Time: Tuesday, October 23rd, 11:20
Speaker: Kihiro YAMADA, Nijmegen
Ultrafast magnetization switching with an ultra-short laser pulse attracts much attention for future applications for magnetic recording, operating with low energy consumption and at high speed. Since the pioneering work in ferrimagnetic GdFeCo [1], various systems have been tested, including metals [2], semiconductors [3], and insulators [4]. Recently, it has been demonstrated that also ferromagnetic multilayers display all-optical helicity-dependent switching (AO-HDS) [5], i.e., the magnetization can be controlled using circularly-polarized laser pulses. However, to observe switching, many pulses were required [6]. Here, we demonstrate that the number of pulses required for AO-HDS can be dramatically reduced by using a dual-pulse method. In the experiment, we used a single stack of Pt (3 nm)/Co (0.6 nm)/Pt (3 nm) with perpendicular magnetic anisotropy, which is very widely used for static as well as ultra-fast experiments in spintronics. In order to fully flip the magnetization, we used two pulses fulfilling different roles: the first short (70 fs) linearly-polarized laser pulse for demagnetizing and the second longer (3 ps) circularly-polarized laser pulse for switching. Five such pairs of pulses fully flip the magnetization for a time separation between the two laser pulses of 2 ps, and the fluence of the first and second laser pulse of 2.29 and 1.94 mJ/cm2, respectively. In stark contrast, using only long circularly polarized laser pulses, 100-150 pulses are still necessary. The results suggest that the dual-pulse method is a potential route towards realizing efficient AO-HDS in ferromagnetic metals on an ultrashort time scale.
[1] C. D. Stanciu et al., Phys. Rev. Lett. 99, 047601(2007). [2] S. Mangin et al., Nat. Mater. 13, 286-292 (2014). [3] A. J. Ramsay et. al., Phys. Rev. Lett. 114, 067202 (2015). [4] A Stupakiewicz et. al., Nature 542, 71 (2017) [5] C-H. Lambert et al., Science 345, 1337-1340 (2014). [6] R. Medapalli et al., Phys. Rev. B 96, 224421 (2017).