Field-Free switching of perpendicular magnetization through spin-orbit torque in FePt/[TiN/NiFe]5 multilayers

In order to maintain thermal stability of SOT devices with nanoscale size, it is desirable to achieve current induced magnetic switching in magnetic materials with high perpendicular anisotropy. In the present paper, current induced field-free switching of FePt/[TiN/NiFe]5 is achieved by interlayer exchange coupling, in which in-plane magnetized NiFe is served as coupled layer through a TiN space layer. The large Ku (1.03×107 erg/cc) and low critical current density (0.17×107 A/cm2) show great advantages in thermal stability as well as energy consumption. Interestingly, it is found the rotation directions of the current-induced magnetic switching loops under different applied magnetic fields are dependent on sputtering temperature of [TiN/NiFe]5 multilayers: once sign change for FePt/[TiN/NiFe]5 RT and three times sign changes for FePt/[TiN/NiFe]5 HT. Simultaneously, when the magnetization direction of NiFe changes from Hx direction to - Hx direction, the switching polarities at Hx=0 always remain unchanged, which is different from other groups’ reports. These phenomena may be attributed to the combined effect of TiN layer thickness induced ferromagnetic or antiferromagnetic coupling and the inherent Hin. Furthermore, the gradual tuning of resistance states through trains of current pulses has also been realized, showing the potential application in artificial synaptic networks. These results will put forward the application of L10-FePt in current controlled MRAM as well as neuromorphic computing.