Spin-orbit torques and their associated effective fields from gigahertz to terahertz

Terahertz spintronics offers the prospect of devices which are both faster and more energy-efficient. A promising route to achieve this goal is to exploit current-induced spin-orbit torques. However, the high-frequency properties of these quantities remain unexplored both experimentally and theoretically, within a realistic material-specific approach. Here we investigate the dynamical transverse components of the torques and uncover contributions longitudinal to the magnetic moment capable of changing its magnitude. We show that, while the torques can be drastically altered in the dynamical regime, the effective magnetic fields that accompany them present a frequency-independent behaviour, ranging from the static limit up to the terahertz domain — including the ferromagnetic resonance of the system. The outcomes of this work point to new ways to control magnetic units in next-generation spintronic devices. Spintronic devices which are able to function at the terahertz frequency range are desired to help design quicker and more energy efficient apparatus. Here, the authors use simulations to demonstrate that the spin-orbit torque exhibits highly frequency dependent properties which can reveal the magnetisation dynamics of heavy metal/ferromagnetic heterostructures.