Annealing effect on the reduction of Fermi-level density of states in CoTiSb: NMR evidence

With the aim to examine the variation in the electronic properties of CoTiSb due to heat treatment, a comparative study of the as-cast and annealed samples using Co-59 nuclear magnetic resonance (NMR) spectroscopy was performed. All NMR observations clearly indicate a significant change in the local electronic characteristics for the annealed sample. The spin-lattice relaxation rate measurements further provide an estimate of Co-d Fermi-level density of states, N-d(E-F), indicating a substantial reduction in N-d(E-F) for the specimen with heat treatment. This finding gives a microscopic interpretation for the larger electrical resistivity and Seebeck coefficient in the annealed half-Heusler alloys, as the samples with higher electrical resistivity and Seebeck coefficient usually are associated with lower carrier densities in the vicinity of the Fermi level.