A de Haas-van Alphen study of the filled skutterudite compounds PrOs${}_4$As${}_{12}$ and LaOs${}_4$As${}_{12}$

Abstract

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 PrOs${}_4$As${}_{12}$ and LaOs${}_4$As${}_{12}$ using magnetic fields of up to 40~T. Several peaks are observed in the low-field susceptibility of PrOs${}_4$As${}_{12}$, 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 PrOs${}_4$As${}_{12}$ in its PMM phase and LaOs${}_4$As${}_{12}$ are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs${}_4$As${}_{12}$ on the PrOs${}_4$As${}_{12}$ lattice. Both observations suggest that the Pr 4$f$ electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, whilst the properties of LaOs${}_4$As${}_{12}$ suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs${}_4$As${}_{12}$. For example, the quasiparticle effective masses in PrOs${}_4$As${}_{12}$ 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.