Hall effect in NdB$_6$

We report results of electrical resistivity, Hall effect and magnetization measurements in a NdB$_6$ single crystal, in a temperature range from 2 to 300 K and in magnetic fields of up to 7 T. We took care to use low magnetic fields ($H_{appl} < 1$ T) in our Hall effect experiments in order to avoid magnetic field smearing out anomalies at the critical points. The Hall resistivity $\rho_H$, which is electronlike, shows a maximum at $T\simeq T_N$. In the paramagnetic (PM) region, we find a linear dependence of $\rho_H/H_{appl}$ on effective susceptibility. This enables us to separate two contributions to the Hall effect, an ordinary and an anomalous one. The estimated anomalous Hall coefficient $R_s$ (holelike) is much larger than the ordinary one in the PM state and is independent of temperature. As the antiferromagnetic (AF) order sets in below $\sim 8$ K, $R_s$ decreases sharply with decreasing temperature. In the AF state, $R_s\propto\rho$, where $\rho$ is the total resistivity. We do not find any significant variations of the anomalous Hall coefficient near the critical point. Both magnetization and Hall voltage show an amomaly in low magnetic fields, which may be related to domain rotations.