COEXISTENCE OF MAGNETIC AND NON MAGNETIC STATES IN CE(14)X(51) (X=AU,AG AND CU)

Magnetic (chi), thermal(C-p), and transport (p) measurements on Ce(l4) X(51) (X = Au, Ag and Cu) are presented. All these compounds show anti ferromagnetic type order at low temperatures, with T-N = 0.9 K (Au), 1 .1 K (Ag) and 3.2 K (Cu). Within the Gd14Ag51-type structure the Ce at oms sit in different sublattices denoted by I (2 atoms), II (6 atoms) and III (6 atoms), therefore the results can be interpreted in terms o f three different behaviors of Ce depending on its local environment. From the entropy involved in the magnetically ordered (MO) phase it ca n be established that the Ce-II and Ce-III atoms order in Cel4Au51 and Ce14Ag51, while the Ce-I order in Cel4Cu51. There is a large linear c ontribution to Cp at T > T-N,T-gamma HT = 0.81 (Au), 1.24 (Ag) and 3.1 (Cu) J/mol K-2, which indicates the coexistence of MO and heavy fermi ons. In the case of Cel4Cu51, the magnetic contribution to Cp from sub lattice Ce-I around T-N,T- resembles that of a modulated system and th e characteristic temperatures for Ce-II and Ce-III atoms are estimated from p(T) as:T-K=16 K and >120 K respectively.