Antiferromagnetic order and 4f-instability of CePb3

We have measured the static magnetic susceptibility of CePb₃ and LaPb₃ between 0.5 and 1,000 K and 1.5 and 900 K, respectively and the specific heat of CePb₃ between 1.5 and 40 K. The data show clearly an antiferromagnetic phase transition at 1.25 K. The order occurs in a doublet 4f groundstate whose entropy is removed only partially by long range order. There are strong indications for quadrupole-quadrupole interactions enhancing the ordering energy over that from spin spin interactions alone. The CEF splittings seem to depend on temperature. The 4f-instability in CePb₃ is quite weak.