Room-temperature nonlinear Hall effect in symmetry-engineered van der Waals ferromagnetic (Fe0.74Co0.26)3GeTe2 nanodevices

The second-order nonlinear Hall effect (NLHE), the leading Hall-like response beyond the linear regime, has attracted broad interest as a probe of symmetry breaking and band-geometry-related transport, with potential applications in low-power electronics. However, its realization in van der Waals (vdW) magnets remains fundamentally constrained by the prevalent inversion symmetry of these materials, which forbids a finite second-order Hall conductivity. Here, we realize a robust second-order NLHE up to room temperature in the chemically engineered vdW ferromagnet (Fe0.74Co0.26)3GeTe2. Polarization-resolved second-harmonic generation confirms doping-induced inversion-symmetry breaking, and nonlinear transport measurements reveal a clear quadratic Hall response with a finite second-order Hall conductivity at 300 K. Combined scaling and symmetry analyses suggest an important role of scattering-related mechanisms in the observed NLHE. These findings establish chemically engineered vdW magnets as a promising platform for room-temperature nonlinear transport and nonlinear spintronic functionalities.