Ultra-long spin relaxation in two-dimensional ferromagnet Cr₂Ge₂Te₆ flake

Abstract

By utilizing time-resolved magneto-optical Kerr effect technique, we investigated both demagnetization and remagnetization processes of a typical two-dimensional (2D) van der Waals (vdW) ferromagnetic (FM) semiconductor Cr2Ge2Te6 (CGT) and two comparative Te-based crystals, i.e. three-dimensional (3D) FM metal Cr3Te4 (CT) and 2D vdW FM metal Fe3GeTe2 (FGT). Different from 3D CT showing one-step laser-induced demagnetization, two-steps demagnetization behavior is dominated in 2D vdW FGT and CGT, which indicates that the 2D vdW magnets have relatively weaker electron-spin coupling. Of particular interest, we discovered an ultra-long remagnetization behavior in the 2D vdW CGT flake. The laser pumping induced spin demagnetization would not recover even in the time scale of 3500 ps (experimental setup limitation). To the best of our knowledge, this is the longest remagnetization process observed so far and it might be one of the particular characterizations of 2D vdW ferromagnet semiconductors. Based on the modified three temperature model, the key roles played by the crystal dimensionality and thermal diffusion anisotropy were revealed in the spin dynamics of 2D vdW magnets. Our findings would not only open the door to the thoroughly understanding of the origin of the magnetism in 2D FM materials but also undoubtedly find suitable applications in spintronics and magnonics devices.

Anisotropic laser-pulse-induced magnetization dynamics in van der Waals magnet Fe3GeTe2

“…The laser-induced demagnetization is found to be strongly dependent on an applied in-plane magnetic field, consistent with an anisotropy in the spin-flip probability, which has been predicted for other material classes [29,30]. Moreover, contrary to recent studies in Cr 2 Ge 2 Te 6 (CGT) [20], we were unable to excite ferromagnetic resonance (FMR) modes. We hypothesize that this is caused by strong dephasing of the FMR mode due to weak interlayer coupling and in-plane anisotropy variations.…”

“…This leads to the excitation of damped precessional dynamics. Even though FMR modes have been shown for a similar material-CGT, which possesses a much lower perpendicular magnetic anisotropy (PMA) [20]in a similar experimental configuration, we do not observe any signs of magnetization precession in our measurements. We explain the absence of the FMR mode in our experiments (figure 4(a)) by the weak interlayer exchange coupling A ex,⊥ due to the vdW stacking in FGT [28,62,63].…”

Laser-induced topological spin switching in a 2D van der Waals magnet

“…This is a two-stage demagnetisation process defined as a type-II dynamics 51 . Indeed, this result is in good agreement with recent time-resolved magneto-optical Kerr effect measurements 42 at similar energy fluence.…”

“…Nevertheless, the use of light probes such ultrafast laser pulses to generate and manipulate topological spin textures on 2D vdW compounds is currently unknown. There have been recent reports on pump probe measurements on 2D magnets [42][43][44] , but the demonstration of the formation of spin textures via ultrafast laser excitations is yet to be reported.…”

Two-dimensional chalcogenide-based ferromagnetic semiconductors

“…In addition, the bulk CrXTe 3 single crystal also exhibit some novel physical phenomena, such as existence of a two-step magnetic order in the anisotropy of CrXTe 3 [85], an insulator-metal and structural transition at 7.5 GPa in CrSiTe 3 [160], multiple domain structure and symmetry types in CrGeTe 3 [144], coexistence of large positive magnetoresistance and negative magnetoresistance in CrSiTe 3 [161], ultra-long remagnetization behavior in the CrGeTe 3 [162], phonon-related magneto-tunable monochromatic THz irradiation [145].…”