Optically Readable Multilevel Magnetic Memory States in Perpendicularly Exchange-Biased Ferromagnetic Multilayers

The construction of multilevel magnetic states using materials with perpendicular magnetic anisotropy (PMA) offers a novel approach to enhancing the storage density and read/write efficiency of nonvolatile magnetic memory devices. In this study, optically readable multilevel magnetic domain states are achieved by inducing asymmetric interlayer interactions and decoupling the magnetic reversal behavior of individual ferromagnetic (FM) layers in exchange-biased FM multilayers with PMA. Hepta-level magnetic domain states are formed in [Co/Pt]_n FM multilayers grown on an antiferromagnetic Fe₂O₃ layer within a relatively low magnetic field range of ∼±400 Oe. Raising and lowering operations between states are demonstrated to be achievable, enabling the writing of new information without the need for initialization in multilevel magnetic memory applications. This design concept, leveraging multilevel magnetic domain states and facilitating noncontact optical reading of stored information, demonstrates the potential to enhance the storage density of nonvolatile magnetic memory devices as it eliminates the need for electrical circuits typically required in other resistive memory technologies.