dHvA effect study of the metamagnetic transition in CeRu2Si2 under pressure

We have performed the de Haas-van Alphen effect study under high pressure f or both the field ranges below and above the metamagnetic transition field (H-m) in CeRu2Si2. The effective masses below H-m decrease considerably wit h pressure as expected from various macroscopic measurements, whereas above H-m it is found that the effective mass for the large hole surface does no t change substantially with pressure. The dHvA oscillations can be traced a ll the way from below to above H-m and it is found that the transition of t he dHvA oscillations takes place in a narrower held range than the transiti on width of magnetization. (C) 1999 Elsevier Science B.V. All rights reserv ed.