Increase conductivity in UNiSn with the application of magnetic fields

We report on the frequency dependent conductivity of the modified Huesler alloy UNiSn in the antiferromagnetic state and in the presence of a magnetic field. UNiSn is paramagnetic above 43 K and has a semiconducting gap of about 65 meV. Below 43 K, the compound is in an itinerant antiferromagnetic state. The reflectance of UNiSn is measured from 4 meV to 0.4 eV and in fields up to 16 Tesla. At 5 K, there is a shift in spectral weight from the gap region to lower frequencies as the applied magnetic field is increased. This shift in spectral weight gives rise to increase conductivity with applied field in the metallic state. However, the gap value is unaffected by the field. No field dependence is observed for the isostructural compound, ThNiSn, which does not undergo an antiferromagnetic transition.