Helimagnet-based Non-volatile Multi-bit Memory

Existing semiconductor-based memory devices suffer from high power, low density, and lack of multi-bit capability. To overcome these limitations, emerging memory technologies based on spatially varying spin textures, such as helimagnets and skyrmions, are promising. In this work, we propose a helimagnet-based memory that can store multi-bits of information. The memory device consists of a helimagnet layer sandwiched between two ferromagnetic layers that are used to lock the spin configurations. The bottom pinned layer consists of large anisotropy energy that can fix the bottom layer spin configuration to a set axis, and the top free layer can rotate under applied in-plane fields. We first find the relaxed spin structure, resulting from competition between DMI and exchange energy, and it is defined as an equilibrium state (“0”). The writing of a memory state is simulated by using an in-plane field that will rotate and transform the spin configurations of the memory device. Our results show that stable configurations can be at rotations of an integer multiple of 180 degrees (corresponding to states “-2”, “-1”, “1”, “2”, etc.), where anisotropy stabilizes the free layer. An intermediate unstable spin configuration tends to revert to its adjacent state. Simply by changing the field in a different direction, i.e., toggle switching, we could achieve multi-bit data storage per unit memory cell.