Transition offelectron nature from itinerant to localized: Metamagnetic transition inCeRu2Si2studied via the de Haas–van Alphen effect

We report the measurements of the de Haas--van Alphen (dHvA) effect for field ranges below and above the metamagnetic transition field (${\mathit{H}}_{\mathit{m}}$) in ${\mathrm{CeRu}}_{2}$${\mathrm{Si}}_{2}$. The dHvA frequency branches and the effective masses ranging from 1.5${\mathit{m}}_{0}$ to 120${\mathit{m}}_{0}$ observed below ${\mathit{H}}_{\mathit{m}}$ agree with the predictions of the itinerant f electron model, whereas those above ${\mathit{H}}_{\mathit{m}}$ can be explained well with the localized f electron model. All the dHvA frequencies change abruptly around ${\mathit{H}}_{\mathit{m}}$. The effective masses decrease considerably around ${\mathit{H}}_{\mathit{m}}$ and then continue to decrease with increasing field.