Continuous evolution of fermi surface properties above metamagnetic transitions in Ce_xla_1-xRu₂Si₂

We report the de Haas-van Alphen (dHvA) effect studies above metamagnetic transition fields in Ce_xLa_1-xRu₂Si₂. Three dHvA oscillations β′, γ′, and δ are observed for all the samples from x = 0:0 to 1.0. The frequencies and effective masses of these oscillations vary smoothly with the Ce concentration from LaRu ₂Si₂ to CeRu₂Si₂. The signal magnitude is reduced only by a factor of approximately 1/10 at most even in alloys with a high concentration of Ce. These behaviors are the same as those observed in the alloys of the compounds with localized f electrons, indicating that the f electron maintains localized nature above the metamagnetic transitions.