Transport and magnetic properties of the topological (Weyl) semimetal: Hexagonal - (Mn_1-αFe_α)₃Ge (α = 0 – 0.3)

In the case of Mn₃Ge, the anomalous Hall effect (AHE) has its origins in the topological Weyl nodes. The AHE can be controlled by tuning of the Weyl points relative to the Fermi surface, by suitable dopants of the parent phase. Therefore, we have explored the electrical transport and magnetic properties of the single crystal (Mn_1-αFe_α)₃Ge to study the change in AHE and chiral anomaly with Fe doping. Clear signatures of the AHE and chiral anomaly were observed for samples up to α = 0.22, in the temperature regime where magnetization behaves the same as the parent sample. However, the strength of AHE and chiral anomaly decreases with an increase in Fe doping and vanishes beyond α = 0.22. To predict the origin of AHE in doped samples, the ground state magnetic structure of α = 0.22 was determined using single-crystal (polarized and unpolarized) neutron diffraction techniques. We observed that the magnetic structure of the doped sample remains the same as that of the parent compound in the temperature regime where AHE was observed. These observations led us to two main conclusions: (i) the Weyl points are very likely to be present in the doped samples, and (ii) the characteristics of the Weyl points can be tuned significantly by suitable doping of the Weyl semimetals.