Kondo-holes in La-doped CeOs$_{4}$Sb$_{12}$

CeOs$_{4}$Sb$_{12}$ is an example of an interesting class of systems with low carrier concentrations in which strongly electron correlated states develop at low temperatures. 2{\%} of La introduced for Ce suppresses the 1.1 K ordering and leads to exotic heavy fermion behavior. Electrical resistivity of weakly La-doped alloys, studied down to 20 mK, is proportional to the square of temperature, but with the proportionally coefficient (A) being negative. Such a temperature variation is characteristic of Kondo-hole systems. The absolute value of A (-45 $\mu \Omega $cm/K$^{2}$ for Ce$_{0.98}$La$_{0.02}$Os$_{4}$Sb$_{12})$ implies presence of massive quasiparticles. Magnetic fields reduce the absolute value of A and, for sufficiently strong fields, lead to a Fermi-liquid temperature variation (positive A).