Multi-Level Switching and Reversible Current Driven Domain-Wall Motion in Single CoFeB/MgO/CoFeB-Based Perpendicular Magnetic Tunnel Junctions

One of the critical issues in spintronics-based technologies is to increase the data storage density. Current strategy is based on shrinking the devices size down to tens of nanometers, or several nanometers, which is reaching its limit. A new proposal is to use multi-level cells (MLCs) to store more than two bits in each cell. In this work, the multi-level switching is realized in CoFeB/MgO/CoFeB based nano-scale single perpendicular magnetic tunnel junctions (p-MTJs) with three or four stable resistance states. A large range of writing currents for each state is obtained, accompanying with a good repeatability of set-reset operations between different states. The developed multi-domain model perfectly matches the experimental results, reflecting the magnetic behaviors during multi-level switching. Furthermore, current-driven domain wall (DW) motion is revealed in the circular p-MTJs, where the DW position can be reversibly manipulated by applied current. To design high-performance multi-level p-MTJs, the parameter diagrams are calculated, suggesting various feasible strategies to improve the multi-level switching through materials optimization and devices geometry. In summary, the demonstration of multi-level switching in single p-MTJ shows the high potential of realizing the new generation of p-MTJ-based multi-level spintronic devices, such as multi-level memories and spin-neuron devices.