CE5NI6IN11 - AN INTERMEDIATE HEAVY-FERMION SYSTEM

Low-temperature heat capacity, ac and de magnetic susceptibility measu rements were conducted on the compound Ce5Ni6In11. The relatively larg e electronic specific heat coefficient (gamma) of 145+/-20 mJ/mol Ce K -2 indicates that Ce5Ni6In11 is an intermediate heavy fermion. Because of the complex structure of this phase, the true density of states of the Ce atoms which contribute to the highly correlated electron state s may be much larger (an estimated upper limit of 320 mJ/mol Ce K-2) t han the value derived from gamma=145. The compound undergoes two low-t emperature phase transitions at T-N1=0.63 K and T-N2=1.10 K, both bein g antiferromagnetic in nature. The combined heat capacity, de and ac s usceptibility and structural data suggest that the magnetic structure of Ce5Ni6In11 is complex, with the two Ce atoms in the 2(c) sublattice of the unit cell ordering at T-N1 and the eight Ce atoms in the 8(p) sublattice ordering at T-N2. There is also some evidence that there is a weak interaction between the two Ce sublattices.