Exotic magnetic and transport properties of type-II Weyl semimetal NdAlGe

Abstract

Weyl semimetals, influenced by both time-reversal symmetry (TRS) and inversion symmetries (IS), are relatively rare and offer an excellent platform for exploring the connection between chiral currents and magnetic ordering. The NdAlGe compound, grown in a single crystalline form through the flux method, possesses a noncentrosymmetric I41md crystal structure, breaking inversion symmetry. Its magnetic susceptibility exhibits anisotropic behavior. It shows ferromagnetism when the magnetic field is applied parallel to the c-axis (H‖c). An antiferromagnetic transition occurs for the other case(H⊥c). Additionally, the ferromagnetism of NdAlGe undergoes a metamagnetic transition, resulting in an increase in the magnetic moment from 0.9 μB/f.u. to 2.7 μB/f.u.. This leads to a high magnetocaloric effect and enables magnetic refrigeration of hydrogen. Band structure calculations have revealed that NdAlGe belongs to the category of type-II Weyl semimetals, hosting 40 Weyl nodes in the ab-plane, along with a likely Fermi surface nesting vector. The ferromagnetic spin alignment contributes significantly to an anomalous Hall coefficient (R_S) and a large anomalous Hall conductivity. The constant for the large anomalous Hall conductivity was found to be directly proportional to magnetization at a magnetic field of 50 kOe. The large anomalous Hall effect comes from the Karplus and Luttinger (KL) analysis, indicating that the AHE is linked to the intrinsic Berry curvature within the NdAlGe compound. This intrinsic Berry curvature is further confirmed through the planar Hall effect over a wide temperature range, suggesting that the Weyl semimetallic properties are not strongly dependent on the magnetic order.