Inelastic Neutron Scattering Study of $Ce_3Sn$ and $Ce_3In$

In $Ce_3Sn$ and $Ce_3In$, the linear coefficients of specific heat $\gamma$ are 260 $mJ/mol Ce-K^2$ and 700 $mJ/mol Ce-K^2$, respectively. The Wilson ratio is 7.0 for $Ce_3Sn$ and 11.5 for $Ce_3In$. Such large values suggest the presence of ferromagnetic correlations in the ground state. Hence, this system is a potential candidate for studying the magnetic instability at a quantum critical point (QCP). As an initial measurement, we have measured the magnetic inelastic neutron scattering line shape of polycrystalline samples to determine the crystal field (CF) excitations. The low temperature spectrum of both $Ce_3Sn$ and $Ce_3In$ consist of a quasi- elastic line and two obvious inelastic lines resulting from the two excited crystal field doublets of $Ce^{3+}$ in the tetragonal symmetry. The quasi-elastic linewidth,which is related to the Kondo scale, is 3.2meV for $Ce_3Sn$ and 1.5meV for $Ce_3In$, consistent with the linear coefficients of specific heat. For $Ce_3Sn$ the two CF excitations are at 20meV and 35meV while for $Ce_3In$, the splitting is much larger giving the two excitations at 15meV and 47meV.