The realization of long-range spin order in two dimensions (2D) has catapulted the search for layered materials with magnetic ordering above room temperature. These efforts aim to understand and enhance the spin–spin interactions in 2D. An emergent class of such magnets is the layered ${\mathrm{Fe}}_N{\mathrm{GeTe}}_2$ (N $=3$, 4, and 5). Here, we investigate the magnetic states over a wide field–temperature phase space in the high-$T_{\mathrm{c}}$ ferromagnet ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ using magnetization, ferromagnetic resonance (FMR), and magnetotransport measurements. Our findings reveal a magnetic phase transition from a collinear to a complex noncollinear magnetic order near the temperature $T^{*}\approx 160$ K, below which magnetic susceptibility is reduced, FMR linewidth broadened, and anomalous Hall resistivity suppressed. Such noncollinearity results from the competition between magnetocrystalline anisotropy and Dzyaloshinskii–Moriya interaction arising from the unusual Fe1 ordering in two possible split sites. Our study focuses on the strategy to quench the noncollinear spin order. Substituting 40% Ni in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ is found to be one such quenching strategy. This provides deeper insights into the magnetism of a high-$T_{\mathrm{c}}$ layered ferromagnet, offering opportunities to develop 2D magnet-based devices.

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• Electrical properties
• Hall effect
• Magnetic anisotropy
• Magnetic phase transitions
• Magnetism
• Magnetization dynamics
• Magnetotransport
• 2-dimensional systems
• Layered crystals
• Ferromagnetic resonance
• Magnetization measurements