NMR investigation of the skutterudite compound Co Sb3

We report the results of a Co59 nuclear magnetic resonance (NMR) study of the skutterudite compound Co Sb3. The absence of associated NMR line broadening with temperature indicates the material to be intrinsically nonmagnetic. The isotropic Knight shift and NMR relaxation rate go over to a thermally activated response, indicative of semiconducting behavior. The extracted energy gap of about 40 meV is found to be in good agreement with the results obtained from the band structure calculations. In addition, the observed exotic features are associated with the s -character carriers thermally across the band edges. Analysis using the Korringa relationship for an intrinsic semiconductor yields a lighter hole mass, being consistent with the p -type transport property in Co Sb3.