Giant coercivity enhancement in a room-temperature van der Waals magnet through substitutional metal-doping

FeGeTe₂ (x = 3, 4, and 5) systems, two-dimensional (2D) van der Waals (vdW) ferromagnetic (FM) metals with high Curie temperatures (T_C), have been intensively studied to realize all-2D spintronic devices. Recently, an intrinsic FM material Fe₃GaTe₂ with high T_C (350-380 K) has been reported. As substitutional doping changes the magnetic properties of vdW magnets, it can be a powerful means for engineering the properties of magnetic materials. Here, the coercive field (H_c) is substantially enhanced by substituting Ni for Fe in (Fe_1-Ni)₃GaTe₂ crystals. The introduction of a Ni dopant with x = 0.03 can enhance the value of H_c up to ∼200% while maintaining the FM state at room temperature. As the doping level increases, T_C decreases, whereas H_c increases up to 7 kOe at x = 0.12, which is the highest H_c reported so far. The FM characteristic is almost suppressed at x = 0.68 and a spin glass state appears. The enhancement of H_c resulting from Ni doping can be attributed to domain pinning induced by substitutional Ni atoms, as evidenced by the decrease in magnetic anisotropy energy in the crystals upon Ni doping. Our findings provide a highly effective way to control the H_c of the 2D vdW FM metal Fe₃GaTe₂ for the realization of Fe₃GaTe₂ based room-temperature operating spintronic devices.