Current-induced four-state magnetization switching by spin-orbit torques in perpendicular ferromagnetic trilayers

We demonstrated current-induced four-state magnetization switching in a trilayer system using spin-orbit torques. The memory device contains two Co layers with different perpendicular magnetic anisotropy, separated by a spacer layer of Pt. Making use of the opposite spin current at the top and bottom surface of the middle Pt layer, magnetization of both Co layers can be switched oppositely by the spin-orbit torques with different critical switching currents. By changing the current pulse forms through the device, the four magnetic state memory was demonstrated. Our device provides an idea for the design of low power and high density spin-orbit torque devices.