Electrical current pulses can be used to manipulate magnetization efficiently via spin–orbit torques. Pulse durations as short as a few picoseconds have been used to switch the magnetization of ferromagnetic films, reaching the terahertz regime. However, little is known about the reversal mechanisms and energy requirements in the ultrafast switching regime. In this work we quantify the energy cost for magnetization reversal over seven orders of magnitude in pulse duration, in both ferromagnetic and ferrimagnetic samples, bridging quasi-static spintronics and femtomagnetism. To this end, we develop a method to stretch picosecond pulses generated by a photoconductive switch by an order of magnitude. Thereby we can create current pulses from picoseconds to durations approaching the pulse width available with commercial instruments. We show that the energy cost for spin–orbit torque switching decreases by more than an order of magnitude in all samples when the pulse duration enters the picosecond range. We project an energy cost of 9 fJ for a 100 × 100 nm² ferrimagnetic device. Micromagnetic and macrospin simulations unveil a transition from a non-coherent to a coherent magnetization reversal with a strong modification of the magnetization dynamical trajectories as pulse duration is reduced. Our results show the potential for high-speed magnetic spin–orbit torque memories and highlight alternative magnetization reversal pathways at fast timescales.

电流脉冲可用于通过自旋轨道扭矩有效地操纵磁化强度。短至几皮秒的脉冲持续时间已被用于切换铁磁膜的磁化强度，达到太赫兹范围。然而，人们对超快开关机制中的反转机制和能量需求知之甚少。在这项工作中，我们量化了铁磁和亚铁磁样品中磁化反转的能量成本，在脉冲持续时间中超过 7 个数量级，桥接了准静态自旋电子学和飞磁。为此，我们开发了一种方法，可以将光电导开关产生的皮秒脉冲拉伸一个数量级。因此，我们可以产生从皮秒到持续时间接近商用仪器可用的脉冲宽度的电流脉冲。我们表明，当脉冲持续时间进入皮秒范围时，所有样本中自旋-轨道扭矩切换的能量成本都降低了一个数量级以上。我们预计 100 × 100 nm² 亚铁磁器件的能源成本为 9 fJ。微磁和宏观自旋仿真揭示了从非相干到相干磁化反转的转变，随着脉冲持续时间的缩短，磁化动力学轨迹发生了强烈变化。我们的结果显示了高速磁自旋轨道扭矩记忆的潜力，并突出了快速时间尺度上的替代磁化反转路径。