Emerging 2D Ferromagnetism in Graphenized GdAlSi

Abstract 2D magnets are expected to give new insights into the fundamentals of magnetism, host novel quantum phases, and foster development of ultra‐compact spintronics. However, the scarcity of 2D magnets often makes a bottleneck in the research efforts, prompting the search for new magnetic systems and synthetic routes. Here, an unconventional approach is adopted to the problem, graphenization – stabilization of layered honeycomb materials in the 2D limit. Tetragonal GdAlSi, stable in the bulk, in ultrathin films gives way to its layered counterpart – graphene‐like anionic AlSi layers coupled to Gd cations. A series of inch‐scale films of layered GdAlSi on silicon is synthesized, down to a single monolayer, by molecular beam epitaxy. Graphenization induces an easy‐plane ferromagnetic order in GdAlSi. The magnetism is controlled by low magnetic fields, revealing its 2D nature. Remarkably, it exhibits a non‐monotonic evolution with the number of monolayers. The results provide a fresh platform for research on 2D magnets by design.