Magnetoresistance and the Anisotropic Hybridization Gap in CeNiSn

We have measured the magnetoresistance of the orthorhombic CeNiSn at high fields up to 15 T and at low temperatures down to 0.4 K. The positive magnetoresistance is found to become dominant with the decrease of temperature for the magnetic field H applied along the b- and c-axes in the transverse configuration between the current J and the field H (J ⊥ H). On the other hand, the longitudinal magnetoresistance (J ∥ H) is small in magnitude for H ∥ b and c. For H ∥ a, the magnetoresistance is negative for any current direction. These experimental results have been discussed on the basis of the cyclotron motion of the compensated carriers with closed Fermi surfaces and the reduction of the anisotropic hybridization gap.