New Features of the Metamagnetic Transition in CeRu2Si2from the dHvA Effect Study under High Pressure

We have studied the Fermi surface properties of CeRu 2 Si 2 below and above the metamagnetic transition (MT) under high pressures. The frequencies of the dHvA oscillations change considerably with pressure both below and above the MT. The pressure coefficient of the frequencies are larger than those of normal metals by more than ten times. The sign and value of the pressure coefficient depend on the dHvA frequency or the orbit. Below the MT the effective masses decrease with increasing pressure, while that above the MT is found to slightly increase. The dHvA oscillations can be traced through the MT at high pressures and it is found that the Fermi surface changes from that of the itinerant f electron to another Fermi surface which is similar to that of the localized f electron in a field range much narrower than that of the MT width in the magnetization. An analysis based on the pressure effect of the Fermi surface indicates that the Fermi surface remains unchanged when the filed approaches the MT field (...