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Ultrafast Magnetization Manipulation Using Single Femtosecond Light and Hot-Electron Pulses

Abstract : femto-or picosecond laser pulses [11–13] have motivated numerous theoretical and experimental investigations. The recent discoveries in the field of optically driven magnetization switching have attracted a lot of attention, especially the all optical helicity independent switching (AO-HIS) of GdFeCo using a single femtosecond laser pulse. The exact microscopic mechanisms still need to be understood, but both experimental and theoretical results indicate a pure thermal origin of AO-HIS in GdFeCo. [11,14,15] When driven by AO-HIS, the magnetization switches within 30 ps which allows pushing the speed of the recording technology to high frequencies above 10 GHz. [16] However, within the context of spintronic devices, the mag-netization switching induced by electronic currents and electric fields is particularly interesting and can be easily implemented in nanoscale devices. [17,18] The technological importance of the ultrafast AO-HIS in GdFeCo immediately raised the possibility of obtaining the same reversal speed with a single pulse of hot electrons. This technique could be adapted for nanoscale technologies and open a field of ultrafast-spintronic devices. Hot-electron transport has been recently presented as an alternative way to manipulate spins and has been demonstrated to offer an extensive control of the ultrafast demagneti-zation in metallic multilayers, [19] as initially demonstrated in Ni film by femtosecond laser pulses. [20] Furthermore, spin polarized hot electrons allow control over the speed of demagnetization [21] and even may be used to initiate coherent magnetization preces-sion by STT. [22] More recently, Wilson et al. have shown the possibility to use hot electrons to perform magnetization reversal in GdFeCo. [23] However, the timescale of such a magnetization reversal remains unknown, and this magnetization reversal was only reported for one composition of GdFeCo. These results triggered different fundamental questions: What is the timescale of this switching process? Is it similar to the one reported for the light-induced AO-HIS? Since the demagnetization timescale of rare earth and transition metal magnetic atoms is different, can hot electrons reverse the magnetization in both Gd-rich and FeCo-rich alloys? If yes, are the two reversal timescales similar? And finally, what is the hot-electrons transport mechanism? To answer these questions, we have carefully studied the magnetization dynamics induced by hot electrons and laser Current-induced magnetization manipulation is a key issue for spintronic applications. This manipulation must be fast, deterministic, and nondestruc-tive in order to function in device applications. Therefore, single-electronic-pulse-driven deterministic switching of the magnetization on the picosecond timescale represents a major step toward future developments of ultrafast spintronic systems. Here, the ultrafast magnetization dynamics in engineered Gd x [FeCo] 1−x-based structures are studied to compare the effect of femto-second laser and hot-electron pulses. It is demonstrated that a single fem-tosecond hot-electron pulse causes deterministic magnetization reversal in either Gd-rich and FeCo-rich alloys similarly to a femtosecond laser pulse. In addition, it is shown that the limiting factor of such manipulation for perpendicular magnetized films arises from the formation of a multidomain state due to dipolar interactions. By performing time-resolved measurements under various magnetic fields, it is demonstrated that the same magnetiza-tion dynamics are observed for both light and hot-electron excitation, and that the full magnetization reversal takes place within 40 ps. The efficiency of the ultrafast current-induced magnetization manipulation is enhanced due to the ballistic transport of hot electrons before reaching the GdFeCo magnetic layer. Spintronics Energy-efficient ultrafast magnetization manipulation in the absence of external applied magnetic field is of utmost importance for both future spintronic applications and a fundamental understanding of ultrafast magnetization dynamics. Modern magnetics research focuses on the dynamic response of magnetic order to an ultrafast external excitation. [1] Moreover , an efficient means of magnetization manipulation is of prime importance for information and memory storage devices. During the last 10 years the effect of spin-transfer torque (STT), [2–5] spin–orbit torque, [6,7] electric field, [8–10] and
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Submitted on : Wednesday, January 17, 2018 - 11:21:42 PM
Last modification on : Monday, April 6, 2020 - 2:44:04 PM



Yong Xu, Marwan Deb, Grégory Malinowski, Michel Hehn, Weisheng Zhao, et al.. Ultrafast Magnetization Manipulation Using Single Femtosecond Light and Hot-Electron Pulses. Advanced Materials, Wiley-VCH Verlag, 2017, 29 (42), pp.1703474 - 1703474. ⟨10.1002/adma.201703474⟩. ⟨hal-01686942⟩



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