Topological Hall signal at high magnetic fields in the bulk antiferromagnet Co_0.65Fe_2.35GaTe₂

Fe₃GaTe₂ is claimed to be a two-dimensional intrinsic ferromagnet with a Curie temperature, T_C ~350 K – 380 K. Efforts have been made to modify the magnetic properties of this compound via chemical substitution/doping. Doping or substitution of Fe with Co is found to drastically change the magnetic properties of the material. Here, we report the magnetic and electrical transport properties of the Fe_3-xCo_xGaTe₂ with x ~ 0.2, 0.4, 0.6, 0.7, and 0.8. In our bulk Fe_3-xCo_xGaTe₂ single crystals, the anomalous Hall response reaches values of ρ^A_xy ≅ 48 μΩ cm for Fe_2.3Co_0.7GaTe₂ (T_N ~ 170 K) and ρ^A_xy ≅ 15 μΩ cm for Fe_2.8Co_0.2GaTe₂ (T_C ~ 346 K) respectively. Surprisingly, higher concentrations of Co change the magnetic properties of the parent compound Fe₃GaTe₂ from ferromagnetic to seemingly antiferromagnetic. Lower concentrations of Co doping preserve the ferromagnetic nature of the undoped crystal. For antiferromagnetic Co_0.65Fe_2.35GaTe₂, we found a T_N ~ 170 K but at T = 200 K, we still observe typical ferromagnetic behavior, i.e., hysteresis in the magnetization curves, in contrast to previous reports claiming a phase boundary between paramagnetism and ferromagnetism. If time permits, we will briefly mention neutron diffraction experiments. We also observe a pronounced topological Hall signal which at 1.8 K peaks at a field of 4 T.