Low Temperature Specific Heat of CeRu2Si2 at the Field Induced Metamagnetic Instability

We report specific heat measurements in a broad temperature range between 0.06 and 20 K on single crystalline CeRu₂Si₂ in magnetic fields applied parallel to the c-direction around the critical field B _M , where the metamagnetic transition from the itinerant to the localized state takes place. In the critical field B _M c=7.8 T a distinct deviation from the usual Fermi- liquid behavior is found down to our lowest temperature. Below 1.8 K C/T varies as (1–aT), while for 1.8 K<T<20 K a power law T ^–1 with =0.66 is found. Small deviations from the critical magnetic field leads to the recovery of a Fermi-liquid ground state. The observed behavior of the specific heat at the field induced magnetic instability is discussed in the context of a non-Fermi-liquid state and compared with those for the field-induced nFl CeCu_6–x Ag _x and the recent observation of nFl behavior at B _M in UPt₃.