensities from HHG sources.…”