Multivalued Memory via Freezing of Super-Hard Magnetic Domains in a Quasi 2D-Magnet

The design of high-density non-volatile memories is a long-standing dream, limited by conventional storage "0" or "1" bits. An alternative paradigm exists in which regions within candidate materials can be magnetized to intermediate values between the saturation limits. In principle, this paves the way to multivalued bits, vastly increasing storage density. Single-molecule magnets, are good examples offering transitions between intramolecular quantum levels, but require ultra-low temperatures and limited relaxation time between magnetization states. It is showed here that the quasi 2D-Ising compound BaFe₂ (PO₄ )₂ overcomes these limitations. The combination of giant magneto-crystalline anisotropy, strong ferromagnetic exchange, and strong intrinsic pinning creates remarkably narrow magnetic domain walls, collectively freezing under T_f ≈15 K. This results in a transition from a soft to a super-hard magnet (coercive force > 14 T). Any magnetization can then be printed and robustly protected from external fields with an energy barrier >9T at 2 K.