Low-temperature properties of the heavy-fermion compound CeRu2Si2 at the metamagnetic transition

Magnetization measurements performed below 1 K on a single-crystalline sample of the heavy fermion compound CeRu₂Si₂ are reported. The field variation of the linear term of the specific heat derived from these data (via a Maxwell relation) exhibits a large peak at the metamagnetic-like transition at B* (=7.7 atT 0). Thermal-expansion measurements, show a drastic drop of the temperature where a Fermi liquid behavior is reached whenB B*. Similar experiments performed on a single-crystalline Ce_0.95La_0.05Ru₂Si₂ sample show a broadening of all the anomalies atB* and a reduction of their intensities. These results strongly suggest that pure CeRu₂Si₂ approaches a magnetic instability atB* forT 0.