Metamagnetism and anomalous magnetotransport properties in rare-earth-based polar semimetals RAuGe ($R =$ Dy, Ho, and Gd)

We report the magnetic, magnetoelastic, and magnetotransport properties of single crystals of polar magnets RAuGe ($R=$ Dy, Ho, and Gd), grown by Au-Ge self-flux. Magnetization and magnetostriction measurements reveal multi-step metamagnetic transitions for the c-axis magnetic field (H∥ c) for DyAuGe and HoAuGe, suggesting magnetic frustration in the triangular lattice of R ions. The magnetic phase diagrams have clarified a close connection between the magnetoelastic property and the emergence of the intermediate metamagentic phase. The magnetic-field dependence of the resistivity and Hall resistivity reveal the semimetallic transport dominated by hole-type carriers, consistent with the behavior in a nonmagnetic analogue YAuGe. We also identify a signature of an anomalous Hall effect (AHE) proportional to the field-induced magnetization in $R=$ Dy, Ho, and Gd. GdAuGe shows magnetic and transport behavior as reported in a previous study using Bi-flux grown single crystals, while the self-flux grown crystal shows larger magnetoresistance (~ 345%, at 1.8 K and 9 T) due to higher hole-type carrier mobility (~ 6400 cm²/Vs). Using the two-band model analysis considering the mobility change during the magnetization process, we extract the anomalous Hall conductivity: ~ 1200 S/cm and ~ 530 S/cm for $R=$ Dy and Ho, respectively, at 1.8 K with 9 T for H∥ c. The magnitude of conductivity suggests a contribution of intrinsic origin, possibly related to the Berry curvature in the electron bands induced by the time-reversal symmetry breaking and the polar lattice.