Hall effect in PrB${}_6$ and NdB${}_6$

Abstract

Hall effect was studied on the single crystals of antiferromagnets PrB${}_6$ and NdB${}_6$ at temperatures 2K$<$T$<300$K in magnetic fields up to 8T using the sample rotation technique. At low magnetic fields ${\mu }_0$H$\le 1$T Hall coefficient R${}_{\mathrm{H}}$, which is practically temperature independent in paramagnetic state at 8K$\le$T$\le 70$K, is characterized by the values of R${}_H$(PrB${}_6$)$\sim -(4.2\pm 0.1)\cdot 10^{-4}$ cm${}^3$/C and R${}_H$(NdB${}_6$)$\sim -(4.1\pm 0.1)\cdot 10^{-4}$ cm${}^3$/C. Rather different behaviour of R${}_H$ is observed in antiferromagnetic (AF) phases of these hexaborides. For PrB${}_6$ the decrease of temperature below T${}_N\approx 6.7$K is accompanied by a noticeable ($\Delta R_H/R_H\sim 10$) elevation of R${}_H$(${\mu }_0$H$=1$T) to the values of $-(3.8\pm 0.1)\cdot 10^{-4}$ cm${}^3$/C. On the contrary, the low field Hall coefficient in NdB${}_6$ diminishes by about 15% reaching the value R${}_H\approx -(4.7\pm 0.1)\cdot 10^{-4}$ cm${}^3$/C in AF state at 2.5K. The increase of magnetic field inducing magnetic transition in the commensurate magnetic phase of PrB${}_6$ results in essential R${}_H$ changes (up to 10%) at liquid helium temperatures. The anomalous behaviour of the charge transport parameters for RB${}_6$ (R=Pr, Nd) found in vicinity of Neel temperature suggests the possible effect of $5d$-states spin density polarization of both in AF and paramagnetic states of the compounds under investigation.

17 pages,7 figures