Spin-Orbit Torque-Driven Magnetic Switching of Co/Pt-CoFeB Exchange Spring Ferromagnets

We experimentally investigate spin-orbit torque (SOT) switching of a hybrid exchange spring system (ESS) in which a Co/Pt with perpendicular magnetic anisotropy (PMA) is coupled to a CoFeB thin film with an in-plane (IP) magnetic anisotropy (IMA). The magnetization tilt angle from the out-of-plane can be easily tuned by varying the thickness of the IMA layer due to the competition between PMA and IMA layers. We find that the tilt angle is highly tuned from 0 degrees to 90 degrees over a small range of CoFeB thicknesses, from 0 to 1 nm. The tilted films with high thermal stability are promising materials for a zero/low field operating SOT magnetic random access memory (MRAM) or for a bit patterned magnetic recording media. IP current-induced magnetization switching of Co/Pt-CoFeB ESS is also studied, under an IP magnetic field (H-IP). The current amplitude for the 45 degrees tilt magnetization switching is almost independent of the H-IP ranged from 50 to 1000 Oe. This phenomenon might be due to the presence of the Dzyaloshinskii-Moriya interaction (DMI) and DMI effective field is expected to be less than 50 Oe.