Tutorial: Femto-Second Light and Electron Pulses to switch magnetisation

Time: Thursday, October 25th, 14:00
Speaker: Stephane MANGIN, Nancy

Since the first observation of magnetization switching in ferrimagnetic GdFeCo alloy films using femtosecond laser pulses in 2007 [1],understanding the mechanism behind all-optical switching (AOS) is becoming a topic of huge interest in the magnetism community. Moreover ultrafast magnetization switching in magnetic material thin film without any applied external magnetic field is drawing a lot of attention for the development of future ultrafast and energy efficient magnetic data storage and memories.
Two type of all optical switching have then ben distinguished: Helicity Independent – All Optical Switching (HI- AOS) and Helicity Dependent – All Optical Switching (HD- AOS). HI-AOS has only been demonstrated for GdFeCo based material and is observed after a singlelaser pulse [2]. After one pulse the magnetization is reversed in the opposite direction independently of the light helicity. On the other hand, HD- AOS has been observed for a large variety of magnetic material such as ferrimagnetic alloy, ferrimagnetic multilayer, ferromagnet, and granular media [3-5].  However several studies shows that HD-AOS is only observed after multiple pulses [6].
During the presentation I will present experimental results showing that the number of pulses can be reduced significantly in order to switch ferromagnetic [Co/Pt] multilayers using only several light pulses. Those results can be explained by considering the transfer of heat and angular from light to the sample’s electron bath [7].
In all the previously reported experiments light is used to manipulate magnetization. However, recently we have engineered multilayer structures in order to create hot electrons femto second pulses. We have demonstrate that the magnetization of GdFeCo can be switched using a femto-second hot electron pulse with no direct light interaction [8]  which confirm the work from Wilson et al [9]. Indeed they reported the switching of GdFeCo/Au bilayer via hot electrons generated by single pulse femtosecond laser. Moreover we have studied the magnetization reversal in a GdFeCo / Cu / [Co/Pt] spin valve structure. We observed single shot switching of both the ferrimagnetic GdFeCo and  the ferromagnetic [Co/Pt] layer. The magnetisation switching is found to be mediated by spin polarized hot electron transport [10].


[1] C. D. Stanciu, et al, Phys. Rev. Lett. 99, 047601 (2007).
[2] T. A. Ostler, etal  Nat. Commun. 3, 666 (2012).
[3] S. Alebrand,et al   Appl. Phys. Lett. 101, 162408 (2012)
[4] S. Mangin, et al Nat. Mater. 13, 286 (2014).
[5] C.-H. Lambert, et al , Science 1253493 (2014).
[6 ] M. S. El Hadri et al. Phys. Rev. B 94, 064412 (2016)
[7] G. Kichin et al in Preparation
[8] Y. Xu, et al l Adv Matter 2942 1703474 (2017)
[9]  R. B. Wilson, et al  Physical Review B 95 (18), 180409
[10] S. Iihama et al. Adv Mat (2018)