Impurity and magnetic field investigation of PrOs$_{4}$Sb$_{12}$

\\ We have performed a low level doping study of PrOs$_{4}$Sb$_{12}$. Samples with small amounts of La and Nd substituted for Pr were investigated by magnetic susceptibility and specific heat in magnetic fields to 14 T. The goal of this study was to search for correlations between superconductivity, effective electron mass, crystalline electric fields, and field-induced antiferro-quadropolar order. In agreement with our previous study $^{1}$, we find T$_{c}$ to be only weakly affected by the alloying while other characteristics, such as the specific heat discontinuity at T$_{c}$ and the width of the transition, show a dramatic dependence on the concentration of impurities. Results will be discussed in relation to considered models of superconductivity and heavy fermion behavior. Supported by Department of Energy, grant No. DE-FG02-99ER45748. \\ \\ $^{1}$ C. R. Rotundu, P. Kumar, B. Andraka, cond-mat/0402599