Investigation of giant crystal electric field (CEF) splitting in CeIr3Si2

CeIr3Si2 exhibits highly anisotropic bulk properties with two magnetic transitions at TN1 ~ 3.9 K and TN2 ~ 3.1 K. The overall CEF splitting of the J=5/2 ground multiplet of this compound is unusually large, 1600 K This large splitting is comparable with that of 2000 K found in the ferromagnet CeRh3B2. Among Ce based compounds, CeIr3Si2 is probably the second compound having a giant CEF splitting. The magnetic entropy of CeIr3Si2 at TN1 ~ 3.9 K is only 0.5Rln2 and recovers the full value of Rln2 at 30K, indicating the presence of short range magnetic correlations above TN1. These features are assumed to be related to very short Ce-Ce distances, 3.6 Å, leading to a large CEF and to a strong hybridization between 4f and 5d or conduction electrons. We therefore propose to carry out inelastic neutron scattering measurements on HET to probe directly the CEF excitations of both multiplets.