Subnanosecond in-plane magnetization switching induced by fieldlike spin-orbit torques from ferromagnets

Spin-orbit torques (SOTs) generated in SOT-material/ferromagnet structures are classified as dampinglike (DL) and fieldlike (FL) torques for current-driven magnetization switching. It is well-known that both DL- and FL-SOTs originate from the SOT material and DL-SOT dominates the current-driven switching process while FL-SOT has a limited contribution, resulting in an incubation time (several nanoseconds) during collinear magnetization switching with the spin polarization because of the DL attributes. Here, we report that an FL-SOT originates from the ferromagnet, which is different from the origin of DL-SOT, and demonstrate that it dominates the collinear magnetization switching. We show that the FL-SOT and resultant collinear switching can be modulated, by one order of magnitude and a sign reversal, by controlling the ferromagnet. Because of no incubation time and higher charge-to-spin efficiencies in the FL switching, we also show that the switching time can be as low as 200 ps, with an order of magnitude lower critical switching current density compared with DL switching. These results indicate that FL switching may provide a practical solution for magnetic memory in speed-priority cache applications.