DHVA EFFECT STUDY OF METAMAGNETIC TRANSITION IN CERU2SI2

The de Haas-van Alphen (dHvA) effect measurements have been performed for both the field ranges above and below the metamagnetic transition field (H(m)) in the (010) plane in CeRu2Si2. The experimental frequencies and effective masses below H(m) agree well with the predictions of the first principle or the renormalized band structure calculations based on the itinerant 4f electron model. On the other hand, those above H(m) can be explained well by the localized 4f electron model. The one to one correspondence between the dHvA oscillations below and above H(m) can be made. The frequencies are found to change abruptly around H(m). The effective masses decrease considerably around H(m) and continue to decrease with increasing field. These observations indicate that the 4f electron nature changes from itinerant to localized around H(m).