| Summary: | Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas-van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs4AS12 and LaOs4AS12 using magnetic fields of up to 40 T. Several peaks are observed in the low-field susceptibility of PrOs4AS 12, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments show that the Fermi-surface topologies of PrOs4AS12 in its PMM phase and LaOs4AS 12 are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs4AS 12 on the PrOs4AS12 lattice. Both observations suggest that the Pr 4f electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, while the properties of LaOs 4AS12 suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs4AS12. For example, the quasiparticle effective masses in PrOs4AS12 are found to decrease with increasing field, probably reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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