(1.School of Physics and Electronic Science, Hubei University, Wuhan 430062, China) (2.Songshan Lake Materials Laboratory, Dongguan 523808, China) (3.Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China)
Spin-orbit torque (SOT)-based all-electric driven magnetization switching with fast writing speed, high endurance, long service life and low-power consumption has attracted much attention for the potential application in next-generation spintronic memories and logic devices. For conventional SOT-driven perpendicular magnetization switching, an external in-plane magnetic field is inevitable to break the symmetry, which is the main obstacle for practical applications due to its requirement of more power consumption and additional complex design circuits. Thus, the realization of field-free perpendicular magnetization switching by SOT is eagerly desired. Here, we reviewed the recent advances in field-free SOT-driven magnetization switching. The correlated mechanisms include symmetry breaking of the magnetic layer structure, in-plane exchange bias field, modulation of the in-plane anisotropy by electric field regulation, gradient anisotropy in ferrimagnets, and gradient saturation magnetization intensity, etc.