Ce5Ni6In11: An intermediate heavy-fermion system

Abstract

Low-temperature heat capacity, ac and dc magnetic susceptibility measurements were conducted on the compound ${\mathrm{Ce}}_5$ ${\mathrm{Ni}}_6$ ${\mathrm{In}}_{11}$. The relatively large electronic specific heat coefficient (γ) of 145±20 mJ/mol Ce ${\mathrm{K}}^2$ indicates that ${\mathrm{Ce}}_5$ ${\mathrm{Ni}}_6$ ${\mathrm{In}}_{11}$ 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 states may be much larger (an estimated upper limit of 320 mJ/mol Ce ${\mathrm{K}}^2$) than the value derived from γ=145. The compound undergoes two low-temperature phase transitions at ${\mathit{T}}_{\mathit{N}1}$=0.63 K and ${\mathit{T}}_{\mathit{N}2}$=1.10 K, both being antiferromagnetic in nature. The combined heat capacity, dc and ac susceptibility and structural data suggest that the magnetic structure of ${\mathrm{Ce}}_5$ ${\mathrm{Ni}}_6$ ${\mathrm{In}}_{11}$ is complex, with the two Ce atoms in the 2(c) sublattice of the unit cell ordering at ${\mathit{T}}_{\mathit{N}1}$ and the eight Ce atoms in the 8(p) sublattice ordering at ${\mathit{T}}_{\mathit{N}2}$. There is also some evidence that there is a weak interaction between the two Ce sublattices.