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Ultrafast magnetization switching at picosecond and sub-picosecond time scales has tremendous technological potential but still poses numerous questions regarding the underlying quantum mechanical phenomena, including the roles of and interactions between the electrons, spins, and phonons (lattice). At the nanometer-scale dimensions relevant for modern applications, these phenomena become increasingly more pronounced. Until now, helicity-independent all-optical switching (HI-AOS) has been largely limited to amorphous Gd-Fe-Co alloys, for which scaling was challenging due to their relatively low anisotropies. In this work, we demonstrate HI-AOS in amorphous GdCo and scale it to nanometer dimensions while still maintaining uniform out-of-plane magnetization. Single shot HI-AOS is demonstrated in these patterned samples down to a minimum optically detectable magnetic dot size of 200 nm. The ultrafast switching behavior was also confirmed using time-resolved magneto-optic Kerr effect measurements and found to settle to its opposite magnetization state at faster rates for smaller dot diameters, passing a threshold of 75% magnetization reversal within approximately 2 ps for a 200 nm dot compared to approximately 40 ps for a 15 μm pattern. The size dependence of the ultrafast switching is explained in terms of the electron-phonon and spin-lattice interactions. [ABSTRACT FROM AUTHOR]

We report the magnetic response of Co/Pt multilayers to picosecond electrical heating. Using photoconductive Auston switches, we generate electrical pulses with 5.5 ps duration and hundreds of pico-Joules to pass through Co/Pt multilayers. The electrical pulse heats the electrons in the Co/Pt multilayers and causes an ultrafast reduction in the magnetic moment. A comparison between optical and electrically induced demagnetization of the Co/Pt multilayers reveals significantly different dynamics for optical vs electrical heating. We attribute the disparate dynamics to the dependence of the electron-phonon interaction on the average energy and the total number of initially excited electrons. [ABSTRACT FROM AUTHOR]