报告题目：All-Optical Helicity-Dependent switching in magnetic nano-structures and devices

报 告 人：S. Mangin，Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, France

报告时间：2016年10月21日上午9点

报告地点：理科楼C302报告厅

报告摘要：Since Beaurepaire et al’s observation of ultrafast demagnetization in Ni films arising from a pulsed laser excitation [1], there has been a drive to understand the interaction between the ultrashort laser pulses and magnetization. These studies led to the discovery of the “All-Optical Switching” of magnetization in a ferromagnetic film alloy of GdFeCo using femtosecond laser pulses [2]. All Optical switching leads to a deterministic magnetization reversal of the material with no external magnetic field; the direction of the resulting magnetization is given by the right or left circular polarization of the light.

The manipulation of magnetization through laser beam had long been restricted to one material, though it turned out to be a more general phenomenon for a variety of ferromagnetic materials; including alloys, multilayers and heterostructures, as well as rare earth free synthetic ferrimagnetic heterostructures [3]. Recently, we have observe the same phenomenon in single ferromagnetic films, thus paving the way for an integration of the all-optical writing in storage industries [4].

It is within that context that we are studying the effect of femtosecond laser pulses on magneto-resistive systems with perpendicular magnetic anisotropy, with the aim of identifying the magnetization orientation through an electrical signal. We measure the all-optical switching in Pt/Co/Pt and Tb27Co73 based Hall crosses via the anomalous Hall effect. In fact, a jump in Hall voltage resulting from magnetization reversal is observed by reversing the circular polarization of the femtosecond laser pulses. This new way of probing the all-optical switching enables a statistical quantification of the switching ratio for different laser parameters. We will present results on hall crosses for both ferrimagnetic and ferromagnetic materials [5].

References

[1] E. Beaurepaire et al, Phys. Rev. Lett. 76 (22), 4250-4253 (1996)

[2] C. D. Stanciu et al, Phys. Rev. Lett. 99 047601 (2007); A. Kirilyuk, et al Rev. Mod. Phys. 82, 2731 - 2784 (2010) ; I. Radu, et al., Nature 472, 205 - 208 (2011).

[3] S. Mangin, et al, Nature Materials 13, 286-292 (2014)

[4] C-H. Lambert et al, Science 345 (6202), 1337 (2014)

[5] M.S. El Hadri et al, App. Phys. Lett. 108 , 092405 (2016), Phys. Rev. B 94, 064412 (2016) , Phys. Rev. B 94, 064419 (2016)