Revealing a large temperature dependence of the Hall effect in the “non-metallic” metal FeCrAs

The system FeCrAs presents a curious duality in its behaviour: its resistivity is in the metallic range, but with a non-metallic temperature dependence from above 800 K to below 100 mK. Furthermore, a distorted Kagomé lattice magnetically frustrates Cr moments, which causes magnetic fluctuations that survive far beyond the antiferromagnetic ordering temperature of T_N ~ 125 K. Considering the strong anomaly in resistivity at T_N, along with a non-metallic temperature dependence extending beyond 800 K, it is natural to postulate that the exotic scattering of electrons is closely tied to its magnetic fluctuations.
Here, we report the temperature dependence of the classical Hall effect in FeCrAs. It is typically used to study the carrier density of a material, but it can also be used to investigate the scattering rate. We observe that there is a strong temperature dependence in the low-field Hall coefficient, R_H. In particular, there is an anomaly when FeCrAs is near T_N, and below this, there is a sign-reversal in R_H when the field directed along the c-axis. This suggests that there is a strong relationship between the spin degree of freedom and the electronic scattering that is not captured by theoretical treatments.