Topological Hall Effect in Antiferromagnetic Co-Doped Fe₃GaTe₂

Fe₃GaTe₂ is a van der Waals (vdW) ferromagnet with a Curie temperature T_C ranging from 350 to 380 K, followed upon cooling by a ferrimagnetic transition near room temperature. Substituting Fe with Co was previously reported to induce antiferromagnetism (AFM) at a Co fraction-dependent Néel temperature T_N. In this work, we confirm the overall phase diagram of the Fe_3-xCo_xGaTe₂ series as a function of x and temperature via magnetization and electrical transport measurements. For x ⩾ 0.6, the Hall effect is observed to mimic the magnetization as the AF ground state is suppressed by the external magnetic field via a metamagnetic transition, thus displaying an anomalous Hall response. At low temperatures, we also observe a pronounced topological Hall signal peaking at μ₀H = 4 T, or within the metamagnetic transition region of fields. This observation points to the presence of magnetic field-induced chiral spin textures, such as skyrmions, upon approaching magnetization saturation. Magnetic force microscopy (MFM) reveals the emergence of nearly circular magnetic domains, with diameters on the order of 100-200 nm, within the antiferromagnetic phase. A detailed analysis of the MFM images indicates that the topological Hall effect is closely linked to the field-induced stabilization of magnetic domain structures, likely exhibiting chiral textures. This observation suggests the possible formation of skyrmions already in the AFM phase, i.e., AFM skyrmions, that evolve into ferromagnetic (FM) ones upon increasing the magnetic field. Consequently, Co-doped Fe₃GaTe₂ might provide a platform to investigate the transformation of skyrmions, initially coupled antiferromagnetically into ferromagnetic ones, and to explore its impact on the topological and skyrmion Hall effects.