Synergistic lattice and carrier modulation through ionic intercalation in 2D ferromagnets

Two-dimensional (2D) van der Waals (vdW) magnets have attracted increasing attention for spintronic applications owing to their intrinsic magnetic order, tunable physical properties, and easy compatibility with heterostructures. Applying these advantages in the practical application, electrical control over the magnetic and electrical properties is essential. However, techniques, such as electrostatic gating, often exhibit limited effectiveness in vdW ferromagnetic metals, as their high intrinsic carrier density screens external electric fields, necessitating impractically high voltages for effective modulation. Alternatively, we herein demonstrate that ionic intercalation provides a fundamentally different control paradigm, enabling synergistic modulation of both carrier concentration and lattice structure throughout the bulk of the vdW ferromagnet Fe3GeTe2. Intercalation of 1-alkyl-3-methylimidazolium ([C2MIm]+) ions into Fe3GeTe2 nanoflakes results in a substantial enhancement of the anomalous Hall resistance (from 0.211 to 1.656 Ω in a champion device). Concurrently, the coercive field decreases by approximately 39%, and the magnetic anisotropy energy is reduced by about 14.8%. First-principles calculations reveal that these adjustments originate from the combined effects of insertion-induced interlayer expansion, decreased carrier concentration, and, most importantly, in-plane lattice distortions. Our findings demonstrate that ionic intercalation enables synergistic tuning of carrier concentration and lattice structure in 2D magnetic materials, providing a versatile route toward next-generation spintronic devices.