Ultrashort spin–orbit torque generated by femtosecond laser pulses

Abstract

To realize the very objective of spintronics, namely the development of ultra-high frequency and energy-efficient electronic devices, an ultrafast and scalable approach to switch magnetic bits is required. Magnetization switching with spin currents generated by the spin–orbit interaction at ferromagnetic/non-magnetic interfaces is one of such scalable approaches, where the ultimate switching speed is limited by the Larmor precession frequency. Understanding the magnetization precession dynamics induced by spin–orbit torques (SOTs) is therefore of great importance. Here we demonstrate generation of ultrashort SOT pulses that excite Larmor precession at an epitaxial Fe/GaAs interface by converting femtosecond laser pulses into high-amplitude current pulses in an electrically biased p-i-n photodiode. We control the polarity, amplitude, and duration of the current pulses and, most importantly, also their propagation direction with respect to the crystal orientation. The SOT origin of the excited Larmor precession was revealed by a detailed analysis of the precession phase and amplitude at different experimental conditions.

Perspectives: Light Control of Magnetism and Device Development

“…Janda et al has developed a method to generate ultrafast spin−orbit torque pulses at a ferromagnetic metal−semiconductor interface. 183 By converting femtosecond laser pulses into high-amplitude current pulses in an iron−gallium−arsenide photodiode, they initiated the precession of iron's magnetization directly at the interface, as shown in Figure 8d. This technique suggested the potential for rapid magnetic order changes in antiferromagnetic films.…”

“…Differential photocurrent responses at positions (i) and (iii) due to annular Au contact placement and absence of lateral photocurrent at position (ii). Reprinted with permission under a Creative Commons CC BY license from ref . Copyright 2022, Janda et al (f) Schematic of TRMOKE measurement setup showing the structure of the Co 2 FeAl/(Ga,Mn)As bilayer sample and magnetization processing around the effective field H eff in a canted magnetization configuration.…”

Thermally induced all-optical ferromagnetic resonance in thin YIG films

“…In principle, also the spin-Seebeck effect [5,6] can be a source of the torque. Each of these phenomena shows certain fingerprints, yet the most dominant is their relevant timescale, which limits how fast the dynamics can be triggered and leads to a characteristic phase of the magnetization precession (see supplementary note 1 in [44]). However, a straightforward analysis of the phase is only possible if the polar Kerr effect dominates magneto-optical response of the studied system.…”

“…figure 2 in [14] and figure 1(d) in [15]), and we can exclude them by the relatively long ≈ 20 ps onset of the precession in our signals. On the other hand, the thermal effects are known to be significantly slower [15,44] and they share one particular finger print-the torque induced by thermal modification of magnetic properties is typically strongly dependent on the applied external magnetic field (see the discussion in supplementary note 1 in [44]). In figure 4(a) we show the amplitude A of the oscillatory part of the TRMO signal as a function of the external magnetic field H ext .…”

Photocurrents, inverse Faraday effect and photospin Hall effect in Mn$_2$Au

“…As a consequence, optical manipulation and in particular the read-out of the Néel vector during optical dynamics in antiferromagnets becomes a matter of grave importance 10,11 . In this context, the properties of optically generated photocurrents come to occupy a special place [12][13][14][15][16] . Some of major promises of antiferromagnetic spintronics hinge on our ability to get a control over the properties and timescales of ultrafast antiferromagnetic dynamics triggered by optical excitations.…”