Li-ion intercalation-driven control of two-dimensional magnetism in van der Waals FePS bilayers.

Manipulating two-dimensional (2D) magnetism in layered van der Waals (vdW) materials like FePS (FPS), with its wide-ranging applications in flexible spintronic devices, poses a persistent challenge. Through first-principles calculations, we have achieved reversible ferrimagnetic (FiM, FePS bilayer) ↔ antiferromagnetic (AFM, 1Li-intercalated FePS bilayer) ↔ ferromagnetic (FM, 2Li-intercalated FePS bilayer) phase transitions by using a Li-ion intercalation method. Intercalated Li ions significantly enhance the Fe-3d and S-3p hybridization and reduce the Fe-Fe, Li-Fe, Li-S, and Li-P bond lengths. The manipulation of 2D magnetism in Li-intercalated FPS bilayers can be attributed to the charge transfer between two FPS monolayers mediated by Li ions. Moreover, this study offers insights into the underlying physical mechanisms that govern the variations of electronic structures, 2D magnetism, magnetic anisotropy energy, and exchange couplings. Our reversible Li-ion intercalation permits straightforward de-intercalation using a two-step route, thereby reinstating the initial magnetic order of the FPS bilayer. Our purpose-designed FPS bilayer with different Li concentrations and robust exchange coupling not only enriches the Li-intercalation physics in the FPS system but also offers a general pathway for manipulating 2D magnetism in Fe-based vdW trisulfides.