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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.

We have observed a new de Haas-van Alphen (dHvA) oscillation in CeRu 2 Si 2 of frequency 5.36×10 7 Oe and cyclotron effective mass 120 m 0 for magnetic fields along the [100] direction. The new dHvA frequency is thought to arise from the heavy electrons of the large hole surface centered at the Z point which is predicted by the band structure calculations.

We have measured the de Haas-van Alphen effect in the antiferromagnetic compound GdIn 3 . The Fermi surface of GdIn 3 is almost the same as that of the non- f reference compound LaIn 3 . The cyclotron masses of GdIn 3 are also close to those of LaIn 3 . These results indicate that the 4 f electrons in GdIn 3 are well localized and that mass enhancement due to the electron-magnon interaction is extremely small.

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in CeRu 2 Si 2 and LaRu 2 Si 2 . From the results of magnetoresistance, CeRu 2 Si 2 is concluded to be a compensated metal, possibly possessing an open orbit along the c -axis of the tetragonal structure. On the other hand, LaRu 2 Si 2 is an uncompensated metal, showing the saturated magnetoresistance. These results imply that the 4 f electrons in CeRu 2 Si 2 are itinerant. In the dHvA experiments of LaRu 2 Si 2 , we have found a large ellipsoidal Fermi surface which occupies roughly half of the Brillouin zone in volume. On the other hand, CeRu 2 Si 2 possesses multiply connected Fermi surfaces in part, although main Fermi surfaces are not observed yet.

From the de Haas-van Alphen experiments in CeRu 2 Si 2 , an itinerant 4f electron-Fermi surface is most likely changed into the localized one at the metamagnetic transition.

We have determined the scattering lifetime from the field dependence of the dHvA amplitude in the superconducting mixed state of 2H-NbSe2. A so-called Dingle plot shows a straight line, representing no field dependence of the scattering time. The dHvA signal can not be observed in the mixed state of Nb.

We have measured the magnetoresistance and the de Haas-van Alphen effect in CeRu 2 Si 2 to clarify the nature of the 4f electron in CeRu 2 Si 2 .

From de Haas-van Alphen experiments of CeIn 3 and LaIn 3 , we have confirmed that the product of the cyclotron mass and the inverse scattering lifetime is constant.