Two-dimensional (2D) van der Waals (vdW) ferromagnet ${\text{Fe}}_5{\text{GeTe}}_2$ (F5GeT2) is a promising candidate for spintronic applications due to its intrinsic near-room-temperature ferromagnetism, magnetic anisotropy, excellent tunability, and emergent topological magnetic textures. However, the delicate ferromagnetic order and moderate magnetic anisotropy hinder its practical implementation in next-generation spin-based devices. Doping with specific elements has been demonstrated to be an effective strategy for enhancing ferromagnetism and elevating the Curie temperature ($T_C$) in such systems. In this work, we synthesized lightly Ni-doped $({\text{Fe}}_{5-x}{\text{Ni}}_x{)}_5{\text{GeTe}}_2({\text{Ni}}_x\text{−}\mathrm{F}5\text{GeT}2)$ single crystals and conducted a comprehensive investigation into their magnetic properties. We found that even a small amount of Ni-doping can significantly elevate $T_C$ and enhance the easy in-plane anisotropy (EPA) compared with pristine F5GeT2. By employing the modified Arrott plot (MAP) method and critical isotherm (CI) analysis, the critical exponents for two distinct magnetic field orientations are obtained. For ${\text{Ni}}_{0.05}\text{−}\mathrm{F}5\text{GeT}2$, we determine $\beta =0.385(7)$, $\gamma =1.303(4)$, and $\delta =4.696(5)$ for $H//ab$, and $\beta =0.359(1)$, $\gamma =1.195(7)$, and $\delta =4.455(1)$ for $H//c$. For ${\text{Ni}}_{0.1}\text{−}\mathrm{F}5\text{GeT}2)$, we find $\beta =0.354(9)$, $\gamma =1.342(5)$, and $\delta =4.764(6)$ for $H//ab$, and $\beta =0.368(2)$, $\gamma =1.242(1)$, and $\delta =4.561(1)$ for $H//c$. These derived exponents exhibit excellent self-consistency and adhere to the Widom scaling relation. However, the critical exponents do not conform to any single theoretical universality class, which indicates the presence of anisotropic magnetic exchanges induced by the Ni-doping. The magnetic interactions of ${\text{Ni}}_{0.05}\text{−}\mathrm{F}5\text{GeT}2$ and ${\text{Ni}}_{0.1}\text{−}\mathrm{F}5\text{GeT}2$ fall between the short-range and long-range limits, suggesting that low-concentration Ni-doping modulates the spin decay distances of the system. Our findings establish a pathway for tailoring the magnetic properties of 2D-vdW ferromagnets through doping engineering, expanding the prospects for developing high-performance room-temperature spintronic devices.

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• Magnetic anisotropy
• Magnetic texture
• Magnetization dynamics
• Spintronics
• Ferromagnets
• Magnetic semiconductors
• van der Waals systems
• Crystal growth