NMR and Magnetic Study of Half-Heusler Semiconductor NbFeSb

The Half-Heusler semiconductor NbFeSb has been of considerable interest due to its excellent thermoelectric performance, especially its enhanced power factor.^[1] To further investigate the electronic properties of these materials, we have done ⁹³Nb NMR and magnetic measurements on several NbFeSb samples with different defect densities, prepared at a series of hot pressing temperatures. Magnetization measurements show the presence of paramagnetic defects in undoped samples with a concentration of about 0.002 per formula unit independent of processing. MAS NMR measurements yield narrow lines with almost identical shifts of +3600 ppm. Changes in static-NMR line widths and amplitudes indicate a significantly larger concentration of apparently electrically inactive defects for samples prepared at lower processing temperatures. In addition, the NMR T₁ relaxation time measurements vs. temperature indicate a wide distribution of local behavior which we have analyzed in terms of the distribution of magnetic defects in these samples. [1] He et al., Proc. Natl. Acad. Sci. U. S. A. 113, 13576-13581 (2016).