Spin-torque memristors based on perpendicular magnetic tunnel junctions with a hybrid chiral texture

Spin-torque memristors were proposed in 2009, which could provide fast, low-power and infinite memristive behavior for large-density non-volatile memory and neuromorphic computing. However, the strict requirements of combining high magnetoresistance, stable intermediate states and spin-polarized current switching in a single device pose difficulties in physical implementation. Here, we experimentally demonstrate a nanoscale spin-torque memristor based on a perpendicular-anisotropy magnetic tunnel junction with a CoFeB/W/CoFeB composite free layer structure. Its tunneling magnetoresistance is higher than 200%, and memristive behavior can be realized by spin-transfer torque switching. Memristive states are maintained by robust domain wall pinning around clusters of W atoms, where nanoscale vertical chiral spin textures could be formed through the competition between opposing Dzyaloshinskii-Moriya interactions and the fluctuating interlayer coupling caused by the Ruderman-Kittel-Kasuya-Yosida interaction between the two CoFeB free layers. Spike-timing-dependent plasticity is also demonstrated in this device.