We report Hall, magnetic, heat capacity and doping studies from single crystals of Yb14MnSb11 and Yb13.3La0.7MnSb11. These heavily doped semiconducting compounds are ferromagnetic below 53 K and 39 K respectively. The renormalization of the carrier mass from 2me near room temperature to 15me at 5 K , plus the magnetic evidence for partial screening of the Mn magnetic moments suggest that these compounds represent rare examples of an underscreened Kondo lattice with TK ≈ 350 K.
We present results of time-of-flight inelastic neutron scattering phonon density of states measurements on ͑La, Ce͒ 0.9 Fe 4 Sb 12 and CoSb 3 as well as of a detailed comparison with lattice dynamical models in the literature. The MARI experimental setup is replicated by a theory for scattering from a polycrystalline material. The model considered for the filled materials is a local density approximation ͑LDA͒ based short-range force constant model and those considered for CoSb 3 are the LDA-based model with the La-related parameters removed and a semiempirical model. We show that the presence of La significantly affects the shape of the spectrum. We also conclude that upon filling the Sb intrasquare force constants are weakened and that the transition-metal Sb bonds are almost unchanged.
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