Ferrimagnetic Dynamics Induced by Spin‐Orbit Torques

Abstract Ferrimagnets are the magnetic materials with the fastest current‐induced dynamics reported so far. Among them, rare‐earth transition‐metal (RE‐TM) alloys offer a fertile playground for studying the behavior of multi‐sublattice systems with tunable composition and magnetic interactions. This review provides a survey of the magnetic dynamics excited by current‐induced spin‐orbit torques (SOTs) in RE‐TM ferrimagnets coupled to heavy‐metal layers. It summarizes the magnetic properties of RE‐TM alloys and discusses how interfacial SOTs result in efficient magnetization switching and fast domain‐wall motion close to the magnetization and angular momentum compensation points. Recent work shows that the switching is a multiphase process affected by significant stochastic fluctuations. However, strong SOTs results in fast and deterministic sub‐ns switching with minimal energy dissipation. In addition, the RE and TM magnetizations can respond asynchronously to SOTs during the reversal. This asynchronous dynamics pinpoints the different strength of the SOTs acting on the two sublattices and challenges the usual assumption of rigid inter‐sublattice antiferromagnetic coupling. Overall, the ability to tailor the timescale and reversal mode of RE‐TM alloys allows for optimizing the speed of ferrimagnetic spintronic devices and provides insight into the current‐induced transfer of angular momentum in systems with synergistic ferromagnetic and antiferromagnetic interactions.