"The Quest for Ultrafast, Ultra-Low Energy Magnetization Switching: From Spin-Orbit Coupling to Momentum-Dependent Spin Polarization"

Presented by Dr. Weigang Wang, Professor, University of Arizona

Ultrafast and ultra-low Energy spin manipulation in magnetoresistive devices remains a central challenge in spintronics research. In ferromagnetic systems, switching dynamics are typically governed by the Landau-Lifshitz-Gilbert (LLG) equation, occurring on nanosecond timescales. Spin-transfer torque (STT), spin-orbit torque (SOT), and voltage-controlled magnetic anisotropy (VCMA) are the primary mechanisms driving magnetization switching. In contrast, ferrimagnetic systems can exhibit ultrafast demagnetization through the excitation of strongly nonequilibrium states. These dynamics go well beyond the scope of the LLG framework, enabling full magnetization reversal on picosecond timescales. Meanwhile, recent theoretical predictions suggest that collinear and noncollinear antiferromagnets can host momentum-dependent spin polarization and exhibit large tunneling magnetoresistance. The discovery of rich physics in altermagnetic materials has renewed interest in systems with compensated magnetization. In this talk, I will present our research efforts toward realizing ultrafast, energy-efficient switching across ferromagnetic, ferrimagnetic, and antiferromagnetic systems. By enhancing spin-orbit coupling without sacrificing magnetoresistance—via a remote doping technique—we have achieved a record-low switching energy of ~3 fJ using 500-ps voltage pulses. Despite reduced magnetoresistance in materials with partial or full magnetization compensation, our initial studies show very promising results where ultrafast switching can be potentially achieved in these systems.