Unlocking the charge doping effect in softly intercalated ultrathin ferromagnetic superlattice

Abstract

The electrolyte-assisted exfoliation strategy is widely employed to synthesize ultrathin two-dimensional (2D) materials. Yet, spins in 2D magnets are susceptible to the electrolyte due to the underlying charge doping effect. Hence, it is crucial to understand and trace the doping process during the delamination of 2D magnets. Taking the prototype Fe₃GeTe₂, we utilized soft organic cations to exfoliate the bulk and obtain a freestanding organic–inorganic hybrid superlattice with a giant electron doping effect as high as 6.9 ​× ​10¹⁴/cm² (∼1.15 electrons per formula unit). A remarkable ferromagnetic transition exceeding 385 ​K was revealed in these superlattices, together with unique anisotropic saturation magnetization. The doping enhanced the in-plane electron–phonon coupling and thus optimized originally poor indirect double-exchange scenario for spin electrons. The emerging vertical magnetization shift phenomenon served to evaluate the uniformity of charge doping. The above findings provide a new perspective for understanding the role of parasitic charge in 2D magnetism.