Epitaxial Growth of 2D Single-Crystal Spinel Oxide with High-Entropy Driven Magnetic Homogenization.

2D high-entropy oxides (HEOs) are an emerging class of entropy-stabilized materials with unique mechanical, catalytic, and magnetic properties distinct from their bulk counterparts. However, the influence of disordered multivalent cations with varying spin orientations on magnetic exchange interactions remains unexplored due to challenges in synthesizing atomically thin HEOs. Here, the van der Waals epitaxial growth of 2D single-crystalline spinel-typed high-entropy (CoCrFeMnNi)3O4 nanoflakes with a thickness down to two unit cells via a molecular sieve-assisted chemical vapor deposition method is reported. The addition of molecular sieves enables a steady vapor supply and assists in achieving a more uniform cation distribution, confirmed by atomic-resolution STEM imaging. Compared to 2D Fe3O4 reference nanoflakes, these HEOs provide a robust platform to study entropy-driven magnetic behavior in nonlayered 2D spinels. The HEO nanoflakes preserve long-range ferrimagnetic order and exhibit isotropic saturated magnetization and coercivity. Magnetic force microscopy reveals domain evolution from single-domain to vortex, and ultimately to multidomain states with well-defined and straight domain walls depending on nanoflake size and thickness. These findings verify magnetic homogenization and a gradually harder magnetic transition arising from randomly distributed cations with competing interactions, demonstrating the potential of high-entropy design in tailoring magnetic properties of 2D oxides.