Absence of a first-order metamagnetic transition in CeRu2Si2

Metamagnetic transition of the heavy-electron compound CeRu2Si2 has been examined on high-purity single crystals by means of a static magnetization measurement at very low temperatures down to 90 mK. No hysteresis is observed in the magnetization process. The peak value of the differential susceptibility at the metamagnetic field BM∼7.7 T follows a simple T2 law below T∼0.5 K, and saturates to a finite value 1.88μB/T Ce as T→0. From these results for two single crystals with slightly different quality, we have confirmed the nonexistence of a first-order phase transition at BM in the clean limit of this system. The itinerant nature of the 4f electrons is most likely preserved in the magnetized state at BBM.