Multi-Bit Magnetic Memory Based on Magnetic Multilayer Pillars With a Two-Terminal Structure

Vertical nanopillars are ideal building blocks for magnetic memory devices because of their thermal stability and scalability, rendering them suitable for high-density, nonvolatile storage. Multi-bit magnetic memory using such structures often relies on domain wall motion in multilayer configurations. However, attaining dependable multi-bit operation remains a formidable challenge, particularly in regulating magnetization at the pillar base. In this study, we use micromagnetic simulations to investigate magnetization control in a magnetic multilayer pillar on an in-plane magnetized layer. The pillar comprises alternating layers with and without perpendicular magnetic anisotropy. When the bottom layer of the pillar lacks perpendicular anisotropy, spin injection from the in-plane magnetized layer and spin-polarized current flowing through the pillar reverse the magnetization at the pillar base. This process results in the formation of a new domain and an accompanying domain wall, generating a new bit pattern. The domain wall moves with the current, and its motion can be modulated using pulse or constant currents that suppress magnetization reversal. By precisely adjusting the timing of these current applications, multiple stable magnetic states corresponding to various bit patterns can be realized within the pillar. This approach could significantly enhance data density and energy efficiency in next-generation nonvolatile memory technologies.