Magnetic property of directly exfoliated and dispersed Fe₃GeTe₂ and Fe₅GeTe­₂ in pure water

Fe_xGeTe₂ (X=3, 5), two-dimensional(2D) ferromagnetic materials, have attracted many researchers due to its strong Ising-type anisotropy and relatively high curie temperature. However, methods for preparing large-area Fe_xGeTe₂ film is at a starting point. Selection of precursors and optimization of synthesis condition make overall progress and design of experiment complicated, as they are composed of three elements. Here, we exfoliate Fe₃GeTe₂ and Fe₅GeTe₂ via wet exfoliation in pure water by sonication with heating and fabricate cm-scale film through filtration. The coercivity of Fe_XGeTe₂ film increases dramatically, in the case of Fe₃GeTe₂, from 20mT which is coercivity of bulk crystal, to 650mT. The coercivity of Fe_XGeTe₂ is reported to increase as their thickness decreases. When they become thinner, they behave as single-domain magnet, so that their coercivity increases. Even when they are stacked in film form, edge-functionalization disturbs interactions between nano-magnets, situation doesn’t change. Our work suggests a simple and facile method to fabricate large-area film of Fe_xGeTe₂ with improved magnetic properties.