Magnetoresistance of yttrium alloys with dilute rare-earth solutes.

Abstract

The magnetoresistance (MR) of some yttrium--rare-earth alloys has been investigated in the liquid-helium temperature range in magnetic fields up to 30 kOe. A negative MR is observed for the ``Kondo'' alloy, Y-Ce(3 at %), which is consistent with theory based on isotropic conduction-electron--f-electron scattering between the conduction electron and the magnetic ion. In the paramagnetic phase the spin-glass alloy, Y-Dy(2 at. %), shows a negative MR at low fields but at higher fields and temperatures the MR becomes positive. The positive MR is thought to be associated with ``normal magnetoresistance'' due to the Lorentz force. A contribution due to anisotropic k-f scattering is also expected in the MR data. The MR of antiferromagnetic Y-Tb(3 at. %) is positive and increases with field up to ${H}_{c}$\ensuremath{\simeq}12 kOe at 4.2 K. For T${T}_{N}$ (${T}_{N}$=5.2 K), the positive MR is interpreted to be the result of field-induced enhancement of the spin fluctuations. The MR is negative for T>${T}_{N}$ H>${H}_{c}$ as expected in the paramagnetic phase. The longitudinal and transverse magnetoresistances are not equal. It is believed that this anisotropy arises from an anisotropic scattering between the conduction electrons and the f electrons. The sign of the anisotropy is found to be consistent with the present theory.