Séminaire LCPMR | Quentin Remy "Sub-picosecond magnetization reversal of ferromagnets..."

Abstract:Since the discovery of ultrafast demagnetization of ferromagnets in 1996 [1], the ultrafast magnetism community had to face many theoretical and experimental challenges to trigger and observe various types of ultrafast (sub-picosecond) spin dynamics as well as to understand their underlying mechanisms. While many questions are still open [2], the specific topic of magnetization reversal (also called switching) is of great fundamental interest, to understand for example magnetization dynamics in the nonlinear regime and the dynamics of phase transitions, on top of its potential applications for data storage devices.
In this seminar, I will present how one can reverse the magnetization of ferromagnets using external spin currents coming from the laser-pulse induced demagnetization of a ferrimagnetic GdFeCo layer [3]. The bipolar temporal shape of the spin current is seen to control the dynamics of the magnetization of the ferromagnet when the latter is nearly quenched [4] leading to a magnetization switching within a few hundred of femtoseconds. Finally, I will show that one can design a simple fully ferromagnetic heterostructure (free of rare-earth materials) where the direction of the magnetization is dictated by the laser pulse energy [5]. These results are supported by a model which supports a complex interplay between magnetization dynamics and spin transport [6].  

[1] E. Beaurepaire, J.-C. Merle, A. Daunois, and J.-Y. Bigot, Phys. Rev. Lett. 76, 4250 (1996).
[2] P. Scheid, Q. Remy, S. Lebègue, G. Malinowski, and S. Mangin, J. Magn. Magn. Mater. 560, 169596 (2022).
[3] S. Iihama et al., Adv. Mater. 30, 1804004 (2018); Q. Remy et al., Adv. Sci. 7, 2001996 (2020); J. Igarashi et al., Nano Lett. 20, 8654 (2020).
[4] Q. Remy et al., Nat. Commun. 14, 445 (2023).
[5] J. Igarashi et al., Nat. Mater. (2023).
[6] Q. Remy, Phys. Rev. B 107 174431 (2023).