The effect of Nd substitution on superconductivity of PrOs$_4$Sb$_{12}$

The filled skutterudite compound PrOs$_4$Sb$_{12}$ is an unconventional heavy fermion superconductor with $T_c$=1.85K. Our recent study shows that NdOs$_4$Sb$_{12}$ is a heavy fermion ferromagnet ($T_{FM}\sim$1K) with possible spin wave excitations. Previous experimental evidence suggests that the superconducting pairing in PrOs$_4$Sb$_{12}$ is spin-triplet, which, when considered along with the low $T_{FM}$ of NdOs$_4$Sb$_{12}$ implies that PrOs$_4$Sb$_{12}$ may be near a ferromagnetic quantum critical point. We have measured zero-field ac magnetic susceptibility and electrical resistivity between 0T and 8T for the (Pr$_{1-x}$Nd$_x$)Os$_4$Sb$_{12}$ system with $x$=0.1, 0.2, 0.4, 0.6, 0.8. The superconductivity persists to $x$=0.4 and the ferromagnetism appears above $x$=0.6. In the normal state of samples with x=0.1, 0.2, 0.4, the features related to the antiferroquadrupolar phase are clearly observed, in contrast to the disappearance of the features above x=0.05 in the Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ system. The phase diagrams of $T_{c}$ and $T_{FM}$-Nd concentration $x$ and $H$-$T$ will be presented. Funded by U.S. DOE and NSF; NHMFL by NSF, FL, and DOE.