Nature of half-metallic ferromagnets: Transport studies

Abstract

The half-metallic ferromagnetic compounds due to the absence of states at EF for minority spin electrons, as predicted by band theory, should exhibit unique features in their transport properties. Transport measurements conducted as a function of T and H for NiMnSb and PtMnSb thin films show interesting behavior. In H=0, the resistivity versus T shows the absence of the T2 dependence at low temperature found in ferromagnets such as Fe, Ni, etc. The Hall constant increases significantly below about 100 K for both compounds; NiMnSb shows a factor of seven increase. Transverse magnetoresistance changes sign between 295 and 4.2 K. Transport data seem to imply a drop in the carrier density and a large increase in their mobility at low temperatures, which is consistent with zero density of states for minority spins at EF, but additional measurements are needed to clarify theoretical understanding.