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We have investigated the Fermi-surface ͑FS͒ properties in the Pr-based filled skutterudite PrOs 4 P 12 and its reference compound LaOs 4 P 12 by means of de Haas-van Alphen experiments and the band-structure calculations. The topology of FS in PrOs 4 P 12 is close to that in the reference compound LaOs 4 P 12 , indicating a localized nature of 4f electrons in PrOs 4 P 12 . Whereas the localized nature of 4f electrons, we have confirmed a highly enhanced cyclotron effective mass of up to 18m 0 in PrOs 4 P 12 , which is enhanced about 3.8 times compared to that in LaOs 4 P 12 . No nesting property with q = ͑1,0,0͒ in the FS of PrOs 4 P 12 has been confirmed in contrast to good nesting properties in PrFe 4 P 12 and PrRu 4 P 12 which exhibit unusual ordered states at low temperatures. A role of both the 4f electron's contributions and the FS nesting property for unusual phase transitions are discussed.

We have succeeded in observing the de Haas-van Alphen effect in PrOs4P12 which shows no anomaly down to 50 mK in contrast to PrFe4P12 and PrRu4P12. The Fermi surface (FS) topology is reasonably explained by the energy band structure calculation based on a full potential linearized augmented-plane-wave method within the local-density-approximation. Whereas the localized nature of 4f -electrons, we have confirmed a highly enhanced cyclotron effective mass up to 18m0 in PrOs4P12, which is enhanced 3.8 times compared to that of LaOs4P12. No nesting property with q = (1, 0, 0) in the FS of PrOs4P12 has been confirmed, which suggests both the 4f -electron's contribution and the FS nesting property play the role for the phase transitions in PrFe4P12 and PrRu4P12.

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We have performed de Haas-van Alphen (dHvA) experiments using micro-cantilever on small single crystal of LaFeGe3 with longest dimension less than 0.1 mm. Detected dHvA frequencies using micro-cantilever shows a good agreement with the result of the band calculation. The micro-cantilever is a hopeful device to detect the dHvA effect for a very small single crystals less than 0.1mm