Anomalous Hall effect and magnetic structure of the topological semimetal (Mn0.78Fe0.22)3Ge

Me3+8Ge, being a Weyl semimetal, shows a large anomalous Hall effect (AHE), which decreases slowly with an increase in 8 from 0.1 to 0.4. However, AHE in this compound remains significantly large in the whole range of 8 because of the robust nature of the topology of bands. To explore the possibility of tuning the anomalous transport effects in Weyl semimetals, we have studied the single-crystal hexagonal-(Mn0.78Fe0.22)3Ge compound. Magnetization of this compound shows two magnetic transitions at 242 K (TN1) and 120 K (TN2). We observed that the AHE persists between TN2-TN1 and vanishes below TN2. Further, we performed single-crystal neutron diffraction experiments (using spherical neutron polarimetry and unpolarized neutron diffraction) to determine the magnetic structures of (Mn0.78Fe0.22)3Ge at different temperatures. Our neutron diffraction results show that the sample possesses a collinear antiferromagnetic structure below TN2. However, the magnetic structure of the sample remains noncollinear antiferromagnetic, the same as Mn3Ge, between TN1 to TN2. The presence of AHE, and noncollinear magnetic structure in (Mn0.78Fe0.22)3Ge, between TN1 and TN2, suggest the existence of Weyl points in this temperature regime. Below TN2, AHE is absent, and the magnetic structure also changes to a collinear antiferromagnetic structure. These observations signify a strong link between the magnetic structure of the sample and AHE.