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.

Faculty of Mathematics and Physics Charles University Ke Karlovu 3 121 16 Prague 2 Czech Republic

Institute for Experimental and Applied Physics University of Regensburg Universitätsstr 31 93053 Regensburg Germany

Institute of Physics ASCR v v i Cukrovarnická 10 162 00 Prague 6 Czech Republic

School of Physics and Astronomy University of Nottingham Nottingham NG7 2RD UK

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